What is the secret of transparency in Java Swing?

Question

Java

Good Time! I am learning java and now swing in particular. I stumbled upon this on the internet

example

import javax.swing.JFrame;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;

import com.sun.awt.AWTUtilities;
   
  public class TransparentFrame extends JFrame {
       public TransparentFrame() {
           setTitle("Transparent Frame");
           setSize(400,400);
           setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           JSlider slider = new JSlider(JSlider.HORIZONTAL, 10, 100, 50);
           
           add(slider);
           setVisible(true);
       }
       public static void main(String[] args) {
      	 
          new TransparentFrame();
            
           
       }
       
       public void stateChanged(ChangeEvent e) {
   	      JSlider slider = (JSlider) e.getSource();
   	      if(!slider.getValueIsAdjusting()){
   	    	 AWTUtilities.setWindowOpacity(TransparentFrame.this, slider.getValue()/100f);
   	      }
   	}
  }

According to the author's idea, it should turn out like this

So

but in fact it turns out

So

Ie transparency does not work. Tell me what is wrong and how to implement it correctly?
Thanks in advance!

Answer 1

Try moving the code from the stateChanged method to the slider listener. That is, before
add(slider)write

slider.addActionListener(new ActionListener()
{
    @Override
    public void ActionPerformed(ActionEvent e)
    {
//Сюда
    }
}