org.apache.jackrabbit.spi.commons.name.HashCache Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.jackrabbit.spi.commons.name;
/**
* Simple utility class that implements a fixed-size and thread-safe
* (non-blocking) cache of objects. The cache is simply an array
* of objects, indexed by their hash codes. If more than one objects
* hash to the same location, only the most recently accessed object is
* kept in the cache.
*
* @see JCR-1663
*/
public class HashCache {
/**
* Array of cached objects, indexed by their hash codes
* (module size of the array).
*/
private final T[] array;
/**
* Creates a hash cache with 1024 slots.
*/
public HashCache() {
this(10);
}
/**
* Creates a hash cache with 2^exponent slots.
*
* @param exponent the exponent.
*/
@SuppressWarnings("unchecked")
public HashCache(int exponent) {
this.array = (T[]) new Object[2 << exponent];
}
/**
* If a cached copy of the given object already exists, then returns
* that copy. Otherwise the given object is cached and returned.
*
* @param object object to return from the cache
* @return the given object or a previously cached copy
*/
public T get(T object) {
int position = object.hashCode() & (array.length - 1);
T previous = array[position];
if (object.equals(previous)) {
return previous;
} else {
array[position] = object;
return object;
}
}
}