When to use super.paint(g) ?

Question

Hello everyone,
I have some issues in basic animations that I need to clear, I'd be very happy if you helped.
I have 3 applications in hand that work differently concerning refreshing of the images with the repaint() method. The two initial ones use timers to repaint, the last one (that I copied from "Learning Java") follows mouse dragging gestures -I don't know if it has to do anything with that, however.
The first one needs desperately a super.paint(g) line to erase older frames of a moving ball animation:
package cms_tp23;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class Balle extends JFrame implements ActionListener, KeyListener {
     JButton bNord = new JButton("Start!");
     JButton bSud = new JButton("Stop!");
     JPanel panel = new JPanel();
     Object source;
     Timer timer = new Timer(30,this);
     int hei = 300, wid = 300, x = 100, y = 65, count = 0;
     boolean flag1 = false, flag2 = false;
     char key;
     Color red = Color.RED, blue = Color.BLUE, aux = Color.BLUE;
     public Balle ()
          this.setTitle("Balle");
          this.setResizable(false);
          this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
          Toolkit tk = Toolkit.getDefaultToolkit();
          Dimension monitord = tk.getScreenSize();
          this.setBounds((monitord.width-wid)/2,(monitord.height-hei)/2, wid, hei);
          x = wid/2 - 20;
          Container cp = this.getContentPane();
          setVisible(true);
          bNord.addActionListener(this);
          bSud.addActionListener(this);
          bNord.addKeyListener(this);
          bSud.addKeyListener(this);
          add(bNord,BorderLayout.NORTH);
          add(bSud,BorderLayout.SOUTH);
          panel.setBackground(Color.WHITE);
          add(panel);
          bNord.requestFocus();
          setVisible(true);
     public void actionPerformed(ActionEvent e)
          source = e.getSource();
          if (source == bNord)
               timer.start();
          if (source == bSud)
               timer.stop();
          if (source == timer)
               repaint();
     public void keyPressed(KeyEvent ke)
     public void keyReleased(KeyEvent ke)
     public void keyTyped(KeyEvent ke)
          key = ke.getKeyChar();
          if (key == '\n')
               timer.start();
          if (key == '\u001B')
               timer.stop();
     public void paint(Graphics g)
          super.paint(g);
          g.setColor(aux);
          g.fillOval(x,y,40,40);
          if (y > hei - 69 || y < 61)
               flag1 = !flag1;
               aux = g.getColor();
               if (aux == red) aux = blue; else aux = red;
          if (!flag1) y = y+1;
          else y = y-1;
          if (x > wid-43 || x < 3)
               flag2 = !flag2;
               aux = g.getColor();
               if (aux == red) aux = blue; else aux = red;
          if (!flag2) x = x+1;
          else x = x-1;
     public static void main(String[] args) {
          Balle maBalle = new Balle();
}The second one doesn't display the backround color I've fixed if I don't use the super.paint(g) instruction:
//file: Fenetre.java
package cms_tp23;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class Fenetre extends JFrame implements ActionListener, KeyListener {
     JButton bNord = new JButton("Start!");
     JButton bSud = new JButton("Stop!");
     Object source;
     Timer timer = new Timer(1,this);
     int hei = 600, wid = 600;
     char key;
     static JLabel label = new JLabel("");
     public Fenetre()
          this.setTitle("Balle");
          this.setResizable(true);
          this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
          Toolkit tk = Toolkit.getDefaultToolkit();
          Dimension monitord = tk.getScreenSize();
          this.setBounds((monitord.width-wid)/2,(monitord.height-hei)/2, wid, hei);
          Container cp = this.getContentPane();
          this.setVisible(true);
          bNord.addActionListener(this);
          bSud.addActionListener(this);
          bNord.addKeyListener(this);
          bSud.addKeyListener(this);
          add(bNord,BorderLayout.NORTH);
          add(bSud,BorderLayout.SOUTH);
          Panneau panneau = new Panneau();
          panneau.setBackground(new Color(149,74,74));
          label.setForeground(Color.ORANGE);
          panneau.add(label);
          add(panneau);
          bNord.requestFocus();
          this.setVisible(true);
     public static void main(String[] args) {
          Fenetre fenetre = new Fenetre();
     public void actionPerformed(ActionEvent e) {
          source = e.getSource();
          if (source == bNord)
               aksiyon('1');
          if (source == bSud)
               aksiyon('2');
          if (source == timer)
               repaint();
     public void keyTyped(KeyEvent ke) {
          key = ke.getKeyChar();
          if (key == '\n')
               if (timer.isRunning()) aksiyon('2'); else aksiyon('1');
          if (key == '\u001B')
               timer.stop();
     public void aksiyon(char c)
          if (c == '1')
               timer.start();
          else if (c == '2')
               timer.stop();
