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Commons Collections example source code file (DefaultKeyValue.java)

This example Commons Collections source code file (DefaultKeyValue.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

abstractkeyvalue, defaultkeyvalue, defaultkeyvalue, defaultmapentry, defaultmapentry, illegalargumentexception, illegalargumentexception, keyvalue, object, object, util

The Commons Collections DefaultKeyValue.java source code

/*
 *  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.collections.keyvalue;

import java.util.Map;

import org.apache.commons.collections.KeyValue;

/**
 * A mutable <code>KeyValue pair that does not implement
 * {@link java.util.Map.Entry Map.Entry}.
 * <p>
 * Note that a <code>DefaultKeyValue instance may not contain
 * itself as a key or value.
 *
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 * 
 * @author James Strachan
 * @author Michael A. Smith
 * @author Neil O'Toole
 * @author Stephen Colebourne
 */
public class DefaultKeyValue extends AbstractKeyValue {

    /**
     * Constructs a new pair with a null key and null value.
     */
    public DefaultKeyValue() {
        super(null, null);
    }

    /**
     * Constructs a new pair with the specified key and given value.
     *
     * @param key  the key for the entry, may be null
     * @param value  the value for the entry, may be null
     */
    public DefaultKeyValue(final Object key, final Object value) {
        super(key, value);
    }

    /**
     * Constructs a new pair from the specified <code>KeyValue.
     *
     * @param pair  the pair to copy, must not be null
     * @throws NullPointerException if the entry is null
     */
    public DefaultKeyValue(final KeyValue pair) {
        super(pair.getKey(), pair.getValue());
    }

    /**
     * Constructs a new pair from the specified <code>Map.Entry.
     *
     * @param entry  the entry to copy, must not be null
     * @throws NullPointerException if the entry is null
     */
    public DefaultKeyValue(final Map.Entry entry) {
        super(entry.getKey(), entry.getValue());
    }

    //-----------------------------------------------------------------------
    /**
     * Sets the key.
     *
     * @param key  the new key
     * @return the old key
     * @throws IllegalArgumentException if key is this object
     */
    public Object setKey(final Object key) {
        if (key == this) {
            throw new IllegalArgumentException("DefaultKeyValue may not contain itself as a key.");
        }

        final Object old = this.key;
        this.key = key;
        return old;
    }

    /** 
     * Sets the value.
     *
     * @return the old value of the value
     * @param value the new value
     * @throws IllegalArgumentException if value is this object
     */
    public Object setValue(final Object value) {
        if (value == this) {
            throw new IllegalArgumentException("DefaultKeyValue may not contain itself as a value.");
        }

        final Object old = this.value;
        this.value = value;
        return old;
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a new <code>Map.Entry object with key and value from this pair.
     * 
     * @return a MapEntry instance
     */
    public Map.Entry toMapEntry() {
        return new DefaultMapEntry(this);
    }

    //-----------------------------------------------------------------------
    /**
     * Compares this <code>Map.Entry with another Map.Entry.
     * <p>
     * Returns true if the compared object is also a <code>DefaultKeyValue,
     * and its key and value are equal to this object's key and value.
     * 
     * @param obj  the object to compare to
     * @return true if equal key and value
     */
    public boolean equals(final Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof DefaultKeyValue == false) {
            return false;
        }

        DefaultKeyValue other = (DefaultKeyValue) obj;
        return 
            (getKey() == null ? other.getKey() == null : getKey().equals(other.getKey())) &&
            (getValue() == null ? other.getValue() == null : getValue().equals(other.getValue()));
    }

    /**
     * Gets a hashCode compatible with the equals method.
     * <p>
     * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()},
     * however subclasses may override this.
     * 
     * @return a suitable hash code
     */
    public int hashCode() {
        return (getKey() == null ? 0 : getKey().hashCode()) ^
               (getValue() == null ? 0 : getValue().hashCode());
    }

}

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