ObjectCache.java

/*******************************************************************************
 * Copyright (c) 2000, 2009 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.compiler.codegen;

public class ObjectCache {
	public Object keyTable[];
	public int valueTable[];
	int elementSize;
	int threshold;
/**
 * Constructs a new, empty hashtable. A default capacity is used.
 * Note that the hashtable will automatically grow when it gets full.
 */
public ObjectCache() {
	this(13);
}
/**
 * Constructs a new, empty hashtable with the specified initial
 * capacity.
 * @param initialCapacity int
 *  the initial number of buckets
 */
public ObjectCache(int initialCapacity) {
	this.elementSize = 0;
	this.threshold = (int) (initialCapacity * 0.66f);
	this.keyTable = new Object[initialCapacity];
	this.valueTable = new int[initialCapacity];
}
/**
 * Clears the hash table so that it has no more elements in it.
 */
public void clear() {
	for (int i = this.keyTable.length; --i >= 0;) {
		this.keyTable[i] = null;
		this.valueTable[i] = 0;
	}
	this.elementSize = 0;
}
/** Returns true if the collection contains an element for the key.
 *
 * @param key char[] the key that we are looking for
 * @return boolean
 */
public boolean containsKey(Object key) {
	int index = hashCode(key), length = this.keyTable.length;
	while (this.keyTable[index] != null) {
		if (this.keyTable[index] == key)
			return true;
		if (++index == length) {
			index = 0;
		}
	}
	return false;
}
/** Gets the object associated with the specified key in the
 * hashtable.
 * @param key <CODE>char[]</CODE> the specified key
 * @return int the element for the key or -1 if the key is not
 *  defined in the hash table.
 */
public int get(Object key) {
	int index = hashCode(key), length = this.keyTable.length;
	while (this.keyTable[index] != null) {
		if (this.keyTable[index] == key)
			return this.valueTable[index];
		if (++index == length) {
			index = 0;
		}
	}
	return -1;
}
/**
 * Return the hashcode for the key parameter
 *
 * @param key org.eclipse.jdt.internal.compiler.lookup.MethodBinding
 * @return int
 */
public int hashCode(Object key) {
	return (key.hashCode() & 0x7FFFFFFF) % this.keyTable.length;
}
/**
 * Puts the specified element into the hashtable, using the specified
 * key.  The element may be retrieved by doing a get() with the same key.
 * The key and the element cannot be null.
 *
 * @param key <CODE>Object</CODE> the specified key in the hashtable
 * @param value <CODE>int</CODE> the specified element
 * @return int the old value of the key, or -1 if it did not have one.
 */
public int put(Object key, int value) {
	int index = hashCode(key), length = this.keyTable.length;
	while (this.keyTable[index] != null) {
		if (this.keyTable[index] == key)
			return this.valueTable[index] = value;
		if (++index == length) {
			index = 0;
		}
	}
	this.keyTable[index] = key;
	this.valueTable[index] = value;

	// assumes the threshold is never equal to the size of the table
	if (++this.elementSize > this.threshold)
		rehash();
	return value;
}
/**
 * Rehashes the content of the table into a bigger table.
 * This method is called automatically when the hashtable's
 * size exceeds the threshold.
 */
private void rehash() {
	ObjectCache newHashtable = new ObjectCache(this.keyTable.length * 2);
	for (int i = this.keyTable.length; --i >= 0;)
		if (this.keyTable[i] != null)
			newHashtable.put(this.keyTable[i], this.valueTable[i]);

	this.keyTable = newHashtable.keyTable;
	this.valueTable = newHashtable.valueTable;
	this.threshold = newHashtable.threshold;
}
/**
 * Returns the number of elements contained in the hashtable.
 *
 * @return <CODE>int</CODE> The size of the table
 */
public int size() {
	return this.elementSize;
}
/**
 * Converts to a rather lengthy String.
 *
 * @return String the ascii representation of the receiver
 */
public String toString() {
	int max = size();
	StringBuffer buf = new StringBuffer();
	buf.append("{"); //$NON-NLS-1$
	for (int i = 0; i < max; ++i) {
		if (this.keyTable[i] != null) {
			buf.append(this.keyTable[i]).append("->").append(this.valueTable[i]); //$NON-NLS-1$
		}
		if (i < max) {
			buf.append(", "); //$NON-NLS-1$
		}
	}
	buf.append("}"); //$NON-NLS-1$
	return buf.toString();
}
}