com.google.code.liquidform.internal.WeakIdentityHashMap Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of liquidform.jpa Show documentation

Provides a Java Domain Specific Language for building type-safe and refactoring proof JPA queries.

The newest version!

/*
 * Copyright (C) 2008-2009 the original author or authors
 * 
 * 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.google.code.liquidform.internal;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.WeakHashMap;

/**
 * Quick and dirty mix of {@link WeakHashMap} and {@link IdentityHashMap}. This
 * class does not implement {@link Map} per se but provides the methods
 * we need.
 */
/* default */class WeakIdentityHashMap {

	/**
	 * Considers that two objects are equal when they both reference the same
	 * (with == semantics) referent.
	 */
	private static class IdentityWeakReference extends WeakReference {
		private final int hashCode;

		IdentityWeakReference(T o) {
			this(o, null);
		}

		IdentityWeakReference(T o, ReferenceQueue q) {
			super(o, q);
			this.hashCode = (o == null) ? 0 : System.identityHashCode(o);
		}

		@Override
		public boolean equals(Object o) {
			if (this == o) {
				return true;
			}
			if (!(o instanceof IdentityWeakReference)) {
				return false;
			}
			IdentityWeakReference wr = (IdentityWeakReference) o;
			T got = get();
			return (got != null && got == wr.get());
		}

		@Override
		public int hashCode() {
			return hashCode;
		}
	}

	private Map, V> map = new HashMap, V>();

	private ReferenceQueue referenceQueue = new ReferenceQueue();

	private void expunge() {
		Reference ref;
		while ((ref = referenceQueue.poll()) != null) {
			map.remove(ref);
		}
	}

	public V get(K key) {
		expunge();
		WeakReference keyref = makeReference(key);
		return map.get(keyref);
	}

	private WeakReference makeReference(K referent) {
		return new IdentityWeakReference(referent);
	}

	private WeakReference makeReference(K referent, ReferenceQueue q) {
		return new IdentityWeakReference(referent, q);
	}

	public V put(K key, V value) {
		expunge();
		if (key == null) {
			throw new NullPointerException("Null key");
		}
		WeakReference keyref = makeReference(key, referenceQueue);
		return map.put(keyref, value);
	}

	public V remove(K key) {
		expunge();
		WeakReference keyref = makeReference(key);
		return map.remove(keyref);
	}
}