Repaint () method calling in another class

Question

I have a problem with the repaint() method in my Java . I want to call it in another class , but I cannot, something is not working at all. I searched the forums, but couldn’t help me.

My main class :

 public class Main { public static Main main; public static JFrame f; public Main(){ } public static void main(String[] args) { main = new Main(); f = new JFrame(); Ball b = new Ball(); f.getContentPane().setBackground(Color.GRAY); f.add(b); f.setSize(500, 500); f.setLocationRelativeTo(null); f.setTitle("Test"); f.setVisible(true); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.addMouseMotionListener(b); f.addKeyListener(new Key()); } } 

Ball class where I created 2DGraphics to move shapes:

 public class Ball extends JLabel implements MouseMotionListener{ public Ball(){ } public static double x = 10; public static double y = 10; public static double width = 40; public static double height = 40; String nick; boolean isEllipse = true; public void paintComponent(Graphics g){ super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; if(isEllipse){ Ellipse2D e2d = new Ellipse2D.Double(x, y, width, height); g2d.setColor(Color.RED); g2d.fill(e2d); } else{ Rectangle2D r2d = new Rectangle2D.Double(x, y, width, height); g2d.setColor(Color.GREEN); g2d.fill(r2d); } } @Override public void mouseDragged(MouseEvent e) { isEllipse = false; x = e.getX() - 30; y = e.getY() - 40; this.repaint(); } @Override public void mouseMoved(MouseEvent e) { x = e.getX() - 30; y = e.getY() - 40; isEllipse = true; this.repaint(); } } 

And the Key class , where I put the KeyListener to move the shapes with a keystroke:

 public class Key extends Ball implements KeyListener { public Key() { } @SuppressWarnings("static-access") @Override public void keyPressed(KeyEvent e) { if(e.getKeyCode() == KeyEvent.VK_W){ super.x += 10; super.repaint(); System.out.println("x: " + super.x); } } @Override public void keyReleased(KeyEvent e) { // TODO Auto-generated method stub } @Override public void keyTyped(KeyEvent e) { // TODO Auto-generated method stub } } 

But something is wrong with this code: the super method does not work for the Key class . Everything in the Ball class works well. Where is the problem?

Answer 1

Super works fine, but your interpretation of what it does is incorrect. Your problem is that you are trying to use inheritance to solve a problem that is not resolved with inheritance. You should call repaint() actual rendered and used instance of Ball, and not an instance of some completely different Key class that is inadequately distributed from Ball. First, make Key not continue Ball, go to the true link to Ball in Key and the solution will fall from that.

Maybe do something like this:

 f.addKeyListener(new Key(b)); 

and

 public class Key implements KeyListener { private Ball ball; public Key(Ball ball) { this.ball = ball; } public void keyPressed(KeyEvent e) { if(e.getKeyCode() == KeyEvent.VK_W){ b.incrX(10); // give Ball a public method for this b.repaint(); // System.out.println("x: " + super.x); } } // .... etc... 

Note that I would use Key Bindings for this and not KeyListener, since then I would not have to futz with keyboard focus.

For instance:

