Add DefaultedMap that returns a default value if the key is not in the map
RFE 30911, by Rafael U. C. Afonso git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/collections/trunk@158692 13f79535-47bb-0310-9956-ffa450edef68
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Stephen Colebourne
parent
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@ -38,6 +38,7 @@ There are no new deprecations.
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<center><h3>NEW CLASSES</h3></center>
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<ul>
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<li>DefaultedMap - Returns a default value when the key is not found, without adding the default value to the map itself [30911]</li>
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<li>LoopingListIterator - When the end of the list is reached the iteration continues from the start [30166]</li>
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</ul>
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@ -0,0 +1,189 @@
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/*
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* Copyright 2005 The Apache Software Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.commons.collections.map;
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import java.io.IOException;
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import java.io.ObjectInputStream;
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import java.io.ObjectOutputStream;
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import java.io.Serializable;
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import java.util.HashMap;
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import java.util.Map;
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import org.apache.commons.collections.Factory;
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import org.apache.commons.collections.Transformer;
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import org.apache.commons.collections.functors.ConstantTransformer;
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import org.apache.commons.collections.functors.FactoryTransformer;
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/**
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* Decorates another <code>Map</code> returning a default value if the map
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* does not contain the requested key.
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* <p>
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* When the {@link #get(Object)} method is called with a key that does not
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* exist in the map, this map will return the default value specified in
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* the constructor/factory. Only the get method is altered, so the
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* {@link Map#containsKey(Object)} can be used to determine if a key really
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* is in the map or not.
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* <p>
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* The defaulted value is not added to the map.
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* Compare this behaviour with {@link LazyMap}, which does add the value
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* to the map (via a Transformer).
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* <p>
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* For instance:
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* <pre>
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* Map map = new DefaultedMap("NULL");
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* Object obj = map.get("Surname");
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* // obj == "NULL"
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* </pre>
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* After the above code is executed the map is still empty.
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*
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* @since Commons Collections 3.2
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* @version $Revision: 1.7 $ $Date$
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*
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* @author Stephen Colebourne
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* @author Rafael U.C. Afonso
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* @see LazyMap
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*/
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public class DefaultedMap
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extends AbstractMapDecorator
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implements Map, Serializable {
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/** Serialization version */
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private static final long serialVersionUID = 19698628745827L;
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/** The transformer to use if the map does not contain a key */
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protected final Object value;
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//-----------------------------------------------------------------------
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/**
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* Factory method to create a defaulting map.
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* <p>
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* The value specified is returned when a missing key is found.
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*
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* @param map the map to decorate, must not be null
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* @param defaultValue the default value to return when the key is not found
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* @throws IllegalArgumentException if map is null
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*/
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public static Map decorate(Map map, Object defaultValue) {
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if (defaultValue instanceof Transformer) {
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defaultValue = ConstantTransformer.getInstance(defaultValue);
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}
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return new DefaultedMap(map, defaultValue);
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}
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/**
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* Factory method to create a defaulting map.
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* <p>
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* The factory specified is called when a missing key is found.
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* The result will be returned as the result of the map get(key) method.
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*
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* @param map the map to decorate, must not be null
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* @param factory the factory to use, must not be null
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* @throws IllegalArgumentException if map or factory is null
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*/
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public static Map decorate(Map map, Factory factory) {
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if (factory == null) {
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throw new IllegalArgumentException("Factory must not be null");
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}
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return new DefaultedMap(map, FactoryTransformer.getInstance(factory));
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}
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/**
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* Factory method to create a defaulting map.
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* <p>
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* The transformer specified is called when a missing key is found.
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* The key is passed to the transformer as the input, and the result
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* will be returned as the result of the map get(key) method.
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*
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* @param map the map to decorate, must not be null
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* @param factory the factory to use, must not be null
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* @throws IllegalArgumentException if map or factory is null
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*/
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public static Map decorate(Map map, Transformer factory) {
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if (factory == null) {
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throw new IllegalArgumentException("Transformer must not be null");
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}
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return new DefaultedMap(map, factory);
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}
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//-----------------------------------------------------------------------
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/**
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* Constructs a new empty <code>DefaultedMap</code> that decorates
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* a <code>HashMap</code>.
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* <p>
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* The object passed in will be returned by the map whenever an
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* unknown key is requested.
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*
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* @param defaultValue the default value to return when the key is not found
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*/
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public DefaultedMap(Object defaultValue) {
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super(new HashMap());
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if (defaultValue instanceof Transformer) {
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defaultValue = ConstantTransformer.getInstance(defaultValue);
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}
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this.value = defaultValue;
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}
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/**
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* Constructor that wraps (not copies).
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*
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* @param map the map to decorate, must not be null
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* @param value the value to use
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* @throws IllegalArgumentException if map or transformer is null
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*/
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protected DefaultedMap(Map map, Object value) {
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super(map);
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this.value = value;
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}
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//-----------------------------------------------------------------------
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/**
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* Write the map out using a custom routine.
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*
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* @param out the output stream
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* @throws IOException
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*/
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private void writeObject(ObjectOutputStream out) throws IOException {
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out.defaultWriteObject();
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out.writeObject(map);
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}
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/**
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* Read the map in using a custom routine.
