BAEL-6600 - limit max size by LinkedHashMap and custom HashMap

core-java-modules/core-java-collections-maps-7/src/main/java/com/baeldung/map/HashMapWithMaxSizeLimit.java

@@ -0,0 +1,25 @@
+package com.baeldung.map;
+
+import java.util.HashMap;
+
+public class HashMapWithMaxSizeLimit<K, V> extends HashMap<K, V> {
+
+    private static final long serialVersionUID = 1L;
+
+    private int maxSize = -1;
+    
+   
+    public HashMapWithMaxSizeLimit(int maxSize) {
+        super();
+        this.maxSize = maxSize;
+    }
+
+
+    public V putWithLimit(K key, V value) throws Exception {
+        if (this.maxSize != - 1 && this.size() >= this.maxSize && !this.containsKey(key)) {
+            throw new Exception("Max size exceeded!");
+        }
+        return this.put(key, value);
+    }
+
+}

core-java-modules/core-java-collections-maps-7/src/test/java/com/baeldung/map/LimitMaxSizeHashMapByCustomHashMapUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.map;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class LimitMaxSizeHashMapByCustomHashMapUnitTest {
+
+    private final int MAX_SIZE = 4;
+    private LinkedHashMap<Integer, String> linkedHashMap;
+
+    @BeforeEach
+    void setUp() {
+        linkedHashMap = new LinkedHashMap<Integer, String>() {
+            private static final long serialVersionUID = 1L;
+
+            protected boolean removeEldestEntry(Map.Entry<Integer, String> eldest) {
+                return size() > MAX_SIZE;
+            }
+        };
+        linkedHashMap.put(1, "One");
+        linkedHashMap.put(2, "Two");
+        linkedHashMap.put(3, "Three");
+        linkedHashMap.put(4, "Four");
+    }
+
+    @Test
+    void givenLinkedHashMapObject_whenAddingNewEntry_thenEldestEntryIsRemoved() {
+        linkedHashMap.put(5, "Five");
+        String[] expectedArrayAfterFive = { "Two", "Three", "Four", "Five" };
+        assertArrayEquals(expectedArrayAfterFive, linkedHashMap.values()
+            .toArray());
+        linkedHashMap.put(6, "Six");
+        String[] expectedArrayAfterSix = { "Three", "Four", "Five", "Six" };
+        assertArrayEquals(expectedArrayAfterSix, linkedHashMap.values()
+            .toArray());
+    }
+
+}

core-java-modules/core-java-collections-maps-7/src/test/java/com/baeldung/map/LimitMaxSizeHashMapByLinkedHashMapUnitTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.map;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class LimitMaxSizeHashMapByLinkedHashMapUnitTest {
+
+    private final int MAX_SIZE = 4;
+    private HashMapWithMaxSizeLimit<Integer, String> hashMapWithMaxSizeLimit;
+
+    @BeforeEach
+    void setUp() {
+        hashMapWithMaxSizeLimit = new HashMapWithMaxSizeLimit<Integer, String>(MAX_SIZE);
+    }
+
+    @Test
+    void givenCustomHashMapObject_whenAddingNewEntryAndLimitExceeded_thenThrowsException() {
+        Exception exception = assertThrows(Exception.class, () -> {
+            hashMapWithMaxSizeLimit.putWithLimit(1, "One");
+            hashMapWithMaxSizeLimit.putWithLimit(2, "Two");
+            hashMapWithMaxSizeLimit.putWithLimit(3, "Three");
+            hashMapWithMaxSizeLimit.putWithLimit(4, "Four");
+            hashMapWithMaxSizeLimit.putWithLimit(5, "Five");
+        });
+
+        String messageThrownWhenSizeExceedsLimit = "Max size exceeded!";
+        String actualMessage = exception.getMessage();
+
+        assertTrue(actualMessage.equals(messageThrownWhenSizeExceedsLimit));
+    }
+
+}