Undo operation using ArrayList

Question

I want to implement undo and redo operation for my paint application.

I created class which extends from jpanel and here i have arraylist to keep all the elements on my jpanel.

This how it works when i add new element (f.e i draw something with pencil tool):

this.elements.add(new PencilElement(this.tool.getPPoint(), this.tool.getCPoint(), this.tool.getColor(), this.tool.getStroke()));

I want to use another arraylist to keep copy of all elements and when i click "undo" button: -->last element from temporary array list would be removed -->content of base arraylist (in this case "elements" arraylist) would be replaced by this temporary arraylist content.

If you have another ideas, please share

Thanks!

Look at http://docs.oracle.com/javase/7/docs/api/java/util/Stack.html — bobbel, Oct 31 '14 at 12:12
the classical pattern for undo - http://en.wikipedia.org/wiki/Command_pattern — Leo, Oct 31 '14 at 12:12

score 0 · Answer 1 · answered Oct 31 '14 at 12:28

0

When you want to make a redo, then you should not delete the last element from the second ArrayList, because you will need it for the redo.

answered Oct 31 '14 at 12:28

Patricia

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score 0 · Accepted Answer · edited May 23 '17 at 11:49

Create a stack using Deque (Why should I use Deque over Stack?)

A suggestion is to use a stack for the actions also, so you simply can pop from the ordinary action stack and push on the undo stack, and the other way around when making a redo.

//suggestion for current solution

private Deque<PencilElement> undoStack = new ArrayDeque<PencilElement>();

//whenUndo
undoStack.addFirst(myPencilElement);

//whenRedo
elements.add(undoStack.removeFirst());


//New suggestion
//whenUndo
undoStack.addFirst(elements.removeFirst());

//whenRedo
elements.add(undoStack.removeFirst());

also make sure to disable redo when no actions on the stack

Undo operation using ArrayList

2 Answers2