Redraw () does not clear the frame

Question

public class Graphics2DTest extends JPanel implements ActionListener{
private Timer time = new Timer(5,(ActionListener) this);
int x = 0,y = 0;
public void paintComponent(Graphics g){

    Graphics2D gui = (Graphics2D) g;
    Rectangle2D rectangle = new Rectangle2D.Double(x,y,100,150);
    gui.setPaint(Color.GREEN);
    gui.fill(rectangle);
    time.start();
}

public void actionPerformed(ActionEvent arg0) {
    x++;
    y++;
    repaint();
}
}

The problem is that repaint () should clear the frame and draw a rectangle in position, but the previously colored rectangle remains. So how to do this? Please explain your answers.

Answer 1

Have you tried calling super.paintComponent (g) in the paintComponent method? This will clear the previous images made in your JPanel:

public void paintComponent(Graphics g){
  super.paintComponent(g);
  Graphics2D gui = (Graphics2D) g;
  Rectangle2D rectangle = new Rectangle2D.Double(x,y,100,150);
  gui.setPaint(Color.GREEN);
  gui.fill(rectangle);
  //time.start();
}

Also, do not start the timer or any program logic in the paintComponent method. First of all, you cannot absolutely control when or the method will be called, and, secondly, this method should only concern painting and nothing else and should be as fast as possible.

For instance:

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;

import javax.swing.*;

public class Graphics2DTest extends JPanel implements ActionListener {
    private Timer time = new Timer(5, (ActionListener) this);
    int x = 0, y = 0;

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D gui = (Graphics2D) g;
        Rectangle2D rectangle = new Rectangle2D.Double(x, y, 100, 150);
        gui.setPaint(Color.GREEN);
        gui.fill(rectangle);
        //time.start();
    }

    public void actionPerformed(ActionEvent arg0) {
        x++;
        y++;
        repaint();
    }

    public Graphics2DTest() {
        setPreferredSize(new Dimension(700, 500));
        time.start();
    }

    private static void createAndShowUI() {
        JFrame frame = new JFrame("Graphics2DTest");
        frame.getContentPane().add(new Graphics2DTest());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                createAndShowUI();
            }
        });
    }
}

Answer 2

. , , .

Answer 3

First you need to clear the background.

The resource is as follows:

http://java.sun.com/products/jfc/tsc/articles/painting/