diff --git a/NOTICE.txt b/NOTICE.txt
index a5369e791..97b38fd63 100644
--- a/NOTICE.txt
+++ b/NOTICE.txt
@@ -3,3 +3,7 @@ Copyright 2001-2024 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (https://www.apache.org/).
+
+The Java source file src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
+is from https://github.com/hazelcast/hazelcast and the following notice applies:
+Copyright (c) 2008-2020, Hazelcast, Inc. All Rights Reserved.
diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index cb39c1d33..b30019ee5 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -44,6 +44,7 @@
     <action type="add" dev="ggregory" due-to="Gary Gregory">Add TreeBag.TreeBag(Iterable).</action>
     <action type="add" issue="COLLECTIONS-858" dev="ggregory" due-to="Alexey Pelykh, Alex Herbert, Gary Gregory">Add CartesianProductIterator #509.</action>
     <action type="add" dev="ggregory" due-to="Gary Gregory">Add missing methods in AbstractMapTests.</action>
+    <action type="add" dev="ggregory" due-to="Gary Gregory">Add ConcurrentReferenceHashMap.</action>
     <!-- UPDATE -->
     <action type="update" issue="COLLECTIONS-857" dev="ggregory" due-to="Claude Warren">Update bloom filter documentation #508.</action>
     <action type="update" dev="ggregory" due-to="Dependabot, Gary Gregory">Bump commons-codec:commons-codec from 1.17.0 to 1.17.1 #514.</action>
diff --git a/src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java b/src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
new file mode 100644
index 000000000..74739d7b8
--- /dev/null
+++ b/src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
@@ -0,0 +1,1885 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * Copyright (c) 2008-2020, Hazelcast, Inc. All Rights Reserved.
+ */
+
+package org.apache.commons.collections4.map;
+
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
+import java.lang.ref.WeakReference;
+import java.util.AbstractCollection;
+import java.util.AbstractMap;
+import java.util.AbstractSet;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.ConcurrentModificationException;
+import java.util.EnumSet;
+import java.util.Enumeration;
+import java.util.HashMap;
+import java.util.Hashtable;
+import java.util.IdentityHashMap;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.util.Set;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+/**
+ * An advanced hash map supporting configurable garbage collection semantics of keys and values, optional referential-equality, full concurrency of retrievals,
+ * and adjustable expected concurrency for updates.
+ * <p>
+ * This map is designed around specific advanced use-cases. If there is any doubt whether this map is for you, you most likely should be using
+ * {@link java.util.concurrent.ConcurrentHashMap} instead.
+ * </p>
+ * <p>
+ * This map supports strong, weak, and soft keys and values. By default, keys are weak, and values are strong. Such a configuration offers similar behavior to
+ * {@link java.util.WeakHashMap}, entries of this map are periodically removed once their corresponding keys are no longer referenced outside of this map. In
+ * other words, this map will not prevent a key from being discarded by the garbage collector. Once a key has been discarded by the collector, the corresponding
+ * entry is no longer visible to this map; however, the entry may occupy space until a future map operation decides to reclaim it. For this reason, summary
+ * functions such as {@code size} and {@code isEmpty} might return a value greater than the observed number of entries. In order to support a high level of
+ * concurrency, stale entries are only reclaimed during blocking (usually mutating) operations.
+ * </p>
+ * <p>
+ * Enabling soft keys allows entries in this map to remain until their space is absolutely needed by the garbage collector. This is unlike weak keys which can
+ * be reclaimed as soon as they are no longer referenced by a normal strong reference. The primary use case for soft keys is a cache, which ideally occupies
+ * memory that is not in use for as long as possible.
+ * </p>
+ * <p>
+ * By default, values are held using a normal strong reference. This provides the commonly desired guarantee that a value will always have at least the same
+ * life-span as its key. For this reason, care should be taken to ensure that a value never refers, either directly or indirectly, to its key, thereby
+ * preventing reclamation. If this is unavoidable, then it is recommended to use the same reference type in use for the key. However, it should be noted that
+ * non-strong values may disappear before their corresponding key.
+ * </p>
+ * <p>
+ * While this map does allow the use of both strong keys and values, it is recommended you use {@link java.util.concurrent.ConcurrentHashMap} for such a
+ * configuration, since it is optimized for that case.
+ * </p>
+ * <p>
+ * Just like {@link java.util.concurrent.ConcurrentHashMap}, this class obeys the same functional specification as {@link Hashtable}, and includes versions of
+ * methods corresponding to each method of {@code Hashtable}. However, even though all operations are thread-safe, retrieval operations do <em>not</em> entail
+ * locking, and there is <em>not</em> any support for locking the entire map in a way that prevents all access. This class is fully interoperable with
+ * {@code Hashtable} in programs that rely on its thread safety but not on its synchronization details.
+ * </p>
+ * <p>
+ * Retrieval operations (including {@code get}) generally do not block, so they may overlap with update operations (including {@code put} and {@code remove}).
+ * Retrievals reflect the results of the most recently <em>completed</em> update operations holding upon their onset. For aggregate operations such as
+ * {@code putAll} and {@code clear}, concurrent retrievals may reflect insertion or removal of only some entries. Similarly, Iterators and Enumerations return
+ * elements reflecting the state of the hash map at some point at or since the creation of the iterator/enumeration. They do <em>not</em> throw
+ * {@link ConcurrentModificationException}. However, iterators are designed to be used by only one thread at a time.
+ * </p>
+ * <p>
+ * The allowed concurrency among update operations is guided by the optional {@code concurrencyLevel} constructor argument (default
+ * {@value #DEFAULT_CONCURRENCY_LEVEL}), which is used as a hint for internal sizing. The map is internally partitioned to try to permit the indicated number of
+ * concurrent updates without contention. Because placement in hash tables is essentially random, the actual concurrency will vary. Ideally, you should choose a
+ * value to accommodate as many threads as will ever concurrently modify the map. Using a significantly higher value than you need can waste space and time, and
+ * a significantly lower value can lead to thread contention. But overestimates and underestimates within an order of magnitude do not usually have much
+ * noticeable impact. A value of one is appropriate when it is known that only one thread will modify and all others will only read. Also, resizing this or any
+ * other kind of hash map is a relatively slow operation, so, when possible, it is a good idea that you provide estimates of expected map sizes in constructors.
+ * </p>
+ * <p>
+ * This class and its views and iterators implement all of the <em>optional</em> methods of the {@link Map} and {@link Iterator} interfaces.
+ * </p>
+ * <p>
+ * Like {@link Hashtable} but unlike {@link HashMap}, this class does <em>not</em> allow {@code null} to be used as a key or value.
+ * </p>
+ * <p>
+ * Provenance: Copied and edited from Apache Groovy git master at commit 77dc80a7512ceb2168b1bc866c3d0c69b002fe11; via Doug Lea, Jason T. Greene, with
+ * assistance from members of JCP JSR-166, and Hazelcast.
+ * </p>
+ *
+ * @param <K> the type of keys maintained by this map.
+ * @param <V> the type of mapped values.
+ */
+public class ConcurrentReferenceHashMap<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V> {
+
+    /**
+     * Builds new ConcurrentReferenceHashMap instances.
+     * <p>
+     * By default, keys are weak, and values are strong.
+     * </p>
+     * <p>
+     * The default values are:
+     * </p>
+     * <ul>
+     * <li>concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}</li>
+     * <li>initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}</li>
+     * <li>key reference type: {@link ReferenceType#WEAK}</li>
+     * <li>load factor: {@value #DEFAULT_LOAD_FACTOR}</li>
+     * <li>options: {@code null}</li>
+     * <li>source map: {@code null}</li>
+     * <li>value reference type: {@link ReferenceType#STRONG}</li>
+     * </ul>
+     *
+     * @param <K> the type of keys.
+     * @param <V> the type of values.
+     */
+    public static class Builder<K, V> implements Supplier<ConcurrentReferenceHashMap<K, V>> {
+
+        private static final Map<?, ?> DEFAULT_SOURCE_MAP = null;
+
+        private int initialCapacity = DEFAULT_INITIAL_CAPACITY;
+        private float loadFactor = DEFAULT_LOAD_FACTOR;
+        private int concurrencyLevel = DEFAULT_CONCURRENCY_LEVEL;
+        private ReferenceType keyReferenceType = DEFAULT_KEY_TYPE;
+        private ReferenceType valueReferenceType = DEFAULT_VALUE_TYPE;
+        private EnumSet<Option> options = DEFAULT_OPTIONS;
+        @SuppressWarnings("unchecked")
+        private Map<? extends K, ? extends V> sourceMap = (Map<? extends K, ? extends V>) DEFAULT_SOURCE_MAP;
+
+        /**
+         * Builds a new {@link ConcurrentReferenceHashMap}.
