UnwrappedWeakReference.java

package com.cloudhopper.commons.util;

/*
 * #%L
 * ch-commons-util
 * %%
 * Copyright (C) 2012 Cloudhopper by Twitter
 * %%
 * 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.
 * #L%
 */

import java.lang.ref.WeakReference;

/**
 * Smarter WeakReference that "unwraps" the referenced object in a few methods
 * such as "equals()" which let a WeakReference be used in many other types of
 * collections and lists and have them still work correctly. For exmaple, 
 * CopyOnWriteArrayList can be directly used with a UnwrappedWeakReference and
 * have methods like "addIfAbsent" actually work correctly.
 * 
 * @author joelauer (twitter: @jjlauer or <a href="http://twitter.com/jjlauer" target=window>http://twitter.com/jjlauer</a>)
 */
public class UnwrappedWeakReference<T> extends WeakReference<T> {
    
    public UnwrappedWeakReference(T ref) {
        super(ref);
    }

    @Override
    public boolean equals(Object obj) {
        // unwrap both objects!
        T thisObject = this.get();
        
        // if the other object is also a WeakRefe
        if (obj instanceof WeakReference) {
            obj = ((WeakReference)obj).get();
        }
        
        // check if anything is null (was garbage collected)
        if (thisObject == null) {
            if (obj == null) {
                return true;
            } else {
                return false;
            }
        }
        
        return thisObject.equals(obj);
    }

    @Override
    public int hashCode() {
        // unwrap me!
        T thisObject = this.get();
        
        // check if anything is null (was garbage collected)
        if (thisObject == null) {
            return 0;
        } else {
            return thisObject.hashCode();
        }
    }
    
}