/*******************************************************************************
 * Copyright (c) 2000, 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.ltk.core.refactoring;

/**
 * A content stamp object represent the content of an <code>IFile</code>.
 * A content stamp object is updated whenever the content of a file
 * changes. In contrast to a time stamp a content stamp is reverted
 * to its previous value if the content of the file is reverted back by
 * performing a corresponding undo change.
 * <p>
 * Clients of the refactoring framework don't need to take care of content
 * stamps. They are managed by the framework itself.
 * </p>
 * <p>
 * In version 3.0 not all files in the workspace are annotated with a content stamp. The 
 * refactoring framework only adds content stamp to those files where necessary. As of
 * version 3.1 the content stamps are mapped to the resource's modification stamp.
 * </p>
 * <p>
 * Content stamp are to be compared using the <code>equals(Object)</code> method.
 * It is not guaranteed that content stamps are identical for identical files.
 * </p>
 * <p>
 * This class is not intended to be extended by clients.
 * </p>
 * 
 * @since 3.0
 */
public abstract class ContentStamp {

	/**
	 * Checks whether the stamp is the null stamp or not. A null stamp
	 * is generated for files which either don't exist or exist in a 
	 * closed project.
	 * 
	 * @return whether the stamp is the null stamp or not.
	 */
	public abstract boolean isNullStamp();
}