How to know when a component resized

We use button as component in this example.

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COMPLETE SOURCE CODE FOR : HowToKnowWhenComponentResize.java
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import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

import java.awt.event.ComponentListener;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;

import java.awt.Component;

public class HowToKnowWhenComponentResize
{
 JFrame b=new JFrame("TRY RESIZE ME");
 
 JButton d=new JButton("MONSTER");
 
 public HowToKnowWhenComponentResize()
 {
  ComponentListener cl=new ComponentAdapter()
  {
   public void componentResized(ComponentEvent evt)
   {
    Component temp=(Component)evt.getSource();
    int currentWidth=temp.getSize().width;
    int currentHeight=temp.getSize().height;
    JOptionPane.showMessageDialog(null,"SIZE OF COMPONENT IS CHANGE\nMONSTER WIDTH NOW : "+currentWidth+"\nMONSTER HEIGHT NOW : "+currentHeight,"MONSTER'S SIZE",JOptionPane.INFORMATION_MESSAGE);
   }
  };
  
  d.addComponentListener(cl);
  b.add(d);
  
  b.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  b.setSize(400,100);
  b.setVisible(true);
 }
 
 public static void main(String[]args)
 {
  HowToKnowWhenComponentResize myObject=new HowToKnowWhenComponentResize();
 }
}

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JUST COMPILE AND EXECUTE IT
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