Undo functionality in JTextArea

Question

I am trying to implement undo functionality in JTextArea. Googled for tutorial and followed one of the tutorial and wrote the below code. The event is triggered

Answer 1

I'm not sure but maybe you can not addKeyListener for your gui.
For example;

class Example implements KeyListener{

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  this.addKeyListener(this); // if want to add key listener for main container

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}

this is about how to use key listener.