+         * <p>
+         * By default, keys are weak, and values are strong.
+         * </p>
+         * <p>
+         * The default values are:
+         * </p>
+         * <ul>
+         * <li>concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}</li>
+         * <li>initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}</li>
+         * <li>key reference type: {@link ReferenceType#WEAK}</li>
+         * <li>load factor: {@value #DEFAULT_LOAD_FACTOR}</li>
+         * <li>options: {@code null}</li>
+         * <li>source map: {@code null}</li>
+         * <li>value reference type: {@link ReferenceType#STRONG}</li>
+         * </ul>
+         */
+        @Override
+        public ConcurrentReferenceHashMap<K, V> get() {
+            final ConcurrentReferenceHashMap<K, V> map = new ConcurrentReferenceHashMap<>(initialCapacity, loadFactor, concurrencyLevel, keyReferenceType,
+                    valueReferenceType, options);
+            if (sourceMap != null) {
+                map.putAll(sourceMap);
+            }
+            return map;
+        }
+
+        /**
+         * Sets the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.
+         *
+         * @param concurrencyLevel estimated number of concurrently updating threads
+         * @return this instance.
+         */
+        public Builder<K, V> setConcurrencyLevel(final int concurrencyLevel) {
+            this.concurrencyLevel = concurrencyLevel;
+            return this;
+        }
+
+        /**
+         * Sets the initial capacity. The implementation performs internal sizing to accommodate this many elements.
+         *
+         * @param initialCapacity the initial capacity.
+         * @return this instance.
+         */
+        public Builder<K, V> setInitialCapacity(final int initialCapacity) {
+            this.initialCapacity = initialCapacity;
+            return this;
+        }
+
+        /**
+         * Sets the reference type to use for keys.
+         *
+         * @param keyReferenceType the reference type to use for keys.
+         * @return this instance.
+         */
+        public Builder<K, V> setKeyReferenceType(final ReferenceType keyReferenceType) {
+            this.keyReferenceType = keyReferenceType;
+            return this;
+        }
+
+        /**
+         * Sets the load factor factor, used to control resizing. Resizing may be performed when the average number of elements per bin exceeds this threshold.
+         *
+         * @param loadFactor the load factor factor, used to control resizing
+         * @return this instance.
+         */
+        public Builder<K, V> setLoadFactor(final float loadFactor) {
+            this.loadFactor = loadFactor;
+            return this;
+        }
+
+        /**
+         * Sets the behavioral options.
+         *
+         * @param options the behavioral options.
+         * @return this instance.
+         */
+        public Builder<K, V> setOptions(final EnumSet<Option> options) {
+            this.options = options;
+            return this;
+        }
+
+        /**
+         * Sets the values to load into a new map.
+         *
+         * @param sourceMap the values to load into a new map.
+         * @return this instance.
+         */
+        public Builder<K, V> setSourceMap(final Map<? extends K, ? extends V> sourceMap) {
+            this.sourceMap = sourceMap;
+            return this;
+        }
+
+        /**
+         * Sets the reference type to use for values.
+         *
+         * @param valueReferenceType the reference type to use for values.
+         * @return this instance.
+         */
+        public Builder<K, V> setValueReferenceType(final ReferenceType valueReferenceType) {
+            this.valueReferenceType = valueReferenceType;
+            return this;
+        }
+
+        /**
+         * Sets key reference type to {@link ReferenceType#SOFT}.
+         *
+         * @return this instance.
+         */
+        public Builder<K, V> softKeys() {
+            setKeyReferenceType(ReferenceType.SOFT);
+            return this;
+        }
+
+        /**
+         * Sets value reference type to {@link ReferenceType#SOFT}.
+         *
+         * @return this instance.
+         */
+        public Builder<K, V> softValues() {
+            setValueReferenceType(ReferenceType.SOFT);
+            return this;
+        }
+
+        /**
+         * Sets key reference type to {@link ReferenceType#STRONG}.
+         *
+         * @return this instance.
+         */
+        public Builder<K, V> strongKeys() {
+            setKeyReferenceType(ReferenceType.STRONG);
+            return this;
+        }
+
+        /**
+         * Sets value reference type to {@link ReferenceType#STRONG}.
+         *
+         * @return this instance.
+         */
+        public Builder<K, V> strongValues() {
+            setValueReferenceType(ReferenceType.STRONG);
+            return this;
+        }
+
+        /**
+         * Sets key reference type to {@link ReferenceType#WEAK}.
+         *
+         * @return this instance.
+         */
+        public Builder<K, V> weakKeys() {
+            setKeyReferenceType(ReferenceType.WEAK);
+            return this;
+        }
+
+        /**
+         * Sets value reference type to {@link ReferenceType#WEAK}.
+         *
+         * @return this instance.
+         */
+        public Builder<K, V> weakValues() {
+            setValueReferenceType(ReferenceType.WEAK);
+            return this;
+        }
+
+    }
+
+    /**
+     * The basic strategy is to subdivide the table among Segments, each of which itself is a concurrently readable hash table.
+     */
+    private final class CachedEntryIterator extends HashIterator implements Iterator<Entry<K, V>> {
+        private final InitializableEntry<K, V> entry = new InitializableEntry<>();
+
+        @Override
+        public Entry<K, V> next() {
+            final HashEntry<K, V> e = super.nextEntry();
+            return entry.init(e.key(), e.value());
+        }
+    }
+
+    private final class EntryIterator extends HashIterator implements Iterator<Entry<K, V>> {
+        @Override
+        public Entry<K, V> next() {
+            final HashEntry<K, V> e = super.nextEntry();
+            return new WriteThroughEntry(e.key(), e.value());
+        }
+    }
+
+    private final class EntrySet extends AbstractSet<Entry<K, V>> {
+
+        private final boolean cached;
+
+        private EntrySet(final boolean cached) {
+            this.cached = cached;
+        }
+
+        @Override
+        public void clear() {
+            ConcurrentReferenceHashMap.this.clear();
+        }
+
+        @Override
+        public boolean contains(final Object o) {
+            if (!(o instanceof Map.Entry)) {
+                return false;
+            }
+            final Entry<?, ?> e = (Entry<?, ?>) o;
+            final V v = ConcurrentReferenceHashMap.this.get(e.getKey());
+            return v != null && v.equals(e.getValue());
+        }
+
+        @Override
+        public boolean isEmpty() {
+            return ConcurrentReferenceHashMap.this.isEmpty();
+        }
+
+        @Override
+        public Iterator<Entry<K, V>> iterator() {
+            return cached ? new CachedEntryIterator() : new EntryIterator();
+        }
+
+        @Override
+        public boolean remove(final Object o) {
+            if (!(o instanceof Map.Entry)) {
+                return false;
+            }
+            final Entry<?, ?> e = (Entry<?, ?>) o;
+            return ConcurrentReferenceHashMap.this.remove(e.getKey(), e.getValue());
+        }
+
+        @Override
+        public int size() {
+            return ConcurrentReferenceHashMap.this.size();
+        }
+    }
+
+    /**
+     * ConcurrentReferenceHashMap list entry. Note that this is never exported out as a user-visible Map.Entry.
+     * <p>
+     * Because the value field is volatile, not final, it is legal wrt the Java Memory Model for an unsynchronized reader to see null instead of initial value
+     * when read via a data race. Although a reordering leading to this is not likely to ever actually occur, the Segment.readValueUnderLock method is used as a
+     * backup in case a null (pre-initialized) value is ever seen in an unsynchronized access method.
