SimpleLookupTable.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.util;

/**
 * A simple lookup table is a non-synchronized Hashtable, whose keys and values are Objects. It also
 * uses linear probing to resolve collisions rather than a linked list of hash table entries.
 */
public final class SimpleLookupTable implements Cloneable {

// to avoid using Enumerations, walk the individual tables skipping nulls
	public Object[] keyTable;

	public Object[] valueTable;

	public int elementSize; // number of elements in the table

	public int threshold;

	public SimpleLookupTable() {
		this(13);
	}

	public SimpleLookupTable(int size) {
		this.elementSize= 0;
		this.threshold= size; // size represents the expected number of elements
		int extraRoom= (int)(size * 1.5f);
		if (this.threshold == extraRoom)
			extraRoom++;
		this.keyTable= new Object[extraRoom];
		this.valueTable= new Object[extraRoom];
	}

	public Object clone() throws CloneNotSupportedException {
		SimpleLookupTable result= (SimpleLookupTable)super.clone();
		result.elementSize= this.elementSize;
		result.threshold= this.threshold;

		int length= this.keyTable.length;
		result.keyTable= new Object[length];
		System.arraycopy(this.keyTable, 0, result.keyTable, 0, length);

		length= this.valueTable.length;
		result.valueTable= new Object[length];
		System.arraycopy(this.valueTable, 0, result.valueTable, 0, length);
		return result;
	}

	public boolean containsKey(Object key) {
		int length= this.keyTable.length;
		int index= (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey= this.keyTable[index]) != null) {
			if (currentKey.equals(key))
				return true;
			if (++index == length)
				index= 0;
		}
		return false;
	}

	public Object get(Object key) {
		int length= this.keyTable.length;
		int index= (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey= this.keyTable[index]) != null) {
			if (currentKey.equals(key))
				return this.valueTable[index];
			if (++index == length)
				index= 0;
		}
		return null;
	}

	public Object getKey(Object key) {
		int length= this.keyTable.length;
		int index= (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey= this.keyTable[index]) != null) {
			if (currentKey.equals(key))
				return currentKey;
			if (++index == length)
				index= 0;
		}
		return key;
	}

	public Object keyForValue(Object valueToMatch) {
		if (valueToMatch != null)
			for (int i= 0, l= this.keyTable.length; i < l; i++)
				if (this.keyTable[i] != null && valueToMatch.equals(this.valueTable[i]))
					return this.keyTable[i];
		return null;
	}

	public Object put(Object key, Object value) {
		int length= this.keyTable.length;
		int index= (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey= this.keyTable[index]) != null) {
			if (currentKey.equals(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;
	}

	public Object removeKey(Object key) {
		int length= this.keyTable.length;
		int index= (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey= this.keyTable[index]) != null) {
			if (currentKey.equals(key)) {
				this.elementSize--;
				Object oldValue= this.valueTable[index];
				this.keyTable[index]= null;
				this.valueTable[index]= null;
				if (this.keyTable[index + 1 == length ? 0 : index + 1] != null)
					rehash(); // only needed if a possible collision existed
				return oldValue;
			}
			if (++index == length)
				index= 0;
		}
		return null;
	}

	public void removeValue(Object valueToRemove) {
		boolean rehash= false;
		for (int i= 0, l= this.valueTable.length; i < l; i++) {
			Object value= this.valueTable[i];
			if (value != null && value.equals(valueToRemove)) {
				this.elementSize--;
				this.keyTable[i]= null;
				this.valueTable[i]= null;
				if (!rehash && this.keyTable[i + 1 == l ? 0 : i + 1] != null)
					rehash= true; // only needed if a possible collision existed
			}
		}
		if (rehash)
			rehash();
	}

	private void rehash() {
		SimpleLookupTable newLookupTable= new SimpleLookupTable(this.elementSize * 2); // double the number of expected elements
		Object currentKey;
		for (int i= this.keyTable.length; --i >= 0;)
			if ((currentKey= this.keyTable[i]) != null)
				newLookupTable.put(currentKey, this.valueTable[i]);

		this.keyTable= newLookupTable.keyTable;
		this.valueTable= newLookupTable.valueTable;
		this.elementSize= newLookupTable.elementSize;
		this.threshold= newLookupTable.threshold;
	}

	public String toString() {
		String s= ""; //$NON-NLS-1$
		Object object;
		for (int i= 0, l= this.valueTable.length; i < l; i++)
			if ((object= this.valueTable[i]) != null)
				s+= this.keyTable[i].toString() + " -> " + object.toString() + "\n"; //$NON-NLS-2$ //$NON-NLS-1$
		return s;
	}
}