     public void keyPressed(KeyEvent arg0) {
     public void keyReleased(KeyEvent arg0) {
//file: Panneau.java
package cms_tp23;
import java.awt.*;
import javax.swing.*;
import java.util.Date;
public class Panneau extends JPanel {
     double lastDate;
     double dt;
     double x;
     double y = 0;
     double x0;
     double y0;
     double vx;
     double vy;
     double vx0;
     double vy0 = 0;
     double gravite = 1;
     double frottement = 0.00;
     double diametre = 30;
     boolean firstjump = false;
     public void paint(Graphics g)
          super.paint(g);
          g.setColor(Color.GREEN);
          dt = 1;
          x = (getSize().width - diametre)/2;
          if (!firstjump)
               vy += vy0 + gravite*dt;
               vy *= 1 - frottement;
               y +=(y0 + vy*dt)/5.0f;
          else
               vy -= vy0 + gravite*dt;
               vy *= 1 - frottement;
               y -=(y0 + vy*dt)/500.0f;
               firstjump = false;
          g.fillOval((int)x,(int)y,(int)diametre,(int)diametre);
          if (y >= getSize().height - diametre && vy >= 0)
               vy = -vy;
               firstjump = true;
}And the third one (that I just rewrote) doesn't seem to need the famous line to work properly:
//file: HelloJava2
import java.awt.*;
import javax.swing.*;
public class HelloJava2  {
     public static void main(String[] args) {
          JFrame frame = new JFrame("Hello, Java!");
          HelloComponent hello = new HelloComponent("Hello Java!");
          frame.getContentPane().add(hello);
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setSize(new Dimension(300,300));
          frame.setVisible(true);
//file: HelloComponent
import javax.swing.*;
import java.awt.event.*;
import java.awt.Graphics;
class HelloComponent extends JComponent implements MouseMotionListener {
     String theMessage;
     int messageX = 100, messageY = 100;
     public HelloComponent(String message)
          theMessage = message;
          addMouseMotionListener(this);
     public void paintComponent(Graphics g) {
          g.drawString(theMessage, messageX, messageY);
     public void mouseDragged(MouseEvent arg0) {
          messageX = arg0.getX();
          messageY = arg0.getY();
          repaint();
     public void mouseMoved(MouseEvent arg0) {
}Now, if anyone could help me out... I hope the third one doesn't lead to a copyright infringement, I don't think it does.
Thanks.

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class BalleRx extends JFrame implements ActionListener, KeyListener {
    JButton bNord = new JButton("Start!");
    JButton bSud = new JButton("Stop!");
//    JPanel panel = new JPanel();
    Object source;
    char key;
    int hei = 300, wid = 300, x;
    BallePanel ballePanel;
    public BalleRx() {
        this.setTitle("Balle");
        this.setResizable(false);
        this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
        Toolkit tk = Toolkit.getDefaultToolkit();
        Dimension monitord = tk.getScreenSize();
        this.setBounds((monitord.width-wid)/2,(monitord.height-hei)/2, wid, hei);
        x = wid/2 - 20;
//        setVisible(true);
        bNord.addActionListener(this);
        bSud.addActionListener(this);
        bNord.addKeyListener(this);
        bSud.addKeyListener(this);
        ballePanel = new BallePanel();
//        Container cp = this.getContentPane();
        add(bNord,BorderLayout.NORTH);
        add(bSud,BorderLayout.SOUTH);
        // instead you can do cp.setbackground(...
//        panel.setBackground(Color.WHITE);
//        add(panel);
        add(ballePanel);
        bNord.requestFocus();
        setVisible(true);
    public void actionPerformed(ActionEvent e) {
        source = e.getSource();
        if (source == bNord)
            ballePanel.start();
        if (source == bSud)
            ballePanel.stop();
    public void keyTyped(KeyEvent ke) {
        key = ke.getKeyChar();
        if (key == '\n')
            ballePanel.start();
        if (key == '\u001B')    // KeyEvent.VK_ESCAPE
            ballePanel.stop();
    public void keyPressed(KeyEvent ke) { }
    public void keyReleased(KeyEvent ke) { }
    public static void main(String[] args) {
        BalleRx maBalle = new BalleRx();
class BallePanel extends JPanel implements ActionListener {
    Timer timer = new Timer(30,this);
    int x = 100, y = 65, count = 0, DIA = 40;
    boolean flag1 = false, flag2 = false;
    Color red = Color.RED, blue = Color.BLUE, aux = Color.BLUE;
    public void actionPerformed(ActionEvent e) {
        repaint();
    protected void paintComponent(Graphics g) {
        // this clears the background
        // (if you don't you get artifacts)
        super.paintComponent(g);
        // or you can do this to clear it
        //((Graphics2D)g).setBackground(Color.white);
        //g.clearRect(0, 0, getWidth(), getHeight());
        // or this
        //g.setColor(Color.white);
        //g.fillRect(0, 0, getWidth(), getHeight());
        g.setColor(aux);
        g.fillOval(x,y,DIA,DIA);
//        if (y > hei - 69 || y < 61) {    // no insets to mess with
        if (y > getHeight() - DIA || y < 0) {
