bundles/org.eclipse.ui.workbench/Eclipse UI/org/eclipse/ui/internal/ReferenceCounter.java

package org.eclipse.ui.internal;

/*
 * (c) Copyright IBM Corp. 2000, 2001.
 * All Rights Reserved.
 */
import java.util.*;

/**
 * A ReferenceCounter is used to reference counting objects.
 * Each object is identified by a unique ID.  Together they form
 * an ID - value pair. An object is added to the counter by calling
 * #put(id, object).  From this point on additional refs can be made
 * by calling #addRef(id) or #removeRef(id).
 */
public class ReferenceCounter
{
	private Map mapIdToRec = new HashMap(11);

	/**
	 * Capture the information about an object.
	 */
	public class RefRec {
		public RefRec(Object id, Object value) {
			this.id = id;
			this.value = value;
			addRef();
		}
		public Object getId() { 
			return id;
		}
		public Object getValue() { 
			return value;
		}
		public int addRef() { 
			++ refCount;
			return refCount;
		}
		public int removeRef() { 
			-- refCount;
			return refCount;
		}
		public int getRef() {
			return refCount;
		}
		public boolean isNotReferenced() { 
			return (refCount <= 0); 
		}
		public Object id;
		public Object value;
		private int refCount; 
	}
/**
 * Creates a new counter.
 */
public ReferenceCounter() {
	super();
}
/**
 * Adds one reference to an object in the counter.
 *
 * @param id is a unique ID for the object.
 * @return the new ref count
 */
public int addRef(Object id) {
	RefRec rec = (RefRec)mapIdToRec.get(id);
	if (rec == null)
		return 0;
	return rec.addRef();
}
/**
 * Returns the object defined by an ID.  If the ID is not
 * found <code>null</code> is returned.
 *
 * @return the object or <code>null</code>
 */
public Object get(Object id) {
	RefRec rec = (RefRec)mapIdToRec.get(id);
	if (rec == null)
		return null;
	return rec.getValue();
}
/**
 * Returns a complete list of the keys in the counter.
 *
 * @return a Set containing the ID for each.
 */
public Set keySet() {
	return mapIdToRec.keySet();
}
/**
 * Adds an object to the counter for counting and gives
 * it an initial ref count of 1.
 *
 * @param id is a unique ID for the object.
 * @param value is the object itself.
 */
public void put(Object id, Object value) {
	RefRec rec = new RefRec(id, value);
	mapIdToRec.put(id, rec);
}
/**
 * Removes one reference from an object in the counter.
 * If the ref count drops to 0 the object is removed from
 * the counter completely.
 *
 * @param id is a unique ID for the object.
 * @return the new ref count
 */
public int removeRef(Object id) {
	RefRec rec = (RefRec)mapIdToRec.get(id);
	if (rec == null)
		return 0;
	int newCount = rec.removeRef();
	if (newCount <= 0)
		mapIdToRec.remove(id);
	return newCount;
}
/**
 * Returns a complete list of the values in the counter.
 *
 * @return a Collection containing the values.
 */
public List values() {
	int size = mapIdToRec.size();
	ArrayList list = new ArrayList(size);
	Iterator iter = mapIdToRec.values().iterator();
	while (iter.hasNext()) {
		RefRec rec = (RefRec)iter.next();
		list.add(rec.getValue());
	}
	return list;
}
}