Java Graphics2D moving object stopped in the middle

Question

I'm having a hard time to figure out why this moving rectangle is stopped right in the middle of the Jpanel. The Timer is not stopped, seems there is a boundary in the middle. Anyone could explain it for me please? and how can I make it move the whole way (800)?

here is my code:

public class TestDemo extends JPanel implements ActionListener {
  private static final long serialVersionUID = 1L;
  private int x;
  private int y;
  Timer timer;

TestDemo() {
    x = 0;
    y = 0;
    this.setBackground(Color.BLACK);
    timer = new Timer(10, this);
    timer.start();
}

public void paint(Graphics g) {
    super.paint(g);
    Graphics2D g2d = (Graphics2D) g;
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
    g2d.scale(1, 1);
    g2d.setPaint(Color.RED);
    g2d.fill(new Rectangle2D.Double(getX(), getY(), 20, 20));
}

public void actionPerformed(ActionEvent e) {
    setX(getX() + 1);
    repaint();
}

public static void main(String[] args) {
    JFrame frame = new JFrame("Moving star");
    JPanel testDemo = new TestDemo();
    testDemo.setSize(800, 200);
    frame.add(testDemo);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(800, 600);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

public int getX() {
    return x;
}
public void setX(int x) {
    this.x = x;
}
public int getY() {
    return y;
}
public void setY(int y) {
    this.y = y;
}
}

Answer 1

1. The code is overriding methods that already exist and are used for other purposes. That is the main problem.
2. For custom painting any JComponent, use paintComponent(..) rather than paint(..)

Here is the (working) code with both changes implemented.

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

public class TestDemo extends JPanel implements ActionListener {

    private static final long serialVersionUID = 1L;
    private int x1;
    private int y1;
    Timer timer;

    TestDemo() {
        x1 = 0;
        y1 = 0;
        this.setBackground(Color.BLACK);
        timer = new Timer(10, this);
        timer.start();
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        g2d.scale(1, 1);
        g2d.setPaint(Color.RED);
        g2d.fill(new Rectangle2D.Double(getX1(), getY1(), 20, 20));
    }

    public void actionPerformed(ActionEvent e) {
        setX1(getX1() + 1);
        repaint();
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Moving star");
        JPanel testDemo = new TestDemo();
        testDemo.setSize(800, 200);
        frame.add(testDemo);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 600);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public int getX1() {
        return x1;
    }

    public void setX1(int x1) {
        this.x1 = x1;
    }

    public int getY1() {
        return y1;
    }

    public void setY1(int y1) {
        this.y1 = y1;
    }
}