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/**
 * Copyright (C) 2010 Mycila ([email protected])
 *
 * Licensed 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 com.mycila.event.internal;

import java.lang.ref.WeakReference;
import java.util.WeakHashMap;

/**
 * @author Mathieu Carbou ([email protected])
 */
final class WeakCache {

    private static final Object NULL = new Object();

    private final WeakHashMap> cache = new WeakHashMap>();
    private final Provider provider;

    public WeakCache(Provider provider) {
        this.provider = provider;
    }

    public V get(K key) {
        WeakReference ref = cache.get(key);
        V val = null;
        if (ref != null)
            val = ref.get();
        if (val == null) {
            val = provider.get(key);
            if (val == null)
                val = (V) NULL;
            cache.put(key, new WeakReference(val));
        }
        return val == NULL ? null : val;
    }

    public static interface Provider {
        V get(K key);
    }

}