            flag1 = !flag1;
            aux = g.getColor();
            if (aux == red) aux = blue; else aux = red;
        if (!flag1) y = y+1;
        else y = y-1;
        if (x > getWidth() - DIA || x < 3) {
            flag2 = !flag2;
            aux = g.getColor();
            if (aux == red) aux = blue; else aux = red;
        if (!flag2) x = x+1;
        else x = x-1;
    public void start() {
        if(!timer.isRunning())
            timer.start();
    public void stop() {
        timer.stop();
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class FenetreRx extends JFrame implements ActionListener, KeyListener {
    JButton bNord = new JButton("Start!");
    JButton bSud = new JButton("Stop!");
    Object source;
    Timer timer = new Timer(1,this);
    int hei = 600, wid = 600;
    char key;
    static JLabel label = new JLabel("");
    public FenetreRx() {
        this.setTitle("Balle");
        this.setResizable(true);
        this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
        Toolkit tk = Toolkit.getDefaultToolkit();
        Dimension monitord = tk.getScreenSize();
        this.setBounds((monitord.width-wid)/2,(monitord.height-hei)/2, wid, hei);
//        Container cp = this.getContentPane();
//        this.setVisible(true);
        bNord.addActionListener(this);
        bSud.addActionListener(this);
        bNord.addKeyListener(this);
        bSud.addKeyListener(this);
        add(bNord,BorderLayout.NORTH);
        add(bSud,BorderLayout.SOUTH);
        PanneauRx panneau = new PanneauRx();
        panneau.setBackground(new Color(149,74,74));
        label.setForeground(Color.ORANGE);
        panneau.add(label);
        add(panneau);
        bNord.requestFocus();
        this.setVisible(true);
    public static void main(String[] args) {
        FenetreRx fenetre = new FenetreRx();
    public void actionPerformed(ActionEvent e) {
        source = e.getSource();
        if (source == bNord)
            aksiyon('1');
        if (source == bSud)
            aksiyon('2');
        if (source == timer)
            repaint();
    public void keyTyped(KeyEvent ke) {
        key = ke.getKeyChar();
        if (key == '\n')
            if (timer.isRunning()) aksiyon('2'); else aksiyon('1');
        if (key == '\u001B')
            timer.stop();
    public void aksiyon(char c) {
        if (c == '1') {
            timer.start();
        else if (c == '2') {
            timer.stop();
    public void keyPressed(KeyEvent arg0)  { }
    public void keyReleased(KeyEvent arg0) { }
class PanneauRx extends JPanel {
    double lastDate;
    double dt;
    double x;
    double y = 0;
    double x0;
    double y0;
    double vx;
    double vy;
    double vx0;
    double vy0 = 0;
    double gravite = 1;
    double frottement = 0.00;
    double diametre = 30;
    boolean firstjump = false;
    public void paintComponent(Graphics g) {
        // draws the default JPanel background including
        // any background color you may have set
        super.paintComponent(g);
        // if you like you can omit the call to
        // super.paintComponent and fill in the
        // background yourself with:
        //g.setColor(Color.pink);
        //g.fillRect(0, 0, getWidth(), getHeight());
        // or with:
        //((Graphics2D)g).setBackground(Color.red);
        //g.clearRect(0, 0, getWidth(), getHeight());
        g.setColor(Color.GREEN);
        dt = 1;
        x = (getSize().width - diametre)/2;
        if (!firstjump) {
            vy += vy0 + gravite*dt;
            vy *= 1 - frottement;
            y +=(y0 + vy*dt)/5.0f;
        else {
            vy -= vy0 + gravite*dt;
            vy *= 1 - frottement;
            y -=(y0 + vy*dt)/500.0f;
            firstjump = false;
        g.fillOval((int)x,(int)y,(int)diametre,(int)diametre);
        if (y >= getSize().height - diametre && vy >= 0) {
            vy = -vy;
            firstjump = true;
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics;
import javax.swing.*;
public class HJ2 {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Hello, Java!");
        HC hello = new HC("Hello Java!");
        frame.getContentPane().add(hello);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(300,300));
        frame.setVisible(true);
* using JComponent here is tricky because it is non-opaque
class HC extends JComponent implements MouseMotionListener {
    String theMessage;
    int messageX = 100, messageY = 100;
    public HC(String message) {
        theMessage = message;
        setOpaque(true);
        addMouseMotionListener(this);
    protected void paintComponent(Graphics g) {
        // JComponent is non-opaque
        // so it doesn't do anything with this
        //super.paintComponent(g);
        // now we're left to our own devices
        // see what happens without these next 2 lines
        g.setColor(getBackground());
        g.fillRect(0, 0, getWidth(), getHeight());
        g.setColor(Color.black);
        g.drawString(theMessage, messageX, messageY);
    public void mouseDragged(MouseEvent arg0) {
        messageX = arg0.getX();
        messageY = arg0.getY();
        repaint();
    public void mouseMoved(MouseEvent arg0) { }
}