How to define a java component so that it works with a mouselistener

Question

I have a Ball class which I want to have extend JComponent and implement mouseListener.

public class Ball extends JComponent implements MouseListener {
    Int x, y, radius;

    public Ball(int X, int Y, int Radius){
        //contains only three ints and redefines x,y,radius
        x=X;
        y=Y;
        radius=Radius;
    }

    public void draw(Graphics g){
        //draw oval using x,y,radius
    }

    //5 mouselisteners undefined yet
}

So ball is the constructor which is used by a panel which is within a frame.

Sorry I have not yet entered all the code. I will submit my complete code soon.

So what I would have to do is use MouseEntered listener in the ball class so that when the mouse enters the component (the ball/oval) . But I don't know how to define the component so that it knows it has been entered. Does it need some dimensions? Because all I am doing is using the draw function in a panel.

I slightly formatted your code as your version just won't compile ('Public' vs 'public'). Variable assignment in the constructor is still wrong or at least does not make sense (X=x). Please revisit your code! — home, Feb 22 '12 at 15:16
Sorry i was entering the code on my phone and it automatically capitalizes things. — SoluableNonagon, Feb 22 '12 at 15:39

score 3 · Accepted Answer · answered Feb 22 '12 at 16:37

If this were my class, I wouldn't have it extend JComponent and wouldn't give it a MouseListener or MouseMotionListener especially if I wanted to display multiple balls in a single JComponent. Instead I would give it public methods that allow other classes to get its boundaries (such as is available from the Shape interface), and whether something is contained in the shape or not (again the Shape interface works well for this), and other public methods that allow outside classes to change the state (appearance?) of this object.

I would then have a JComponent hold one Ball or an ArrayList<Ball>, and in the MouseListener/MouseMotionListener/MouseAdapter for this JComponent, iterate through the ArrayList<Ball> seeing if the mouse is inside of any ball, and if so, change that ball's state. Then in the JComponent's paintComponent method, I'd iterate through the ArrayList<Ball> calling draw(g) on each Ball contained.

Thank you for the suggestion but I already was able to do it in that way by having another class modify the ball by reading the coordinates with a motion listener. — SoluableNonagon, Feb 22 '12 at 17:23
But now I need to define the ball as a component and it needs a mouse listener and to repaint the ball when the mouse enters it. I no longer am allowed to use a motion listener. — SoluableNonagon, Feb 22 '12 at 17:26

score 1 · Answer 2 · edited Feb 22 '12 at 15:16

1

You should call

this.addMouseListener(new MouseAdapter() {
    ....
});

in the constructor. Override mouseEntered() and mouseExited() inside of the adapter.

edited Feb 22 '12 at 15:16

DNA

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answered Feb 22 '12 at 15:13

Konstantin Solomatov

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score 0 · Answer 3 · answered Feb 22 '12 at 15:24

I would prefer that you implement the whole MouseListener. It could be possible that you want later more from your Ball-Component, like for example that it moves if you click on it or something. If you implement the interface you are applicable for later changes.

import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JComponent;

public class Ball extends JComponent implements MouseListener {
    int x, y, radius;

    public Ball(int x, int y, int radius){
    //contains only three ints and redefines x,y,radius
    this.x= x;
    this.y= y;
    this.radius= radius;
}

public void draw(Graphics g){
    //draw oval using x,y,radius
}

@Override
public void mouseClicked(MouseEvent arg0) {


}

@Override
public void mouseEntered(MouseEvent arg0) {
    //your code to do things, when the mouse entered your ball          
}

@Override
public void mouseExited(MouseEvent arg0) {


}

@Override
public void mousePressed(MouseEvent arg0) {


}

@Override
public void mouseReleased(MouseEvent arg0) {


}

}

By the way this has another advantage. If you have a subclass of your "Ball" Component, for example a "RotatingBall". You can easily extends your existing Ball Class and override the behaviour of the MouseListener — Jan Koester, Feb 22 '12 at 15:26

score 0 · Answer 4 · answered Feb 22 '12 at 18:21

Besides the remarks already made by Hovercraft Full Of Eels, I think you confuse the concept of a being a listener, and adding a listener to something.

It is not by implementing MouseListener that those methods will be called. A listener is the interested party and you add it to the object in which you are interested. So in this case you want to add a MouseListener to your Ball class, which is completely different from letting your Ball class implement MouseListener.

More information can be found on Wikipedia: Observer pattern or a more simple and more Swing oriented document can be found in the Swing tutorials

How to define a java component so that it works with a mouselistener

4 Answers4