IntegerCache.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 IntegerCache {
	public int keyTable[];

	public int valueTable[];

	int elementSize;

	int threshold;

	/**
	 * Constructs a new, empty hashtable. A default capacity and load factor is used. Note that the
	 * hashtable will automatically grow when it gets full.
	 */
	public IntegerCache() {
		this(13);
	}

	/**
	 * Constructs a new, empty hashtable with the specified initial capacity.
	 * 
	 * @param initialCapacity int the initial number of buckets
	 */
	public IntegerCache(int initialCapacity) {
		this.elementSize= 0;
		this.threshold= (int)(initialCapacity * 0.66);
		this.keyTable= new int[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]= 0;
			this.valueTable[i]= 0;
		}
		this.elementSize= 0;
	}

	/**
	 * Returns true if the collection contains an element for the key.
	 * 
	 * @param key <CODE>double</CODE> the key that we are looking for
	 * @return boolean
	 */
	public boolean containsKey(int key) {
		int index= hash(key), length= this.keyTable.length;
		while ((this.keyTable[index] != 0) || ((this.keyTable[index] == 0) && (this.valueTable[index] != 0))) {
			if (this.keyTable[index] == key)
				return true;
			if (++index == length) {
				index= 0;
			}
		}
		return false;
	}

	/**
	 * Return a hashcode for the value of the key parameter.
	 * 
	 * @param key int
	 * @return int the hash code corresponding to the key value
	 */
	public int hash(int key) {
		return (key & 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.
	 * 
	 * @param key <CODE>int</CODE> the specified key in the hashtable
	 * @param value <CODE>int</CODE> the specified element
	 * @return int value
	 */
	public int put(int key, int value) {
		int index= hash(key), length= this.keyTable.length;
		while ((this.keyTable[index] != 0) || ((this.keyTable[index] == 0) && (this.valueTable[index] != 0))) {
			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;
	}

	/**
	 * Puts the specified element into the hashtable if absent, using the specified key. The element
	 * may be retrieved by doing a get() with the same key.
	 * 
	 * @param key <CODE>int</CODE> the specified key in the hashtable
	 * @param value <CODE>int</CODE> the specified element
	 * @return int value
	 */
	public int putIfAbsent(int key, int value) {
		int index= hash(key), length= this.keyTable.length;
		while ((this.keyTable[index] != 0) || ((this.keyTable[index] == 0) && (this.valueTable[index] != 0))) {
			if (this.keyTable[index] == key)
				return this.valueTable[index];
			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; // negative when added, assumes value is > 0
	}

	/**
	 * 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() {
		IntegerCache newHashtable= new IntegerCache(this.keyTable.length * 2);
		for (int i= this.keyTable.length; --i >= 0;) {
			int key= this.keyTable[i];
			int value= this.valueTable[i];
			if ((key != 0) || ((key == 0) && (value != 0))) {
				newHashtable.put(key, value);
			}
		}
		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] != 0) || ((this.keyTable[i] == 0) && (this.valueTable[i] != 0))) {
				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();
	}
}