Designing and Implementing Undo / Item-Level Undo

1. How do you implement undo functionality?
2. How do you implement undo in Python?
3. How will you implement undo and redo option using the data structure?
4. How do you implement undo and redo in Java?

How do you implement undo functionality?

If “UNDO” string is encountered, pop the top element from Undo stack and push it to Redo stack. If “REDO” string is encountered, pop the top element of Redo stack and push it into the Undo stack. If “READ” string is encountered, print all the elements of the Undo stack in reverse order.

How do you implement undo in Python?

Most Python commands which affect the underlying state of an object create an undo/redo action which can then be undone or redone through Python or through the Edit > Undo and Redo menu items.

How will you implement undo and redo option using the data structure?

Which data structure is used in redo-undo feature? Explanation: Stack data structure is most suitable to implement redo-undo feature. This is because the stack is implemented with LIFO(last in first out) order which is equivalent to redo-undo feature i.e. the last re-do is undo first.

How do you implement undo and redo in Java?

You have to define undo(), redo() operations along with execute() in Command interface itself . Define a State in your ConcreteCommand class. Depending on current State after execute() method, you have to decide whether command should be added to Undo Stack or Redo Stack and take decision accordingly.