[Struts Wiki] Update of "StrutsCatalogDoUndoRedo" by MichaelJouravlev

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The following page has been changed by MichaelJouravlev:
http://wiki.apache.org/struts/StrutsCatalogDoUndoRedo

The comment on the change is:
orpahed; nothing more than a linked list.

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- StrutsCatalog: '''Provide a Do, Undo, Redo command pattern solution that can assist a workflow application.'''
+ deleted
  
- This is simple.  Here are the basic classes and then I will give the application itself, which is fairly straightforward.
- 
- {{{
- // COMMAND CLASS
- public interface Command {
-   public void doCommand();
-   public void undoCommand();
- }
- 
- // Do, Undo, and Redo COMMANDS
- public interface Do extends Command {}
- 
- public final class Undo implements Command {
-   public void doCommand() { return; }
-   public void undoCommand() { return; }
- }
- 
- public final class Redo implements Command {
-   public void doCommand() { return; }
-   public void undoCommand() { return; }
- }
- }}}
- 
- The following is the application class:
- 
- {{{
- public class UndoableList {
-   private int       maxHistory = 100;
-   private LinkedList   history = new LinkedList();
-   private LinkedList  redoList = new LinkedList();
- 
-   private UndoableList() {
-   }
- 
-   public static UndoableList getInstance() {
-   return new UndoableList();
-   }
- 
-   public void setMaxHistory(int maxHistory) {
-     this.maxHistory = maxHistory;
-   }
- 
-   public void invoke(Command command) {
-     if (command instanceof Undo) { undoCommand(); return; }
-     if (command instanceof Redo) { redoCommand(); return; }
- 
-     if (command instanceof Do) {
-       command.doCommand();
-       addToHistory(command);
-     } else {
-       history.clear();
-     }
- 
-     if (redoList.size() > 0) {
-       redoList.clear();
-     }
-   }
- 
-   private void undoCommand() {
-     if (history.size() > 0) {
-       Command undoCommand = (Command)history.removeFirst();
-       undoCommand.undoCommand();
-       redoList.addFirst(undoCommand);
-     }
-   }
- 
-   private void redoCommand() {
-     if (redoList.size() > 0) {
-       Command redoCommand = (Command)redoList.removeFirst();
-       redoCommand.doCommand();
-       history.addFirst(redoCommand);
-     }
-   }
- 
-   private void addToHistory(Command command) {
-     history.addFirst(command);
-     if (history.size() > maxHistory) {
-       history.removeLast();
-     }
-   }
- }
- }}}
- 
- You can clearly add to this or change this in a myriad of ways.
- 
- Enjoy!
- 
- Michael !McGrady
-     
- 

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