bprocessor-commit

[Michael L. <he...@us...>]

Update of /cvsroot/bprocessor/model/src/net/sourceforge/bprocessor/model
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv7150/src/net/sourceforge/bprocessor/model

Added Files:
	History.java 
Log Message:
History of commands for handling undo/redo

--- NEW FILE: History.java ---
//---------------------------------------------------------------------------------
// $Id: History.java,v 1.1 2006/01/11 10:19:58 henryml Exp $
//
// Copyright (c) 2005      The BProcessor Team (http://bprocessor.sourceforge.net) 
// Released under the Lesser GNU Public License v2.1
//---------------------------------------------------------------------------------

package net.sourceforge.bprocessor.model;

import java.util.Stack;

/**
 * The History for containing commands for undo and redo support
 */
public class History {
  /** The undo stack */
  private Stack undoStack;
  
  /** The redo stack */
  private Stack redoStack;
  
  /** A singular history instance */
  private static History instance = new History();
  
  /**
   * Return the singular history instance
   * @return The history
   */
  public static History getInstance() {
    return instance;
  }
  
  /**
   * Constructor for History
   */
  public History() {
    undoStack = new Stack();
    redoStack = new Stack();
  }
  
  /**
   * Apply a command, clear the redo stack and
   * push the new command on the undo stack.
   * @param command The command to apply
   */
  public void apply(Command command) {
    command.apply();
    redoStack.clear();
    undoStack.push(command);
  }
  
  /**
   * Undo the command on top of undo stack and push
   * it on the redo stack
   */
  public void undo() {
    if (!undoStack.isEmpty()) {
      Command top = (Command) undoStack.pop();
      top.undo();
      redoStack.push(top);
    }
  }
  
  /**
   * Redo the command on top of redo stack and push
   * it on the undo stack
   */
  public void redo() {
    if (!redoStack.isEmpty()) {
      Command top = (Command) redoStack.pop();
      top.redo();
      undoStack.push(top);
    }
  }
  
  /**
   * Return the top of the undo stack or null if empty.
   * @return The top of the undo stack
   */
  public Command undoTop() {
    if (!undoStack.isEmpty()) {
      return (Command) undoStack.peek();
    } else {
      return null;
    }
  }
  
  /**
   * Return the top of the redo stack or null if empty.
   * @return The top of the redo stack
   */
  public Command redoTop() {
    if (!redoStack.isEmpty()) {
      return (Command) redoStack.peek();
    } else {
      return null;
    }
  } 
  
  /**
   * Clear this History
   */
  public void clear() {
    undoStack.clear();
    redoStack.clear();
  }
}