Java JFrame create transparent window opacity animation

Description

Java JFrame create transparent window opacity animation 

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public  class Main extends JPanel {
   JFrame frameParent;//from ww w  .  j  a  v  a 2 s .com
   boolean focusWindow = false;
   private static float EXIT_WINDOW_OPACITY = .60f;

   public Main() {
       final JButton animButton = new JButton("<html><font size=+2>Press Me!</font>");
       animButton.addActionListener(new ActionListener() {
          @Override
          public void actionPerformed(ActionEvent e) {
              System.exit(0);
          }
      });
      add(animButton);
   }
   public void apply(JFrame frame) {
       frameParent = frame;
       frame.setUndecorated(true);
       frame.setOpacity(EXIT_WINDOW_OPACITY);
       frame.addMouseListener(new MouseAdapter() {
           int animDuration = 400;
           long startTime;
           Timer timer = new Timer(30, new ActionListener() {
               @Override
               public void actionPerformed(ActionEvent e) {
                   long currentTime = System.nanoTime() / 1000000;
                   long totalTime = currentTime - startTime;
                   if (totalTime > animDuration) {
                       startTime = currentTime;
                       timer.stop();
                       return;
                   }

                   // interpolate 
                   float fraction = (float) totalTime / animDuration;
                   if (frameParent != null) {
                       float newOpacity = frameParent.getOpacity();
                       if (focusWindow) {
                           newOpacity += fraction;
                       } else {
                           newOpacity -= fraction;
                       }
                       if (newOpacity > 1f) {
                           newOpacity = 1f;
                           timer.stop();
                       } else if (newOpacity < EXIT_WINDOW_OPACITY) {
                           newOpacity = EXIT_WINDOW_OPACITY;
                           timer.stop();
                       }
                       frameParent.setOpacity(newOpacity);

                   }
                   repaint();
               }
           });

           @Override
           public void mouseEntered(MouseEvent e) {
               focusWindow = true;
               startTime = System.nanoTime() / 1000000;
               timer.start();
           }

           @Override
           public void mouseExited(MouseEvent e) {
               focusWindow = false;
               startTime = System.nanoTime() / 1000000;
               timer.start();
           }
       });

   }

   public static void main(String[] args) {
      JFrame frame = new JFrame("java2s.com");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      Main Main = new Main();
      frame.add(Main);
      Main.apply(frame); 
      frame.setSize(300, 210);
      frame.setVisible(true);
   }
}



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