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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package com.sun.beans;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

import java.util.Map;
import java.util.WeakHashMap;

A hashtable-based cache with weak keys and weak values.
An entry in the map will be automatically removed
when its key is no longer in the ordinary use.
A value will be automatically removed as well
when it is no longer in the ordinary use.
Author:
Sergey A. Malenkov
Since:
1.7/**
 * A hashtable-based cache with weak keys and weak values.
 * An entry in the map will be automatically removed
 * when its key is no longer in the ordinary use.
 * A value will be automatically removed as well
 * when it is no longer in the ordinary use.
 *
 * @since 1.7
 *
 * @author Sergey A. Malenkov
 */
public final class WeakCache<K, V> {
    private final Map<K, Reference<V>> map = new WeakHashMap<K, Reference<V>>();

    
Returns a value to which the specified key is mapped, or null if this map contains no mapping for the key. 
Params:
key –  the key whose associated value is returned
Returns:
a value to which the specified key is mapped/**
     * Returns a value to which the specified {@code key} is mapped,
     * or {@code null} if this map contains no mapping for the {@code key}.
     *
     * @param key  the key whose associated value is returned
     * @return a value to which the specified {@code key} is mapped
     */
    public V get(K key) {
        Reference<V> reference = this.map.get(key);
        if (reference == null) {
            return null;
        }
        V value = reference.get();
        if (value == null) {
            this.map.remove(key);
        }
        return value;
    }

    
Associates the specified value with the specified key. Removes the mapping for the specified key from this cache if it is present and the specified value is null. If the cache previously contained a mapping for the key, the old value is replaced by the specified value. 
Params:
key –    the key with which the specified value is associated
value –  the value to be associated with the specified key/**
     * Associates the specified {@code value} with the specified {@code key}.
     * Removes the mapping for the specified {@code key} from this cache
     * if it is present and the specified {@code value} is {@code null}.
     * If the cache previously contained a mapping for the {@code key},
     * the old value is replaced by the specified {@code value}.
     *
     * @param key    the key with which the specified value is associated
     * @param value  the value to be associated with the specified key
     */
    public void put(K key, V value) {
        if (value != null) {
            this.map.put(key, new WeakReference<V>(value));
        }
        else {
            this.map.remove(key);
        }
    }

    
Removes all of the mappings from this cache.
/**
     * Removes all of the mappings from this cache.
     */
    public void clear() {
        this.map.clear();
    }
}