/******************************************************************************* * Copyright (c) 2005 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.core.commands;import java.util.HashMap;import java.util.Map;import java.util.Set;/** * <p> * An abstract implementation of {@link IObjectWithState}. This provides basic * handling for adding and remove state. When state is added, the handler * attaches itself as a listener and fire a handleStateChange event to notify * this handler. When state is removed, the handler removes itself as a * listener. * </p> * <p> * Clients may extend this class. * </p> * <p> * <strong>EXPERIMENTAL</strong>. This class or interface has been added as * part of a work in progress. There is a guarantee neither that this API will * work nor that it will remain the same. Please do not use this API without * consulting with the Platform/UI team. * </p> *  * @since 3.2 */public abstract class AbstractHandlerWithState extends AbstractHandler		implements IObjectWithState, IStateListener {	/**	 * The map of states currently held by this handler. If this handler has no	 * state (generally, when inactive), then this will be <code>null</code>.	 */	private Map states = null;	/**	 * <p>	 * Adds a state to this handler. This will add this handler as a listener to	 * the state, and then fire a handleStateChange so that the handler can	 * respond to the incoming state.	 * </p>	 * <p>	 * Clients may extend this method, but they should call this super method	 * first before doing anything else.	 * </p>	 * 	 * @param id	 *            The identifier indicating the type of state being added; must	 *            not be <code>null</code>.	 * @param state	 *            The state to add; must not be <code>null</code>.	 */	public void addState(final String stateId, final IState state) {		if (state == null) {			throw new NullPointerException("Cannot add a null state"); //$NON-NLS-1$		}		if (states == null) {			states = new HashMap(3);		}		states.put(stateId, state);		state.addListener(this);		handleStateChange(state, null);	}	public final IState getState(final String stateId) {		if ((states == null) || (states.isEmpty())) {			return null;		}		return (IState) states.get(stateId);	}	public final String[] getStateIds() {		if ((states == null) || (states.isEmpty())) {			return null;		}		final Set stateIds = states.keySet();		return (String[]) stateIds.toArray(new String[stateIds.size()]);	}	/**	 * <p>	 * Removes a state from this handler. This will remove this handler as a	 * listener to the state. No event is fired to notify the handler of this	 * change.	 * </p>	 * <p>	 * Clients may extend this method, but they should call this super method	 * first before doing anything else.	 * </p>	 * 	 * @param stateId	 *            The identifier of the state to remove; must not be	 *            <code>null</code>.	 */	public void removeState(final String stateId) {		if (stateId == null) {			throw new NullPointerException("Cannot remove a null state"); //$NON-NLS-1$		}		final IState state = (IState) states.get(stateId);		if (state != null) {			state.removeListener(this);			if (states != null) {				states.remove(state);				if (states.isEmpty()) {					states = null;				}			}		}	}}