+     * </p>
+     */
+    private static final class HashEntry<K, V> {
+
+        @SuppressWarnings("unchecked")
+        static <K, V> HashEntry<K, V>[] newArray(final int i) {
+            return new HashEntry[i];
+        }
+
+        private final Object keyRef;
+        private final int hash;
+        private volatile Object valueRef;
+        private final HashEntry<K, V> next;
+
+        HashEntry(final K key, final int hash, final HashEntry<K, V> next, final V value, final ReferenceType keyType, final ReferenceType valueType,
+                final ReferenceQueue<Object> refQueue) {
+            this.hash = hash;
+            this.next = next;
+            this.keyRef = newKeyReference(key, keyType, refQueue);
+            this.valueRef = newValueReference(value, valueType, refQueue);
+        }
+
+        @SuppressWarnings("unchecked")
+        V dereferenceValue(final Object value) {
+            if (value instanceof KeyReference) {
+                return ((Reference<V>) value).get();
+            }
+            return (V) value;
+        }
+
+        @SuppressWarnings("unchecked")
+        K key() {
+            if (keyRef instanceof KeyReference) {
+                return ((Reference<K>) keyRef).get();
+            }
+            return (K) keyRef;
+        }
+
+        Object newKeyReference(final K key, final ReferenceType keyType, final ReferenceQueue<Object> refQueue) {
+            if (keyType == ReferenceType.WEAK) {
+                return new WeakKeyReference<>(key, hash, refQueue);
+            }
+            if (keyType == ReferenceType.SOFT) {
+                return new SoftKeyReference<>(key, hash, refQueue);
+            }
+
+            return key;
+        }
+
+        Object newValueReference(final V value, final ReferenceType valueType, final ReferenceQueue<Object> refQueue) {
+            if (valueType == ReferenceType.WEAK) {
+                return new WeakValueReference<>(value, keyRef, hash, refQueue);
+            }
+            if (valueType == ReferenceType.SOFT) {
+                return new SoftValueReference<>(value, keyRef, hash, refQueue);
+            }
+
+            return value;
+        }
+
+        void setValue(final V value, final ReferenceType valueType, final ReferenceQueue<Object> refQueue) {
+            this.valueRef = newValueReference(value, valueType, refQueue);
+        }
+
+        V value() {
+            return dereferenceValue(valueRef);
+        }
+    }
+
+    private abstract class HashIterator {
+        private int nextSegmentIndex;
+        private int nextTableIndex;
+        private HashEntry<K, V>[] currentTable;
+        private HashEntry<K, V> nextEntry;
+        private HashEntry<K, V> lastReturned;
+        // Strong reference to weak key (prevents gc)
+        private K currentKey;
+
+        private HashIterator() {
+            nextSegmentIndex = segments.length - 1;
+            nextTableIndex = -1;
+            advance();
+        }
+
+        final void advance() {
+            if (nextEntry != null && (nextEntry = nextEntry.next) != null) {
+                return;
+            }
+            while (nextTableIndex >= 0) {
+                if ((nextEntry = currentTable[nextTableIndex--]) != null) {
+                    return;
+                }
+            }
+            while (nextSegmentIndex >= 0) {
+                final Segment<K, V> seg = segments[nextSegmentIndex--];
+                if (seg.count != 0) {
+                    currentTable = seg.table;
+                    for (int j = currentTable.length - 1; j >= 0; --j) {
+                        if ((nextEntry = currentTable[j]) != null) {
+                            nextTableIndex = j - 1;
+                            return;
+                        }
+                    }
+                }
+            }
+        }
+
+        public boolean hasMoreElements() {
+            return hasNext();
+        }
+
+        public boolean hasNext() {
+            while (nextEntry != null) {
+                if (nextEntry.key() != null) {
+                    return true;
+                }
+                advance();
+            }
+            return false;
+        }
+
+        HashEntry<K, V> nextEntry() {
+            do {
+                if (nextEntry == null) {
+                    throw new NoSuchElementException();
+                }
+                lastReturned = nextEntry;
+                currentKey = lastReturned.key();
+                advance();
+            } while /* Skip GC'd keys */ (currentKey == null);
+            return lastReturned;
+        }
+
+        public void remove() {
+            if (lastReturned == null) {
+                throw new IllegalStateException();
+            }
+            ConcurrentReferenceHashMap.this.remove(currentKey);
+            lastReturned = null;
+        }
+    }
+
+    private static final class InitializableEntry<K, V> implements Entry<K, V> {
+        private K key;
+        private V value;
+
+        @Override
+        public K getKey() {
+            return key;
+        }
+
+        @Override
+        public V getValue() {
+            return value;
+        }
+
+        public Entry<K, V> init(final K key, final V value) {
+            this.key = key;
+            this.value = value;
+            return this;
+        }
+
+        @Override
+        public V setValue(final V value) {
+            throw new UnsupportedOperationException();
+        }
+    }
+
+    private final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
+        @Override
+        public K next() {
+            return super.nextEntry().key();
+        }
+
+        @Override
+        public K nextElement() {
+            return super.nextEntry().key();
+        }
+    }
+
+    private interface KeyReference {
+        int keyHash();
+
+        Object keyRef();
+    }
+
+    private final class KeySet extends AbstractSet<K> {
+        @Override
+        public void clear() {
+            ConcurrentReferenceHashMap.this.clear();
+        }
+
+        @Override
+        public boolean contains(final Object o) {
+            return ConcurrentReferenceHashMap.this.containsKey(o);
+        }
+
+        @Override
+        public boolean isEmpty() {
+            return ConcurrentReferenceHashMap.this.isEmpty();
+        }
+
+        @Override
+        public Iterator<K> iterator() {
+            return new KeyIterator();
+        }
+
+        @Override
+        public boolean remove(final Object o) {
+            return ConcurrentReferenceHashMap.this.remove(o) != null;
+        }
+
+        @Override
+        public int size() {
+            return ConcurrentReferenceHashMap.this.size();
+        }
+    }
+
+    /**
+     * Behavior-changing configuration options for the map
+     */
+    public enum Option {
+        /**
+         * Indicates that referential-equality (== instead of .equals()) should be used when locating keys. This offers similar behavior to
+         * {@link IdentityHashMap}
+         */
+        IDENTITY_COMPARISONS
+    }
+
+    /**
+     * An option specifying which Java reference type should be used to refer to a key and/or value.
+     */
+    public enum ReferenceType {
+        /**
+         * Indicates a normal Java strong reference should be used
+         */
+        STRONG,
+        /**
+         * Indicates a {@link WeakReference} should be used
+         */
+        WEAK,
+        /**
+         * Indicates a {@link SoftReference} should be used
+         */
+        SOFT
+    }
+
+    /**
+     * Segments are specialized versions of hash tables. This subclasses from ReentrantLock opportunistically, just to simplify some locking and avoid separate
+     * construction.
+     * <p>
+     * Segments maintain a table of entry lists that are ALWAYS kept in a consistent state, so they can be read without locking. Next fields of nodes are
+     * immutable (final). All list additions are performed at the front of each bin. This makes it easy to check changes, and also fast to traverse. When nodes
+     * would otherwise be changed, new nodes are created to replace them. This works well for hash tables since the bin lists tend to be short. (The average
+     * length is less than two for the default load factor threshold.)
+     * </p>
+     * <p>
+     * Read operations can thus proceed without locking, but rely on selected uses of volatiles to ensure that completed write operations performed by other
+     * threads are noticed. For most purposes, the "count" field, tracking the number of elements, serves as that volatile variable ensuring visibility. This is
+     * convenient because this field needs to be read in many read operations anyway:
+     * </p>
+     * <ul>
+     * <li>All (unsynchronized) read operations must first read the "count" field, and should not look at table entries if it is 0.</li>
+     * <li>All (synchronized) write operations should write to the "count" field after structurally changing any bin. The operations must not take any action
+     * that could even momentarily cause a concurrent read operation to see inconsistent data. This is made easier by the nature of the read operations in Map.
+     * For example, no operation can reveal that the table has grown but the threshold has not yet been updated, so there are no atomicity requirements for this
+     * with respect to reads.</li>
+     * </ul>
+     * <p>
+     * As a guide, all critical volatile reads and writes to the count field are marked in code comments.
+     * </p>
+     */
+    private static final class Segment<K, V> extends ReentrantLock {
+
+        private static final long serialVersionUID = 1L;
+
+        @SuppressWarnings("unchecked")
+        static <K, V> Segment<K, V>[] newArray(final int i) {
+            return new Segment[i];
+        }
+
+        /**
+         * The number of elements in this segment's region.
+         */
+        // @SuppressFBWarnings(value = "SE_TRANSIENT_FIELD_NOT_RESTORED", justification =
+        // "I trust Doug Lea's technical decision")
+        private transient volatile int count;
+
+        /**
+         * Number of updates that alter the size of the table. This is used during bulk-read methods to make sure they see a consistent snapshot: If modCounts
+         * change during a traversal of segments computing size or checking containsValue, then we might have an inconsistent view of state so (usually) we must
+         * retry.
+         */
+        // @SuppressFBWarnings(value = "SE_TRANSIENT_FIELD_NOT_RESTORED", justification =
+        // "I trust Doug Lea's technical decision")
+        private transient int modCount;
+
+        /**
+         * The table is rehashed when its size exceeds this threshold. (The value of this field is always <tt>(int)(capacity *
+         * loadFactor)</tt>.)
+         */
+        private transient int threshold;
+
+        /**
+         * The per-segment table.
