使用Swing影响鼠标事件的布尔变量

Question

I am not sure why the mouse events set by my mouse listener are not affecting whether or not the hat is drawn. The variable "mouseInside" seems not to be affected by the mouse events. How do I change the variable to false with the mouse events?

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.geom.*;

public class EyesOpen extends JPanel{

    private Ellipse2D.Double head;
    private Ellipse2D.Double eyeOne;
    private Ellipse2D.Double eyeTwo;
    private Rectangle2D.Double hatBody;
    boolean mouseInside;



    public EyesOpen(){

        this.setFocusable(true);
        this.requestFocus();
        this.setPreferredSize(new Dimension(500,500));

        head = new Ellipse2D.Double(180,180,140,140);
        eyeOne = new Ellipse2D.Double(220,220,20,20);
        eyeTwo = new Ellipse2D.Double(260,220,20,20);
        hatBody = new Rectangle2D.Double(170,180,160,20);



    class MyMouseListener implements MouseListener{
        public void mouseClicked(MouseEvent e) { 
       }
        public void mouseEntered(MouseEvent e){

           mouseInside=true;

        }
        public void mouseExited(MouseEvent e){
             mouseInside=false;


        }
        public void mousePressed(MouseEvent e){

        }
        public void mouseReleased(MouseEvent e){
        }
}
this.addMouseListener(new MyMouseListener());    
}

    public void paintComponent(Graphics g){

        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;

        g2.setPaint(Color.BLUE);
        g2.fill(head);

        g2.setPaint(Color.BLACK);
        g2.fill(eyeOne);

        g2.setPaint(Color.BLACK);
        g2.fill(eyeTwo);

        if(mouseInside=true){
        g2.setPaint(Color.BLACK);
        g2.fill(hatBody);}

    }

public static void main(String[] args){
    JFrame f = new JFrame("Head");

    f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    f.setLayout(new FlowLayout());
    f.add(new EyesOpen());
    f.pack();
    f.setVisible(true);
    }
}

Answer 1

Don't forget to call repaint() after changing the boolean.

To be precise, you could specify that it is the drawing component's method that gets called via EyesOpen.this.repaint(); , but this isn't absolutely necessary in this current program (I don't think).

Other nitpicks:

• The paintComponent(...) method should be specified as protected not public . No sense in exposing it any more than it needs to be exposed.
• Don't forget to use the @Override annotation any time that you think that you're overriding a method. While it may not matter with this program, it will save your behind in the future.
• You will want to start your GUI on the Swing thread in your main method by placing your JFrame creation code inside of a Runnable and then queuing that Runnable onto the event queue by placing it into a SwingUtilities.invokeLater(/** Your Runnable Goes Here **/);