 import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Point; import java.awt.RenderingHints; import java.awt.event.*; import javax.swing.AbstractAction; import javax.swing.ActionMap; import javax.swing.InputMap; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.KeyStroke; import javax.swing.SwingUtilities; public class MoveBall { private static final int PREF_W = 500; private static final int PREF_H = PREF_W; private static void createAndShowGui() { BallPanel ballPanel = new BallPanel(PREF_W, PREF_H); MyMouse myMouse = new MyMouse(ballPanel); ballPanel.addMouseListener(myMouse); ballPanel.addMouseMotionListener(myMouse); new CreateKeyBindings(ballPanel); JFrame frame = new JFrame("MoveBall"); frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); frame.getContentPane().add(ballPanel); frame.pack(); frame.setLocationByPlatform(true); frame.setVisible(true); } public static void main(String[] args) { SwingUtilities.invokeLater(() -> { createAndShowGui(); }); } } @SuppressWarnings("serial") class BallPanel extends JPanel { private static final Color ELLIPSE_COLOR = Color.RED; private static final Color SQUARE_COLOR = Color.GREEN; private static final int BALL_WIDTH = 40; private int prefW; private int prefH; private boolean isEllipse = true; private int ballX; private int ballY; public BallPanel(int prefW, int prefH) { this.prefW = prefW; this.prefH = prefH; } public boolean isEllipse() { return isEllipse; } public void setEllipse(boolean isEllipse) { this.isEllipse = isEllipse; } public int getBallX() { return ballX; } public void setBallX(int ballX) { this.ballX = ballX; } public void setXY(int x, int y) { ballX = x; ballY = y; repaint(); } public void setXYCenter(int x, int y) { ballX = x - BALL_WIDTH / 2; ballY = y - BALL_WIDTH / 2; repaint(); } public void setXYCenter(Point p) { setXYCenter(px, py); } public int getBallY() { return ballY; } public void setBallY(int ballY) { this.ballY = ballY; } public void incrementBallX(int x) { ballX += x; repaint(); } public void incrementBallY(int y) { ballY += y; repaint(); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D) g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); if (isEllipse) { g2.setColor(ELLIPSE_COLOR); g2.fillOval(ballX, ballY, BALL_WIDTH, BALL_WIDTH); } else { g2.setColor(SQUARE_COLOR); g2.fillOval(ballX, ballY, BALL_WIDTH, BALL_WIDTH); } } @Override public Dimension getPreferredSize() { if (isPreferredSizeSet()) { return super.getPreferredSize(); } return new Dimension(prefW, prefH); } } class MyMouse extends MouseAdapter { private BallPanel ballPanel; public MyMouse(BallPanel ballPanel) { this.ballPanel = ballPanel; } @Override public void mousePressed(MouseEvent e) { ballPanel.setXYCenter(e.getPoint()); } @Override public void mouseDragged(MouseEvent e) { ballPanel.setXYCenter(e.getPoint()); } @Override public void mouseReleased(MouseEvent e) { ballPanel.setXYCenter(e.getPoint()); } } enum Direction { UP(KeyEvent.VK_UP), DOWN(KeyEvent.VK_DOWN), LEFT(KeyEvent.VK_LEFT), RIGHT(KeyEvent.VK_RIGHT); private int key; private Direction(int key) { this.key = key; } public int getKey() { return key; } } // Actions for the key binding @SuppressWarnings("serial") class MyKeyAction extends AbstractAction { private static final int STEP_DISTANCE = 5; private BallPanel ballPanel; private Direction direction; public MyKeyAction(BallPanel ballPanel, Direction direction) { this.ballPanel = ballPanel; this.direction = direction; } @Override public void actionPerformed(ActionEvent e) { switch (direction) { case UP: ballPanel.incrementBallY(-STEP_DISTANCE); break; case DOWN: ballPanel.incrementBallY(STEP_DISTANCE); break; case LEFT: ballPanel.incrementBallX(-STEP_DISTANCE); break; case RIGHT: ballPanel.incrementBallX(STEP_DISTANCE); break; default: break; } } } class CreateKeyBindings { private BallPanel ballPanel; public CreateKeyBindings(BallPanel ballPanel) { this.ballPanel = ballPanel; int condition = JComponent.WHEN_IN_FOCUSED_WINDOW; InputMap inputMap = ballPanel.getInputMap(condition); ActionMap actionMap = ballPanel.getActionMap(); for (Direction direction : Direction.values()) { KeyStroke keyStroke = KeyStroke.getKeyStroke(direction.getKey(), 0); String keyString = keyStroke.toString(); inputMap.put(keyStroke, keyString); actionMap.put(keyString, new MyKeyAction(ballPanel, direction)); } } }