Programming Languages Suite/ProgLangD.iso/VCAFE.3.0A/JFC.bin/StateEdit.java

Text File | 1998-06-30 | 5KB | 188 lines

/*
 * @(#)StateEdit.java       1.8 97/07/28
 *
 * Copyright (c) 1997 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 *
 */

package com.sun.java.swing.undo;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;


/**
* <P>StateEdit is a general edit for objects that change state.
* Objects being edited must conform to the StateEditable interface.</P>
*
* <P>This edit class works by asking an object to store it's state in
* Hashtables before and after editing occurs.  Upon undo or redo the
* object is told to restore it's state from these Hashtables.</P>
*
* A state edit is used as follows:
* <PRE>
*    // Create the edit during the "before" state of the object
*    StateEdit newEdit = new StateEdit(myObject);
*    // Modify the object
*    myObject.someStateModifyingMethod();
*    // "end" the edit when you are done modifying the object
*    newEdit.end();
* </PRE>
*
* <P><EM>Note that when a StateEdit ends, it removes redundant state from
* the Hashtables - A state Hashtable is not guaranteed to contain all
* keys/values placed into it when the state is stored!</EM></P>
*
* @see StateEditable
*/

public class StateEdit
    extends AbstractUndoableEdit {

    protected static final String RCSID = "$Id: StateEdit.java,v 1.6 1997/10/01 20:05:51 sandipc Exp $";

    //
    // Attributes
    //

    /**
     * The object being edited
     */
    protected StateEditable object;

    /**
     * The state information prior to the edit
     */
    protected Hashtable preState;

    /**
     * The state information after the edit
     */
    protected Hashtable postState;

    /**
     * The undo/redo presentation name
     */
    protected String undoRedoName;

    //
    // Constructors
    //

    /**
     * Create and return a new StateEdit.
     *
     * @param anObject The object to watch for changing state
     *
     * @see StateEdit
     */
    public StateEdit(StateEditable anObject) {
        super();
    init (anObject,null);
    }

    /**
     * Create and return a new StateEdit with a presentation name.
     *
     * @param anObject The object to watch for changing state
     * @param name The presentation name to be used for this edit
     *
     * @see StateEdit
     */
    public StateEdit(StateEditable anObject, String name) {
    super();
    init (anObject,name);
    }

    protected void init (StateEditable anObject, String name) {
    this.object = anObject;
    this.preState = new Hashtable(11);
    this.object.storeState(this.preState);
    this.postState = null;
    this.undoRedoName = name;
    }


    //
    // Operation
    //


    /**
     * Gets the post-edit state of the StateEditable object and
     * ends the edit.
     */
    public void end() {
    this.postState = new Hashtable(11);
    this.object.storeState(this.postState);
    this.removeRedundantState();
    }

    /**
     * Tells the edited object to apply the state prior to the edit
     */
    public void undo() {
    super.undo();
    this.object.restoreState(preState);
    }

    /**
     * Tells the edited object to apply the state after the edit
     */
    public void redo() {
    super.redo();
    this.object.restoreState(postState);
    }

    /**
     * Gets the presentation name for this edit
     */
    public String getPresentationName() {
    return this.undoRedoName;
    }


    //
    // Internal support
    //

    /**
     * Remove redundant key/values in state hashtables.
     */
    protected void removeRedundantState() {
    Vector uselessKeys = new Vector();
    Enumeration myKeys = preState.keys();

    // Locate redundant state
    while (myKeys.hasMoreElements()) {
        Object myKey = myKeys.nextElement();
        if (postState.containsKey(myKey) &&
        postState.get(myKey).equals(preState.get(myKey))) {
        uselessKeys.addElement(myKey);
        }
    }

    // Remove redundant state
    for (int i = uselessKeys.size()-1; i >= 0; i--) {
        Object myKey = uselessKeys.elementAt(i);
        preState.remove(myKey);
        postState.remove(myKey);
    }
    }

} // End of class StateEdit