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/**
 * Copyright 2013-2022 Valery Silaev (http://vsilaev.com)
 *
 * 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 org.apache.commons.javaflow.spi;

import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.util.Map;
import java.util.WeakHashMap;

abstract public class Cache {
    private final Map> storage = new WeakHashMap>();
    
    synchronized public V get(K key) {
        Reference valueRef = storage.get(key);
        V value = null == valueRef ? null : valueRef.get();
        if (null == value) {
            value = createValue(key);
            storage.put(key, new SoftReference(value));
        }
        return value;
    }
    
    abstract protected V createValue(K key);
}