SimpleSet.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 SimpleSet implements Cloneable {

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

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

	public int threshold;

	public SimpleSet() {
		this(13);
	}

	public SimpleSet(int size) {
		if (size < 3)
			size= 3;
		this.elementSize= 0;
		this.threshold= size + 1; // size is the expected number of elements
		this.values= new Object[2 * size + 1];
	}

	public Object add(Object object) {
		int length= this.values.length;
		int index= (object.hashCode() & 0x7FFFFFFF) % length;
		Object current;
		while ((current= this.values[index]) != null) {
			if (current.equals(object))
				return this.values[index]= object;
			if (++index == length)
				index= 0;
		}
		this.values[index]= object;

		// assumes the threshold is never equal to the size of the table
		if (++this.elementSize > this.threshold)
			rehash();
		return object;
	}

	public Object addIfNotIncluded(Object object) {
		int length= this.values.length;
		int index= (object.hashCode() & 0x7FFFFFFF) % length;
		Object current;
		while ((current= this.values[index]) != null) {
			if (current.equals(object))
				return null; // already existed
			if (++index == length)
				index= 0;
		}
		this.values[index]= object;

		// assumes the threshold is never equal to the size of the table
		if (++this.elementSize > this.threshold)
			rehash();
		return object;
	}

	public void asArray(Object[] copy) {
		if (this.elementSize != copy.length)
			throw new IllegalArgumentException();
		int index= this.elementSize;
		for (int i= 0, l= this.values.length; i < l && index > 0; i++)
			if (this.values[i] != null)
				copy[--index]= this.values[i];
	}

	public void clear() {
		for (int i= this.values.length; --i >= 0;)
			this.values[i]= null;
		this.elementSize= 0;
	}

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

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

	public boolean includes(Object object) {
		int length= this.values.length;
		int index= (object.hashCode() & 0x7FFFFFFF) % length;
		Object current;
		while ((current= this.values[index]) != null) {
			if (current.equals(object))
				return true;
			if (++index == length)
				index= 0;
		}
		return false;
	}

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

	private void rehash() {
		SimpleSet newSet= new SimpleSet(this.elementSize * 2); // double the number of expected elements
		Object current;
		for (int i= this.values.length; --i >= 0;)
			if ((current= this.values[i]) != null)
				newSet.add(current);

		this.values= newSet.values;
		this.elementSize= newSet.elementSize;
		this.threshold= newSet.threshold;
	}

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