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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package javax.swing.undo;

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

StateEdit is a general edit for objects that change state.
Objects being edited must conform to the StateEditable interface.
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.
A state edit is used as follows:
     // 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();

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!
Author:
Ray Ryan
See Also:
StateEditable/**
 * <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
 *
 * @author Ray Ryan
 */

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

    
The state information prior to the edit
/**
     * The state information prior to the edit
     */
    protected Hashtable<Object,Object> preState;

    
The state information after the edit
/**
     * The state information after the edit
     */
    protected Hashtable<Object,Object> postState;

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

    //
    // Constructors
    //

    
Create and return a new StateEdit.
Params:
anObject – The object to watch for changing state
See Also:
StateEdit/**
     * 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.
Params:
anObject – The object to watch for changing state
name – The presentation name to be used for this edit
See Also:
StateEdit/**
     * 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<Object, Object>(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.
/**
     * Gets the post-edit state of the StateEditable object and
     * ends the edit.
     */
    public void end() {
        this.postState = new Hashtable<Object, Object>(11);
        this.object.storeState(this.postState);
        this.removeRedundantState();
    }

    
Tells the edited object to apply the state prior to the edit
/**
     * 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
/**
     * 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
/**
     * Gets the presentation name for this edit
     */
    public String getPresentationName() {
        return this.undoRedoName;
    }


    //
    // Internal support
    //

    
Remove redundant key/values in state hashtables.
/**
     * Remove redundant key/values in state hashtables.
     */
    protected void removeRedundantState() {
        Vector<Object> uselessKeys = new Vector<Object>();
        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