Cannot use MouseEvents in main

Question

What I'm trying to do

Making a Pong game where the Y axis gets the value from my cursor according to the application

What did I tried

private void pallet() {
    ycur=(int)MouseInfo.getPointerInfo().getLocation().getY();
}

This way I get the Y value according to my monitor instead of the application.

I also tried to use the MouseEvent.getY(), but I get the error when trying to call this method from the main.

private void pallet() {
    ycur=(int)MouseInfo.getPointerInfo().getLocation().getY();
}

This is how my code looks like, I think the problem lies in how I'm using my main and methods but I'm not sure.

public class MyFirst extends JPanel {

    public int x = 500, y = 300, border = 30;
    public boolean goingDown = true;
    public int ycur, cursor;


    public void moveBall() {
        x++;
        if (goingDown == true) {
            y++;
        } else if (goingDown == false) {
            y--;
        }

        if (y == getHeight() - border) {
            goingDown = false;
        } else if (y == 0) {
            goingDown = true;
        }
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        g.fillOval(x, y, 30, 30);
        g.fillRect(30, ycur, 15, 100);
    }

    public static void main(String[] args) throws InterruptedException     {
        JFrame frame = new JFrame("Pong");
        frame.pack();
        frame.setSize(1000, 600);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);

        MyFirst game = new MyFirst();
        frame.add(game);
        while (true) {
            game.pallet(e);
            game.moveBall();
            game.repaint();
            Thread.sleep(10);
        }
    }

    public void pallet(MouseEvent e) {
        ycur=e.getY();
    }

}

When im using the MouseEvent, i get an error at game.pallet(e); in the main, saying that it doesnt recognise 'e'. — creativename, Dec 13 '16 at 17:03
Right, so your error is on this line: `game.pallet(e);` because `e` isn't defined anywhere. — Matthew Brzezinski, Dec 13 '16 at 17:05
Swing is event driven, so use a `MouseListener` instead of this ugly infinite loop. — , Dec 13 '16 at 17:06
You don't want to use mouse in main. Your design is broken. Instead add a MouseListener to the JPanel and use that. — Hovercraft Full Of Eels, Dec 13 '16 at 17:06
Edit: yep, just as @Paul says -- you're fighting against event-driven design rather than working with it. — Hovercraft Full Of Eels, Dec 13 '16 at 17:06
I would look here, https://docs.oracle.com/javase/7/docs/api/java/awt/event/MouseListener.html add in a `MouseListener` to your JPanel and it will handle input for you. — Matthew Brzezinski, Dec 13 '16 at 17:06
@user123: no such thing as a `MouseActionListener". He should use a MouseListener or a MouseMotionListener, or combine them with a MouseAdapater that is used as both. — Hovercraft Full Of Eels, Dec 13 '16 at 17:07

score 2 · Accepted Answer · answered Dec 13 '16 at 17:29

Problems with your code:

As already mentioned, you're fighting against Swing's event-driven architecture. Instead of a while true loop, use listeners, including a MouseMotionListener ot track the changes in the mouse location, and an ActionListener tied to a Swing Timer to move the ball.
Avoid using Thread.sleep(...) in Swing GUI's except with great care as this can put the entire application to sleep.
Avoid putting too much logic within the main method. This method should be short, should create the key objects, connect them, set the program in motion and that's it.
Paint with the paintComponent method, not the paint method. It results in smoother animation with its double buffering.

For example:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.*;

@SuppressWarnings("serial")
public class MoveBallTest extends JPanel{
    private static final int PREF_W = 1000;
    private static final int PREF_H = 600;
    private static final int TIMER_DELAY = 12;
    private static final int SPRITE_WIDTH = 30;
    private static final Color OVAL_SPRITE_COLOR = Color.RED;
    private static final Color RECT_SPRITE_COLOR = Color.BLUE;
    private static final int DELTAY_Y = 1;
    private boolean goingDown = true;
    private Timer timer = new Timer(TIMER_DELAY, this::timerActionPerformed);
    private int ovalSpriteY;
    private int rectSpriteY;

    public MoveBallTest() {
        timer.start();
        MyMouse myMouse = new MyMouse();
        addMouseMotionListener(myMouse);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(OVAL_SPRITE_COLOR);
        g.fillOval(SPRITE_WIDTH, ovalSpriteY, SPRITE_WIDTH, SPRITE_WIDTH);
        g.setColor(RECT_SPRITE_COLOR);
        g.fillRect(SPRITE_WIDTH, rectSpriteY, SPRITE_WIDTH / 2, SPRITE_WIDTH * 3);
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    public void timerActionPerformed(ActionEvent e) {
        if (ovalSpriteY <= 0) {
            goingDown = true;
        } else if (ovalSpriteY >= getHeight() - SPRITE_WIDTH) {
            goingDown = false;
        }

        ovalSpriteY += goingDown ? DELTAY_Y : -DELTAY_Y;
        repaint();
    }

    private class MyMouse extends MouseAdapter {
        @Override
        public void mouseMoved(MouseEvent e) {
            rectSpriteY = e.getY();
        }
    }

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

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

@creativename: http://stackoverflow.com/questions/798545/what-is-the-java-operator-called-and-what-does-it-do — Hovercraft Full Of Eels, Dec 13 '16 at 17:53

Cannot use MouseEvents in main

1 Answers1