+         */
+        private transient volatile HashEntry<K, V>[] table;
+
+        /**
+         * The load factor for the hash table. Even though this value is same for all segments, it is replicated to avoid needing links to outer object.
+         */
+        private final float loadFactor;
+
+        /**
+         * The collected weak-key reference queue for this segment. This should be (re)initialized whenever table is assigned,
+         */
+        private transient volatile ReferenceQueue<Object> refQueue;
+
+        private final ReferenceType keyType;
+
+        private final ReferenceType valueType;
+
+        private final boolean identityComparisons;
+
+        Segment(final int initialCapacity, final float loadFactor, final ReferenceType keyType, final ReferenceType valueType,
+                final boolean identityComparisons) {
+            this.loadFactor = loadFactor;
+            this.keyType = keyType;
+            this.valueType = valueType;
+            this.identityComparisons = identityComparisons;
+            setTable(HashEntry.<K, V>newArray(initialCapacity));
+        }
+
+        V apply(final K key, final int hash, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+            lock();
+            try {
+                final V oldValue = get(key, hash);
+                final V newValue = remappingFunction.apply(key, oldValue);
+
+                if (newValue == null) {
+                    // delete mapping
+                    if (oldValue != null) {
+                        // something to remove
+                        removeInternal(key, hash, oldValue, false);
+                    }
+                    return null;
+                }
+                // add or replace old mapping
+                putInternal(key, hash, newValue, null, false);
+                return newValue;
+            } finally {
+                unlock();
+            }
+        }
+
+        V applyIfPresent(final K key, final int hash, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+            lock();
+            try {
+                final V oldValue = get(key, hash);
+                if (oldValue == null) {
+                    return null;
+                }
+
+                final V newValue = remappingFunction.apply(key, oldValue);
+
+                if (newValue == null) {
+                    removeInternal(key, hash, oldValue, false);
+                    return null;
+                }
+                putInternal(key, hash, newValue, null, false);
+                return newValue;
+            } finally {
+                unlock();
+            }
+        }
+
+        void clear() {
+            if (count != 0) {
+                lock();
+                try {
+                    final HashEntry<K, V>[] tab = table;
+                    Arrays.fill(tab, null);
+                    ++modCount;
+                    // replace the reference queue to avoid unnecessary stale cleanups
+                    refQueue = new ReferenceQueue<>();
+                    // write-volatile
+                    count = 0;
+                } finally {
+                    unlock();
+                }
+            }
+        }
+
+        boolean containsKey(final Object key, final int hash) {
+            // read-volatile
+            if (count != 0) {
+                HashEntry<K, V> e = getFirst(hash);
+                while (e != null) {
+                    if (e.hash == hash && keyEq(key, e.key())) {
+                        return true;
+                    }
+                    e = e.next;
+                }
+            }
+            return false;
+        }
+
+        boolean containsValue(final Object value) {
+            // read-volatile
+            if (count != 0) {
+                final HashEntry<K, V>[] tab = table;
+                final int len = tab.length;
+                for (int i = 0; i < len; i++) {
+                    for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
+                        final Object opaque = e.valueRef;
+                        V v;
+                        if (opaque == null) {
+                            // recheck
+                            v = readValueUnderLock(e);
+                        } else {
+                            v = e.dereferenceValue(opaque);
+                        }
+                        if (value.equals(v)) {
+                            return true;
+                        }
+                    }
+                }
+            }
+            return false;
+        }
+
+        /* Specialized implementations of map methods */
+        V get(final Object key, final int hash) {
+            // read-volatile
+            if (count != 0) {
+                HashEntry<K, V> e = getFirst(hash);
+                while (e != null) {
+                    if (e.hash == hash && keyEq(key, e.key())) {
+                        final Object opaque = e.valueRef;
+                        if (opaque != null) {
+                            return e.dereferenceValue(opaque);
+                        }
+                        // recheck
+                        return readValueUnderLock(e);
+                    }
+                    e = e.next;
+                }
+            }
+            return null;
+        }
+
+        /**
+         * Gets properly casted first entry of bin for given hash.
+         */
+        HashEntry<K, V> getFirst(final int hash) {
+            final HashEntry<K, V>[] tab = table;
+            return tab[hash & tab.length - 1];
+        }
+
+        V getValue(final K key, final V value, final Function<? super K, ? extends V> function) {
+            return value != null ? value : function.apply(key);
+        }
+
+        private boolean keyEq(final Object src, final Object dest) {
+            return identityComparisons ? src == dest : src.equals(dest);
+        }
+
+        HashEntry<K, V> newHashEntry(final K key, final int hash, final HashEntry<K, V> next, final V value) {
+            return new HashEntry<>(key, hash, next, value, keyType, valueType, refQueue);
+        }
+
+        /**
+         * This method must be called with exactly one of <code>value</code> and <code>function</code> non-null.
+         **/
+        V put(final K key, final int hash, final V value, final Function<? super K, ? extends V> function, final boolean onlyIfAbsent) {
+            lock();
+            try {
+                return putInternal(key, hash, value, function, onlyIfAbsent);
+            } finally {
+                unlock();
+            }
+        }
+
+        private V putInternal(final K key, final int hash, final V value, final Function<? super K, ? extends V> function, final boolean onlyIfAbsent) {
+            removeStale();
+            int c = count;
+            // ensure capacity
+            if (c++ > threshold) {
+                final int reduced = rehash();
+                // adjust from possible weak cleanups
+                if (reduced > 0) {
+                    // write-volatile
+                    count = (c -= reduced) - 1;
+                }
+            }
+            final HashEntry<K, V>[] tab = table;
+            final int index = hash & tab.length - 1;
+            final HashEntry<K, V> first = tab[index];
+            HashEntry<K, V> e = first;
+            while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
+                e = e.next;
+            }
+            V resultValue;
+            if (e != null) {
+                resultValue = e.value();
+                if (!onlyIfAbsent) {
+                    e.setValue(getValue(key, value, function), valueType, refQueue);
+                }
+            } else {
+                final V v = getValue(key, value, function);
+                resultValue = function != null ? v : null;
+
+                if (v != null) {
+                    ++modCount;
+                    tab[index] = newHashEntry(key, hash, first, v);
+                    // write-volatile
+                    count = c;
+                }
+            }
+            return resultValue;
+        }
+
+        /**
+         * Reads value field of an entry under lock. Called if value field ever appears to be null. This is possible only if a compiler happens to reorder a
+         * HashEntry initialization with its table assignment, which is legal under memory model but is not known to ever occur.
+         */
+        V readValueUnderLock(final HashEntry<K, V> e) {
+            lock();
+            try {
+                removeStale();
+                return e.value();
+            } finally {
+                unlock();
+            }
+        }
+
+        int rehash() {
+            final HashEntry<K, V>[] oldTable = table;
+            final int oldCapacity = oldTable.length;
+            if (oldCapacity >= MAXIMUM_CAPACITY) {
+                return 0;
+            }
+            //
+            // Reclassify nodes in each list to new Map. Because we are using power-of-two expansion, the elements from each bin must either stay at the same
+            // index, or move with a power of two offset. We eliminate unnecessary node creation by catching cases where old nodes can be reused because their
+            // next fields won't change. Statistically, at the default threshold, only about one-sixth of them need cloning when a table doubles. The nodes they
+            // replace will be garbage collectable as soon as they are no longer referenced by any reader thread that may be in the midst of traversing table
+            // right now.
+            //
+            final HashEntry<K, V>[] newTable = HashEntry.newArray(oldCapacity << 1);
+            threshold = (int) (newTable.length * loadFactor);
+            final int sizeMask = newTable.length - 1;
+            int reduce = 0;
+            for (int i = 0; i < oldCapacity; i++) {
+                // We need to guarantee that any existing reads of old Map can
+                // proceed. So we cannot yet null out each bin.
+                final HashEntry<K, V> e = oldTable[i];
+                if (e != null) {
+                    final HashEntry<K, V> next = e.next;
+                    final int idx = e.hash & sizeMask;
+                    // Single node on list
+                    if (next == null) {
+                        newTable[idx] = e;
+                    } else {
+                        // Reuse trailing consecutive sequence at same slot
+                        HashEntry<K, V> lastRun = e;
+                        int lastIdx = idx;
+                        for (HashEntry<K, V> last = next; last != null; last = last.next) {
+                            final int k = last.hash & sizeMask;
+                            if (k != lastIdx) {
+                                lastIdx = k;
+                                lastRun = last;
+                            }
+                        }
+                        newTable[lastIdx] = lastRun;
+                        // Clone all remaining nodes
+                        for (HashEntry<K, V> p = e; p != lastRun; p = p.next) {
+                            // Skip GC'd weak refs
+                            final K key = p.key();
+                            if (key == null) {
+                                reduce++;
+                                continue;
+                            }
+                            final int k = p.hash & sizeMask;
+                            final HashEntry<K, V> n = newTable[k];
+                            newTable[k] = newHashEntry(key, p.hash, n, p.value());
+                        }
+                    }
+                }
+            }
+            table = newTable;
+            return reduce;
+        }
+
+        /**
+         * Removes match on key only if value is null, else match both.
