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/**
 * 
 */
package clime.messadmin.utils;

import java.io.Serializable;
import java.util.Map;

/**
 * An Entry maintaining a key and a value.  The value may be
 * changed using the setValue method.  This class
 * facilitates the process of building custom map
 * implementations. For example, it may be convenient to return
 * arrays of SimpleEntry instances in method
 * Map.entrySet().toArray.
 *
 * @since 1.6
 * @author Cédrik LIME
 */
public class SimpleEntry implements Map.Entry, Serializable {
	private final Object key;
	private Object value;

	/**
	 * Creates an entry representing a mapping from the specified
	 * key to the specified value.
	 *
	 * @param key the key represented by this entry
	 * @param value the value represented by this entry
	 */
	public SimpleEntry(Object key, Object value) {
		this.key   = key;
		this.value = value;
	}

	/**
	 * Creates an entry representing the same mapping as the
	 * specified entry.
	 *
	 * @param entry the entry to copy
	 */
	public SimpleEntry(Map.Entry entry) {
		this.key   = entry.getKey();
		this.value = entry.getValue();
	}

	/**
	 * @return the key corresponding to this entry
	 */
	public Object getKey() {
		return key;
	}

	/**
	 * @return the value corresponding to this entry
	 */
	public Object getValue() {
		return value;
	}

	/**
	 * Replaces the value corresponding to this entry with the specified
	 * value.
	 *
	 * @param value new value to be stored in this entry
	 * @return the old value corresponding to the entry
	 */
	public Object setValue(Object value) {
		Object oldValue = this.value;
		this.value = value;
		return oldValue;
	}

	/**
	 * Compares the specified object with this entry for equality.
	 * Returns {@code true} if the given object is also a map entry and
	 * the two entries represent the same mapping.	More formally, two
	 * entries {@code e1} and {@code e2} represent the same mapping
	 * if	 *   (e1.getKey()==null ?
	 *	  e2.getKey()==null :
	 *	  e1.getKey().equals(e2.getKey()))
	 *   &&
	 *   (e1.getValue()==null ?
	 *	  e2.getValue()==null :
	 *	  e1.getValue().equals(e2.getValue()))
	 * This ensures that the {@code equals} method works properly across
	 * different implementations of the {@code Map.Entry} interface.
	 *
	 * @param o object to be compared for equality with this map entry
	 * @return {@code true} if the specified object is equal to this map
	 *	   entry
	 * @see	#hashCode
	 */
	public boolean equals(Object o) {
		if (!(o instanceof Map.Entry))
			return false;
		Map.Entry e = (Map.Entry)o;
		return eq(key, e.getKey()) && eq(value, e.getValue());
	}

	/**
	 * Returns the hash code value for this map entry.  The hash code
	 * of a map entry {@code e} is defined to be: 	 *   (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
	 *   (e.getValue()==null ? 0 : e.getValue().hashCode())
	 * This ensures that {@code e1.equals(e2)} implies that
	 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
	 * {@code e1} and {@code e2}, as required by the general
	 * contract of {@link Object#hashCode}.
	 *
	 * @return the hash code value for this map entry
	 * @see	#equals
	 */
	public int hashCode() {
		return (key   == null ? 0 :   key.hashCode()) ^
		   (value == null ? 0 : value.hashCode());
	}

	/**
	 * Returns a String representation of this map entry.  This
	 * implementation returns the string representation of this
	 * entry's key followed by the equals character ("=")
	 * followed by the string representation of this entry's value.
	 *
	 * @return a String representation of this map entry
	 */
	public String toString() {
		return key + "=" + value;//$NON-NLS-1$
	}

	/**
	 * Utility method for SimpleEntry and SimpleImmutableEntry.
	 * Test for equality, checking for nulls.
	 */
	private static boolean eq(Object o1, Object o2) {
		return o1 == null ? o2 == null : o1.equals(o2);
	}
}