Associating a MouseListener with a JComponent

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My question here is that when the local class MouseClickListener calls the moveTo method of the comp object before we do: comp.addMouseListener(listener);, then why do the latter at all?

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JComponent;
import javax.swing.JFrame;

public class Scratch {

    public static void main(String[] args) {
        JFrame frame = new JFrame("Moving Rectangle");
        frame.setSize(500,500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        final MyComponent comp = new MyComponent(); 
        class MouseClickListener implements MouseListener {
            public void mousePressed(MouseEvent event) {}
            public void mouseReleased(MouseEvent event) {}
            public void mouseClicked(MouseEvent event) {
                int x = event.getX();
                int y = event.getY();
                comp.moveTo(x, y);
            }
            public void mouseEntered(MouseEvent event) {}
            public void mouseExited(MouseEvent event) {}
        }
        MouseListener listener = new MouseClickListener();
        comp.addMouseListener(listener);
        frame.add(comp);
        frame.setVisible(true);
    }
}

class MyComponent extends JComponent {

    private Rectangle box;
    public MyComponent() {
        box = new Rectangle(0,0,50,50);
    }
    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g; 
        g2.draw(box);
    }
    public void moveTo(int x, int y) {
        box.setLocation(x,y);
        repaint();
    }
}

asked 9 secs ago

Blood Brother

23

Associating a MouseListener with a JComponent