+         */
+        V remove(final Object key, final int hash, final Object value, final boolean refRemove) {
+            lock();
+            try {
+                return removeInternal(key, hash, value, refRemove);
+            } finally {
+                unlock();
+            }
+        }
+
+        private V removeInternal(final Object key, final int hash, final Object value, final boolean refRemove) {
+            if (!refRemove) {
+                removeStale();
+            }
+            int c = count - 1;
+            final HashEntry<K, V>[] tab = table;
+            final int index = hash & tab.length - 1;
+            final HashEntry<K, V> first = tab[index];
+            HashEntry<K, V> e = first;
+            // a ref remove operation compares the Reference instance
+            while (e != null && key != e.keyRef && (refRemove || hash != e.hash || !keyEq(key, e.key()))) {
+                e = e.next;
+            }
+
+            V oldValue = null;
+            if (e != null) {
+                final V v = e.value();
+                if (value == null || value.equals(v)) {
+                    oldValue = v;
+                    // All entries following removed node can stay
+                    // in list, but all preceding ones need to be
+                    // cloned.
+                    ++modCount;
+                    HashEntry<K, V> newFirst = e.next;
+                    for (HashEntry<K, V> p = first; p != e; p = p.next) {
+                        final K pKey = p.key();
+                        // Skip GC'd keys
+                        if (pKey == null) {
+                            c--;
+                            continue;
+                        }
+                        newFirst = newHashEntry(pKey, p.hash, newFirst, p.value());
+                    }
+                    tab[index] = newFirst;
+                    // write-volatile
+                    count = c;
+                }
+            }
+            return oldValue;
+        }
+
+        void removeStale() {
+            KeyReference ref;
+            while ((ref = (KeyReference) refQueue.poll()) != null) {
+                remove(ref.keyRef(), ref.keyHash(), null, true);
+            }
+        }
+
+        V replace(final K key, final int hash, final V newValue) {
+            lock();
+            try {
+                return replaceInternal(key, hash, newValue);
+            } finally {
+                unlock();
+            }
+        }
+
+        boolean replace(final K key, final int hash, final V oldValue, final V newValue) {
+            lock();
+            try {
+                return replaceInternal2(key, hash, oldValue, newValue);
+            } finally {
+                unlock();
+            }
+        }
+
+        private V replaceInternal(final K key, final int hash, final V newValue) {
+            removeStale();
+            HashEntry<K, V> e = getFirst(hash);
+            while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
+                e = e.next;
+            }
+            V oldValue = null;
+            if (e != null) {
+                oldValue = e.value();
+                e.setValue(newValue, valueType, refQueue);
+            }
+            return oldValue;
+        }
+
+        private boolean replaceInternal2(final K key, final int hash, final V oldValue, final V newValue) {
+            removeStale();
+            HashEntry<K, V> e = getFirst(hash);
+            while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
+                e = e.next;
+            }
+            boolean replaced = false;
+            if (e != null && oldValue.equals(e.value())) {
+                replaced = true;
+                e.setValue(newValue, valueType, refQueue);
+            }
+            return replaced;
+        }
+
+        /**
+         * Sets table to new HashEntry array. Call only while holding lock or in constructor.
+         */
+        void setTable(final HashEntry<K, V>[] newTable) {
+            threshold = (int) (newTable.length * loadFactor);
+            table = newTable;
+            refQueue = new ReferenceQueue<>();
+        }
+    }
+
+    private static class SimpleEntry<K, V> implements Entry<K, V> {
+
+        private static boolean eq(final Object o1, final Object o2) {
+            return o1 == null ? o2 == null : o1.equals(o2);
+        }
+
+        private final K key;
+
+        private V value;
+
+        SimpleEntry(final K key, final V value) {
+            this.key = key;
+            this.value = value;
+        }
+
+        @Override
+        public boolean equals(final Object o) {
+            if (!(o instanceof Map.Entry)) {
+                return false;
+            }
+            final Entry<?, ?> e = (Entry<?, ?>) o;
+            return eq(key, e.getKey()) && eq(value, e.getValue());
+        }
+
+        @Override
+        public K getKey() {
+            return key;
+        }
+
+        @Override
+        public V getValue() {
+            return value;
+        }
+
+        @Override
+        public int hashCode() {
+            return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
+        }
+
+        @Override
+        public V setValue(final V value) {
+            final V oldValue = this.value;
+            this.value = value;
+            return oldValue;
+        }
+
+        @Override
+        public String toString() {
+            return key + "=" + value;
+        }
+    }
+
+    /**
+     * A soft-key reference which stores the key hash needed for reclamation.
+     */
+    private static final class SoftKeyReference<K> extends SoftReference<K> implements KeyReference {
+
+        private final int hash;
+
+        SoftKeyReference(final K key, final int hash, final ReferenceQueue<Object> refQueue) {
+            super(key, refQueue);
+            this.hash = hash;
+        }
+
+        @Override
+        public int keyHash() {
+            return hash;
+        }
+
+        @Override
+        public Object keyRef() {
+            return this;
+        }
+    }
+
+    private static final class SoftValueReference<V> extends SoftReference<V> implements KeyReference {
+        private final Object keyRef;
+        private final int hash;
+
+        SoftValueReference(final V value, final Object keyRef, final int hash, final ReferenceQueue<Object> refQueue) {
+            super(value, refQueue);
+            this.keyRef = keyRef;
+            this.hash = hash;
+        }
+
+        @Override
+        public int keyHash() {
+            return hash;
+        }
+
+        @Override
+        public Object keyRef() {
+            return keyRef;
+        }
+    }
+
+    private final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
+        @Override
+        public V next() {
+            return super.nextEntry().value();
+        }
+
+        @Override
+        public V nextElement() {
+            return super.nextEntry().value();
+        }
+    }
+
+    private final class Values extends AbstractCollection<V> {
+        @Override
+        public void clear() {
+            ConcurrentReferenceHashMap.this.clear();
+        }
+
+        @Override
+        public boolean contains(final Object o) {
+            return ConcurrentReferenceHashMap.this.containsValue(o);
+        }
+
+        @Override
+        public boolean isEmpty() {
+            return ConcurrentReferenceHashMap.this.isEmpty();
+        }
+
+        @Override
+        public Iterator<V> iterator() {
+            return new ValueIterator();
+        }
+
+        @Override
+        public int size() {
+            return ConcurrentReferenceHashMap.this.size();
+        }
+    }
+
+    /**
+     * A weak-key reference which stores the key hash needed for reclamation.
+     */
+    private static final class WeakKeyReference<K> extends WeakReference<K> implements KeyReference {
+        private final int hash;
+
+        WeakKeyReference(final K key, final int hash, final ReferenceQueue<Object> refQueue) {
+            super(key, refQueue);
+            this.hash = hash;
+        }
+
+        @Override
+        public int keyHash() {
+            return hash;
+        }
+
+        @Override
+        public Object keyRef() {
+            return this;
+        }
+    }
+
+    private static final class WeakValueReference<V> extends WeakReference<V> implements KeyReference {
+        private final Object keyRef;
+        private final int hash;
+
+        WeakValueReference(final V value, final Object keyRef, final int hash, final ReferenceQueue<Object> refQueue) {
+            super(value, refQueue);
+            this.keyRef = keyRef;
+            this.hash = hash;
+        }
+
+        @Override
+        public int keyHash() {
+            return hash;
+        }
+
+        @Override
+        public Object keyRef() {
+            return keyRef;
+        }
+    }
+
+    /**
+     * Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying map.
+     */
+    private final class WriteThroughEntry extends SimpleEntry<K, V> {
+
+        private WriteThroughEntry(final K k, final V v) {
+            super(k, v);
+        }
+
+        /**
+         * Set our entry's value and writes it through to the map. The value to return is somewhat arbitrary: since a WriteThroughEntry does not necessarily
+         * track asynchronous changes, the most recent "previous" value could be different from what we return (or could even have been removed in which case
+         * the put will re-establish). We do not and cannot guarantee more.