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*
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* @param in the input stream
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* @throws IOException
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* @throws ClassNotFoundException
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*/
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private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
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in.defaultReadObject();
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map = (Map) in.readObject();
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}
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//-----------------------------------------------------------------------
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public Object get(Object key) {
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// create value for key if key is not currently in the map
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if (map.containsKey(key) == false) {
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if (value instanceof Transformer) {
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return ((Transformer) value).transform(key);
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}
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return value;
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}
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return map.get(key);
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}
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// no need to wrap keySet, entrySet or values as they are views of
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// existing map entries - you can't do a map-style get on them.
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}
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@ -1,5 +1,5 @@
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/*
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* Copyright 2003-2004 The Apache Software Foundation
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* Copyright 2003-2005 The Apache Software Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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@ -43,6 +43,7 @@ public class TestAll extends TestCase {
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suite.addTest(TestCaseInsensitiveMap.suite());
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suite.addTest(TestCompositeMap.suite());
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suite.addTest(TestDefaultedMap.suite());
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suite.addTest(TestFlat3Map.suite());
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suite.addTest(TestHashedMap.suite());
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suite.addTest(TestIdentityMap.suite());
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@ -0,0 +1,154 @@
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/*
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* Copyright 2005 The Apache Software Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.commons.collections.map;
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import java.util.HashMap;
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import java.util.Map;
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import junit.framework.Test;
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import junit.framework.TestSuite;
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import org.apache.commons.collections.Factory;
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import org.apache.commons.collections.FactoryUtils;
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import org.apache.commons.collections.Transformer;
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import org.apache.commons.collections.functors.ConstantFactory;
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/**
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* Extension of {@link TestMap} for exercising the
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* {@link DefaultedMap} implementation.
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*
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* @since Commons Collections 3.2
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* @version $Revision: 155406 $ $Date$
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*
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* @author Stephen Colebourne
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*/
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public class TestDefaultedMap extends AbstractTestMap {
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protected static final Factory nullFactory = FactoryUtils.nullFactory();
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public TestDefaultedMap(String testName) {
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super(testName);
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}
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public static Test suite() {
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return new TestSuite(TestDefaultedMap.class);
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}
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public static void main(String args[]) {
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String[] testCaseName = { TestDefaultedMap.class.getName()};
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junit.textui.TestRunner.main(testCaseName);
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}
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//-----------------------------------------------------------------------
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public Map makeEmptyMap() {
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return DefaultedMap.decorate(new HashMap(), nullFactory);
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}
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//-----------------------------------------------------------------------
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public void testMapGet() {
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Map map = new DefaultedMap("NULL");
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assertEquals(0, map.size());
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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map.put("Key", "Value");
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assertEquals(1, map.size());
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assertEquals(true, map.containsKey("Key"));
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assertEquals("Value", map.get("Key"));
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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}
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public void testMapGet2() {
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HashMap base = new HashMap();
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Map map = DefaultedMap.decorate(base, "NULL");
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assertEquals(0, map.size());
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assertEquals(0, base.size());
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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map.put("Key", "Value");
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assertEquals(1, map.size());
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assertEquals(1, base.size());
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assertEquals(true, map.containsKey("Key"));
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assertEquals("Value", map.get("Key"));
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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}
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public void testMapGet3() {
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HashMap base = new HashMap();
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Map map = DefaultedMap.decorate(base, ConstantFactory.getInstance("NULL"));
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assertEquals(0, map.size());
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assertEquals(0, base.size());
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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map.put("Key", "Value");
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assertEquals(1, map.size());
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assertEquals(1, base.size());
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assertEquals(true, map.containsKey("Key"));
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assertEquals("Value", map.get("Key"));
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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}
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public void testMapGet4() {
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HashMap base = new HashMap();
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Map map = DefaultedMap.decorate(base, new Transformer() {
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public Object transform(Object input) {
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if (input instanceof String) {
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return "NULL";
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}
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return "NULL_OBJECT";
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}
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});
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assertEquals(0, map.size());
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assertEquals(0, base.size());
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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assertEquals("NULL_OBJECT", map.get(new Integer(0)));
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map.put("Key", "Value");
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assertEquals(1, map.size());
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assertEquals(1, base.size());
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assertEquals(true, map.containsKey("Key"));
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assertEquals("Value", map.get("Key"));
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assertEquals(false, map.containsKey("NotInMap"));
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assertEquals("NULL", map.get("NotInMap"));
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assertEquals("NULL_OBJECT", map.get(new Integer(0)));
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}
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public String getCompatibilityVersion() {
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return "3.2";
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}
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// public void testCreate() throws Exception {
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// resetEmpty();
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// writeExternalFormToDisk(
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// (java.io.Serializable) map,
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// "c:/commons/collections/data/test/DefaultedMap.emptyCollection.version3.2.obj");
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// resetFull();
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// writeExternalFormToDisk(
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// (java.io.Serializable) map,
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// "c:/commons/collections/data/test/DefaultedMap.fullCollection.version3.2.obj");
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// }
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}
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