+         */
+        @Override
+        public V setValue(final V value) {
+            if (value == null) {
+                throw new NullPointerException();
+            }
+            final V v = super.setValue(value);
+            ConcurrentReferenceHashMap.this.put(getKey(), value);
+            return v;
+        }
+    }
+
+    static final ReferenceType DEFAULT_KEY_TYPE = ReferenceType.WEAK;
+
+    static final ReferenceType DEFAULT_VALUE_TYPE = ReferenceType.STRONG;
+
+    static final EnumSet<Option> DEFAULT_OPTIONS = null;
+
+    /**
+     * The default initial capacity for this table, used when not otherwise specified in a constructor.
+     */
+    static final int DEFAULT_INITIAL_CAPACITY = 16;
+
+    /**
+     * The default load factor for this table, used when not otherwise specified in a constructor.
+     */
+    static final float DEFAULT_LOAD_FACTOR = 0.75f;
+
+    /**
+     * The default concurrency level for this table, used when not otherwise specified in a constructor.
+     */
+    static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+
+    /**
+     * The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments. MUST be a power of two &lt;=
+     * 1&lt;&lt;30 to ensure that entries are indexable using ints.
+     */
+    private static final int MAXIMUM_CAPACITY = 1 << 30;
+
+    /**
+     * The maximum number of segments to allow; used to bound constructor arguments.
+     */
+    private static final int MAX_SEGMENTS = 1 << 16;
+
+    /**
+     * Number of unsynchronized retries in size and containsValue methods before resorting to locking. This is used to avoid unbounded retries if tables undergo
+     * continuous modification which would make it impossible to obtain an accurate result.
+     */
+    private static final int RETRIES_BEFORE_LOCK = 2;
+
+    /**
+     * Creates a new Builder.
+     * <p>
+     * By default, keys are weak, and values are strong.
+     * </p>
+     * <p>
+     * The default values are:
+     * </p>
+     * <ul>
+     * <li>concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}</li>
+     * <li>initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}</li>
+     * <li>key reference type: {@link ReferenceType#WEAK}</li>
+     * <li>load factor: {@value #DEFAULT_LOAD_FACTOR}</li>
+     * <li>options: {@code null}</li>
+     * <li>source map: {@code null}</li>
+     * <li>value reference type: {@link ReferenceType#STRONG}</li>
+     * </ul>
+     *
+     * @param <K> the type of keys.
+     * @param <V> the type of values.
+     * @return a new Builder.
+     */
+    public static <K, V> Builder<K, V> builder() {
+        return new Builder<>();
+    }
+
+    /**
+     * Applies a supplemental hash function to a given hashCode, which defends against poor quality hash functions. This is critical because
+     * ConcurrentReferenceHashMap uses power-of-two length hash tables, that otherwise encounter collisions for hashCodes that do not differ in lower or upper
+     * bits.
+     */
+    private static int hash(int h) {
+        // Spread bits to regularize both segment and index locations,
+        // using variant of single-word Wang/Jenkins hash.
+        h += h << 15 ^ 0xffffcd7d;
+        h ^= h >>> 10;
+        h += h << 3;
+        h ^= h >>> 6;
+        h += (h << 2) + (h << 14);
+        return h ^ h >>> 16;
+    }
+
+    /**
+     * Mask value for indexing into segments. The upper bits of a key's hash code are used to choose the segment.
+     */
+    private final int segmentMask;
+
+    /**
+     * Shift value for indexing within segments.
+     */
+    private final int segmentShift;
+
+    /**
+     * The segments, each of which is a specialized hash table
+     */
+    private final Segment<K, V>[] segments;
+
+    private final boolean identityComparisons;
+
+    private transient Set<K> keySet;
+
+    private transient Set<Entry<K, V>> entrySet;
+
+    private transient Collection<V> values;
+
+    /**
+     * Creates a new, empty map with the specified initial capacity, reference types, load factor, and concurrency level.
+     * <p>
+     * Behavioral changing options such as {@link Option#IDENTITY_COMPARISONS} can also be specified.
+     * </p>
+     *
+     * @param initialCapacity  the initial capacity. The implementation performs internal sizing to accommodate this many elements.
+     * @param loadFactor       the load factor threshold, used to control resizing. Resizing may be performed when the average number of elements per bin
+     *                         exceeds this threshold.
+     * @param concurrencyLevel the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this
+     *                         many threads.
+     * @param keyType          the reference type to use for keys.
+     * @param valueType        the reference type to use for values.
+     * @param options          the behavioral options.
+     * @throws IllegalArgumentException if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
+     */
+    private ConcurrentReferenceHashMap(int initialCapacity, final float loadFactor, int concurrencyLevel, final ReferenceType keyType,
+            final ReferenceType valueType, final EnumSet<Option> options) {
+        if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) {
+            throw new IllegalArgumentException();
+        }
+        if (concurrencyLevel > MAX_SEGMENTS) {
+            concurrencyLevel = MAX_SEGMENTS;
+        }
+        // Find power-of-two sizes best matching arguments
+        int sshift = 0;
+        int ssize = 1;
+        while (ssize < concurrencyLevel) {
+            ++sshift;
+            ssize <<= 1;
+        }
+        segmentShift = 32 - sshift;
+        segmentMask = ssize - 1;
+        this.segments = Segment.newArray(ssize);
+        if (initialCapacity > MAXIMUM_CAPACITY) {
+            initialCapacity = MAXIMUM_CAPACITY;
+        }
+        int c = initialCapacity / ssize;
+        if (c * ssize < initialCapacity) {
+            ++c;
+        }
+        int cap = 1;
+        while (cap < c) {
+            cap <<= 1;
+        }
+        identityComparisons = options != null && options.contains(Option.IDENTITY_COMPARISONS);
+        for (int i = 0; i < this.segments.length; ++i) {
+            this.segments[i] = new Segment<>(cap, loadFactor, keyType, valueType, identityComparisons);
+        }
+    }
+
+    /**
+     * Removes all of the mappings from this map.
+     */
+    @Override
+    public void clear() {
+        for (final Segment<K, V> segment : segments) {
+            segment.clear();
+        }
+    }
+
+    @Override
+    public V compute(final K key, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+        Objects.requireNonNull(key);
+        Objects.requireNonNull(remappingFunction);
+
+        final int hash = hashOf(key);
+        final Segment<K, V> segment = segmentFor(hash);
+        return segment.apply(key, hash, remappingFunction);
+    }
+
+    /**
+     * The default implementation is equivalent to the following steps for this {@code map}, then returning the current value or {@code null} if now absent:
+     *
+     * <pre>{@code
+     * if (map.get(key) == null) {
+     *     V newValue = mappingFunction.apply(key);
+     *     if (newValue != null)
+     *         return map.putIfAbsent(key, newValue);
+     * }
+     * }</pre>
+     * <p>
+     * The default implementation may retry these steps when multiple threads attempt updates including potentially calling the mapping function multiple times.
+     * </p>
+     * <p>
+     * This implementation assumes that the ConcurrentMap cannot contain null values and {@code get()} returning null unambiguously means the key is absent.
+     * Implementations which support null values <strong>must</strong> override this default implementation.
+     * </p>
+     */
+    @Override
+    public V computeIfAbsent(final K key, final Function<? super K, ? extends V> mappingFunction) {
+        Objects.requireNonNull(key);
+        Objects.requireNonNull(mappingFunction);
+
+        final int hash = hashOf(key);
+        final Segment<K, V> segment = segmentFor(hash);
+        final V v = segment.get(key, hash);
+        return v == null ? segment.put(key, hash, null, mappingFunction, true) : v;
+    }
+
+    @Override
+    public V computeIfPresent(final K key, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+        Objects.requireNonNull(key);
+        Objects.requireNonNull(remappingFunction);
+
+        final int hash = hashOf(key);
+        final Segment<K, V> segment = segmentFor(hash);
+        final V v = segment.get(key, hash);
+        if (v == null) {
+            return null;
+        }
+
+        return segmentFor(hash).applyIfPresent(key, hash, remappingFunction);
+    }
+
+    /**
+     * Tests if the specified object is a key in this table.
+     *
+     * @param key possible key
+     * @return {@code true} if and only if the specified object is a key in this table, as determined by the {@code equals} method; {@code false} otherwise.
+     * @throws NullPointerException if the specified key is null
+     */
+    @Override
+    public boolean containsKey(final Object key) {
+        final int hash = hashOf(key);
+        return segmentFor(hash).containsKey(key, hash);
+    }
+
+    /**
+     * Returns {@code true} if this map maps one or more keys to the specified value. Note: This method requires a full internal traversal of the hash table,
+     * therefore it is much slower than the method {@code containsKey}.
+     *
+     * @param value value whose presence in this map is to be tested
+     * @return {@code true} if this map maps one or more keys to the specified value
+     * @throws NullPointerException if the specified value is null
+     */
+    @Override
+    public boolean containsValue(final Object value) {
+        if (value == null) {
+            throw new NullPointerException();
+        }
+        // See explanation of modCount use above
+        final Segment<K, V>[] segments = this.segments;
+        final int[] mc = new int[segments.length];
+        // Try a few times without locking
+        for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
+            // final int sum = 0;
+            int mcsum = 0;
+            for (int i = 0; i < segments.length; ++i) {
+                // final int c = segments[i].count;
+                mcsum += mc[i] = segments[i].modCount;
+                if (segments[i].containsValue(value)) {
+                    return true;
+                }
+            }
+            boolean cleanSweep = true;
+            if (mcsum != 0) {
+                for (int i = 0; i < segments.length; ++i) {
+                    // final int c = segments[i].count;
+                    if (mc[i] != segments[i].modCount) {
+                        cleanSweep = false;
+                        break;
+                    }
+                }
+            }
+            if (cleanSweep) {
+                return false;
+            }
+        }
+        // Resort to locking all segments
+        for (final Segment<K, V> segment : segments) {
+            segment.lock();
+        }
+        boolean found = false;
+        try {
+            for (final Segment<K, V> segment : segments) {
+                if (segment.containsValue(value)) {
+                    found = true;
+                    break;
+                }
+            }
+        } finally {
+            for (final Segment<K, V> segment : segments) {
+                segment.unlock();
+            }
+        }
+        return found;
+    }
+
+    /**
+     * Returns a {@link Set} view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and
+     * vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the {@code Iterator.remove}, {@code Set.remove},
+     * {@code removeAll}, {@code retainAll}, and {@code clear} operations. It does not support the {@code add} or {@code addAll} operations.
+     * <p>
+     * The view's {@code iterator} is a "weakly consistent" iterator that will never throw {@link ConcurrentModificationException}, and is guaranteed to
+     * traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to
+     * construction.
+     * </p>
+     */
+    @Override
+    public Set<Entry<K, V>> entrySet() {
+        final Set<Entry<K, V>> es = entrySet;
+        return es != null ? es : (entrySet = new EntrySet(false));
+    }
+
+    /**
+     * Returns the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key.
+     * <p>
+     * If this map contains a mapping from a key {@code k} to a value {@code v} such that {@code key.equals(k)}, then this method returns {@code v}; otherwise
+     * it returns {@code null}. (There can be at most one such mapping.)
+     * </p>
+     *
+     * @throws NullPointerException if the specified key is null
+     */
+    @Override
+    public V get(final Object key) {
+        final int hash = hashOf(key);
+        return segmentFor(hash).get(key, hash);
+    }
+
+    private int hashOf(final Object key) {
+        return hash(identityComparisons ? System.identityHashCode(key) : key.hashCode());
+    }
+
+    /**
+     * Returns {@code true} if this map contains no key-value mappings.
+     *
+     * @return {@code true} if this map contains no key-value mappings
+     */
+    @Override
+    public boolean isEmpty() {
+        final Segment<K, V>[] segments = this.segments;
+        //
+        // We keep track of per-segment modCounts to avoid ABA problems in which an element in one segment was added and in another removed during traversal, in
+        // which case the table was never actually empty at any point. Note the similar use of modCounts in the size() and containsValue() methods, which are
+        // the only other methods also susceptible to ABA problems.
+        //
+        final int[] mc = new int[segments.length];
+        int mcsum = 0;
+        for (int i = 0; i < segments.length; ++i) {
+            if (segments[i].count != 0) {
+                return false;
+            }
+            mcsum += mc[i] = segments[i].modCount;
+        }
+        // If mcsum happens to be zero, then we know we got a snapshot
+        // before any modifications at all were made. This is
+        // probably common enough to bother tracking.
+        if (mcsum != 0) {
+            for (int i = 0; i < segments.length; ++i) {
+                if (segments[i].count != 0 || mc[i] != segments[i].modCount) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Returns a {@link Set} view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and
+     * vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the {@code Iterator.remove}, {@code Set.remove},
+     * {@code removeAll}, {@code retainAll}, and {@code clear} operations. It does not support the {@code add} or {@code addAll} operations.
+     * <p>
+     * The view's {@code iterator} is a "weakly consistent" iterator that will never throw {@link ConcurrentModificationException}, and guarantees to traverse
+     * elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
+     * </p>
+     */
+    @Override
+    public Set<K> keySet() {
+        final Set<K> ks = keySet;
+        return ks != null ? ks : (keySet = new KeySet());
+    }
+
+    /**
+     * Removes any stale entries whose keys have been finalized. Use of this method is normally not necessary since stale entries are automatically removed
+     * lazily, when blocking operations are required. However, there are some cases where this operation should be performed eagerly, such as cleaning up old
+     * references to a ClassLoader in a multi-classloader environment.
+     * <p>
+     * Note: this method will acquire locks one at a time across all segments of this table, so this method should be used sparingly.
+     * </p>
+     */
+    public void purgeStaleEntries() {
+        for (final Segment<K, V> segment : segments) {
+            segment.removeStale();
+        }
+    }
+
+    /**
+     * Maps the specified key to the specified value in this table. Neither the key nor the value can be null.
+     * <p>
+     * The value can be retrieved by calling the {@code get} method with a key that is equal to the original key.
+     * </p>
+     *
+     * @param key   key with which the specified value is to be associated
+     * @param value value to be associated with the specified key
+     * @return the previous value associated with {@code key}, or {@code null} if there was no mapping for {@code key}
+     * @throws NullPointerException if the specified key or value is null
+     */
+    @Override
+    public V put(final K key, final V value) {
+        if (key == null || value == null) {
+            throw new NullPointerException();
+        }
+        final int hash = hashOf(key);
+        return segmentFor(hash).put(key, hash, value, null, false);
+    }
+
+    /**
+     * Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the
+     * specified map.
+     *
+     * @param m mappings to be stored in this map
+     */
+    @Override
+    public void putAll(final Map<? extends K, ? extends V> m) {
+        for (final Entry<? extends K, ? extends V> e : m.entrySet()) {
+            put(e.getKey(), e.getValue());
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @return the previous value associated with the specified key, or {@code null} if there was no mapping for the key
+     * @throws NullPointerException if the specified key or value is null
+     */
+    @Override
+    public V putIfAbsent(final K key, final V value) {
+        if (value == null) {
+            throw new NullPointerException();
+        }
+        final int hash = hashOf(key);
+        return segmentFor(hash).put(key, hash, value, null, true);
+    }
+
+    /**
+     * Removes the key (and its corresponding value) from this map. This method does nothing if the key is not in the map.
+     *
+     * @param key the key that needs to be removed
+     * @return the previous value associated with {@code key}, or {@code null} if there was no mapping for {@code key}
+     * @throws NullPointerException if the specified key is null
+     */
+    @Override
+    public V remove(final Object key) {
+        final int hash = hashOf(key);
+        return segmentFor(hash).remove(key, hash, null, false);
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @throws NullPointerException if the specified key is null
+     */
+    @Override
+    public boolean remove(final Object key, final Object value) {
+        final int hash = hashOf(key);
+        if (value == null) {
+            return false;
+        }
+        return segmentFor(hash).remove(key, hash, value, false) != null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @return the previous value associated with the specified key, or {@code null} if there was no mapping for the key
+     * @throws NullPointerException if the specified key or value is null
+     */
+    @Override
+    public V replace(final K key, final V value) {
+        if (value == null) {
+            throw new NullPointerException();
+        }
+        final int hash = hashOf(key);
+        return segmentFor(hash).replace(key, hash, value);
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @throws NullPointerException if any of the arguments are null
+     */
+    @Override
+    public boolean replace(final K key, final V oldValue, final V newValue) {
+        if (oldValue == null || newValue == null) {
+            throw new NullPointerException();
+        }
+        final int hash = hashOf(key);
+        return segmentFor(hash).replace(key, hash, oldValue, newValue);
+    }
+
+    /**
+     * Returns the segment that should be used for key with given hash
+     *
+     * @param hash the hash code for the key
+     * @return the segment
+     */
+    private Segment<K, V> segmentFor(final int hash) {
+        return segments[hash >>> segmentShift & segmentMask];
+    }
+
+    /**
+     * Returns the number of key-value mappings in this map. If the map contains more than {@code Integer.MAX_VALUE} elements, returns
+     * {@code Integer.MAX_VALUE}.
+     *
+     * @return the number of key-value mappings in this map
+     */
+    @Override
+    public int size() {
+        final Segment<K, V>[] segments = this.segments;
+        long sum = 0;
+        long check = 0;
+        final int[] mc = new int[segments.length];
+        // Try a few times to get accurate count. On failure due to
+        // continuous async changes in table, resort to locking.
+        for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
+            check = 0;
+            sum = 0;
+            int mcsum = 0;
+            for (int i = 0; i < segments.length; ++i) {
+                sum += segments[i].count;
+                mcsum += mc[i] = segments[i].modCount;
+            }
+            if (mcsum != 0) {
+                for (int i = 0; i < segments.length; ++i) {
+                    check += segments[i].count;
+                    if (mc[i] != segments[i].modCount) {
+                        // force retry
+                        check = -1;
+                        break;
+                    }
+                }
+            }
+            if (check == sum) {
+                break;
+            }
+        }
+        if (check != sum) {
+            // Resort to locking all segments
+            sum = 0;
+            for (final Segment<K, V> segment : segments) {
+                segment.lock();
+            }
+            for (final Segment<K, V> segment : segments) {
+                sum += segment.count;
+            }
+            for (final Segment<K, V> segment : segments) {
+                segment.unlock();
+            }
+        }
+        return sum > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) sum;
+    }
+
+    /**
+     * Returns a {@link Collection} view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the
+     * collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the
+     * {@code Iterator.remove}, {@code Collection.remove}, {@code removeAll}, {@code retainAll}, and {@code clear} operations. It does not support the
+     * {@code add} or {@code addAll} operations.
+     * <p>
+     * The view's {@code iterator} is a "weakly consistent" iterator that will never throw {@link ConcurrentModificationException}, and guarantees to traverse
+     * elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
+     * </p>
+     */
+    @Override
+    public Collection<V> values() {
+        final Collection<V> vs = values;
+        return vs != null ? vs : (values = new Values());
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/AbstractConcurrentReferenceHashMapTest.java b/src/test/java/org/apache/commons/collections4/map/AbstractConcurrentReferenceHashMapTest.java
new file mode 100644
index 000000000..97b57eb65
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/AbstractConcurrentReferenceHashMapTest.java
@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.EnumSet;
+
+import org.apache.commons.collections4.map.ConcurrentReferenceHashMap.Option;
+
+/**
+ * Tests {@link ConcurrentReferenceHashMap}.
+ *
+ * @param <K> the key type.
+ * @param <V> the value type.
+ */
+public abstract class AbstractConcurrentReferenceHashMapTest<K, V> extends AbstractMapTest<K, V> {
+
+    protected static final EnumSet<Option> IDENTITY_COMPARISONS = EnumSet.of(Option.IDENTITY_COMPARISONS);
+
+    public AbstractConcurrentReferenceHashMapTest() {
+        super(AbstractConcurrentReferenceHashMapTest.class.getSimpleName());
+    }
+
+    @Override
+    public boolean isAllowNullKey() {
+        return false;
+    }
+
+    @Override
+    public boolean isAllowNullValueGet() {
+        return false;
+    }
+
+    @Override
+    public boolean isAllowNullValuePut() {
+        return false;
+    }
+
+    @Override
+    public boolean isTestSerialization() {
+        return false;
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentHashMapSanityTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentHashMapSanityTest.java
new file mode 100644
index 000000000..f50dba71d
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentHashMapSanityTest.java
@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A sanity test for the test framework.
+ *
+ * @param <K> the key type.
+ * @param <V> the value type.
+ */
+public class ConcurrentHashMapSanityTest<K, V> extends AbstractMapTest<K, V> {
+
+    public ConcurrentHashMapSanityTest() {
+        super(ConcurrentHashMapSanityTest.class.getSimpleName());
+    }
+
+    @Override
+    public boolean isAllowNullKey() {
+        return false;
+    }
+
+    @Override
+    public boolean isAllowNullValueGet() {
+        return false;
+    }
+
+    @Override
+    public boolean isAllowNullValuePut() {
+        return false;
+    }
+
+    /**
+     * Don't test, just a sanity check for the test framework.
+     */
+    @Override
+    public boolean isTestSerialization() {
+        return false;
+    }
+
+    @Override
+    public Map<K, V> makeObject() {
+        return new ConcurrentHashMap<>();
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapDefaultsTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapDefaultsTest.java
new file mode 100644
index 000000000..a1620b118
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapDefaultsTest.java
@@ -0,0 +1,31 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapDefaultsTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // The default behavior
+        return ConcurrentReferenceHashMap.<K, V>builder().get();
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftIdCTest.java
new file mode 100644
index 000000000..5115dc3c2
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVSoftIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .softKeys()
+            .softValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftTest.java
new file mode 100644
index 000000000..e22ca32a6
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVSoftTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .softKeys()
+            .softValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongIdCTest.java
new file mode 100644
index 000000000..6725a712b
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVStrongIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .softKeys()
+            .strongValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongTest.java
new file mode 100644
index 000000000..e42b78975
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVStrongTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .softKeys()
+            .strongValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakIdCTest.java
new file mode 100644
index 000000000..90a29d02d
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVWeakIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .softKeys()
+            .weakValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakTest.java
new file mode 100644
index 000000000..b53b2409e
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVWeakTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .softKeys()
+            .weakValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftIdCTest.java
new file mode 100644
index 000000000..c824e6cea
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVSoftIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .strongKeys()
+            .softValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftTest.java
new file mode 100644
index 000000000..2d6291273
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVSoftTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .strongKeys()
+            .softValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongIdCTest.java
new file mode 100644
index 000000000..40c1fc019
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVStrongIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .strongKeys()
+            .strongValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongTest.java
new file mode 100644
index 000000000..49148901d
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVStrongTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .strongKeys()
+            .strongValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakIdCTest.java
new file mode 100644
index 000000000..9cb77a40f
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVWeakIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .strongKeys()
+            .weakValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakTest.java
new file mode 100644
index 000000000..b6c9abb92
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVWeakTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .strongKeys()
+            .weakValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftIdCTest.java
new file mode 100644
index 000000000..8d3cb9b62
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVSoftIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .weakKeys()
+            .softValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftTest.java
new file mode 100644
index 000000000..20ed8b865
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVSoftTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .weakKeys()
+            .softValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongIdCTest.java
new file mode 100644
index 000000000..3920af28a
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVStrongIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .weakKeys()
+            .strongValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongTest.java
new file mode 100644
index 000000000..f8ae54b2b
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVStrongTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .weakKeys()
+            .strongValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakIdCTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakIdCTest.java
new file mode 100644
index 000000000..7c7db04fe
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVWeakIdCTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .weakKeys()
+            .weakValues()
+            .setOptions(IDENTITY_COMPARISONS)
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakTest.java
new file mode 100644
index 000000000..867ea2b69
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakTest.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVWeakTest<K, V> extends AbstractConcurrentReferenceHashMapTest<K, V> {
+
+    @Override
+    public Map<K, V> makeObject() {
+        // @formatter:off
+        return ConcurrentReferenceHashMap.<K, V>builder()
+            .weakKeys()
+            .weakValues()
+            .get();
+        // @formatter:on
+    }
+
+}
diff --git a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapTest.java b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapTest.java
new file mode 100644
index 000000000..08f47162e
--- /dev/null
+++ b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapTest.java
@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.collections4.map;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.commons.collections4.map.ConcurrentReferenceHashMap.Option;
+import org.apache.commons.collections4.map.ConcurrentReferenceHashMap.ReferenceType;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link ConcurrentReferenceHashMap}.
+ */
+public class ConcurrentReferenceHashMapTest {
+
+    @Test
+    public void testBuilderAll() {
+        final Map<Integer, String> map0 = new HashMap<>();
+        map0.put(1, "1");
+        // @formatter:off
+        final Map<Integer, String> map = ConcurrentReferenceHashMap.<Integer, String>builder()
+                .setConcurrencyLevel(4)
+                .setInitialCapacity(32)
+                .setKeyReferenceType(ReferenceType.SOFT)
+                .setLoadFactor(0.74f)
+                .setOptions(EnumSet.of(Option.IDENTITY_COMPARISONS))
+                .setSourceMap(map0)
+                .get();
+        // @formatter:on
+        map0.put(2, "2");
+        assertTrue(map.containsKey(1));
+        assertFalse(map.containsKey(2));
+
+    }
+}