How I can move a shape on mouse move in java

Question

I have this code, it creates a simple smily face. I want to move the eyes of the face with mouse movement. Here is the code

int a,b;
public void recieve(int x,int y)
{
    a=x;
    b=y;
    System.out.println("xaxis"+a+"yaxis"+b);
}

@Override
public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    System.out.println("x axis: "+a+" -- y axis: "+b);
    g.drawArc(100, 50, 150, 150, 0, 360);
    g.drawArc(125, 65, 40, 40, 0, 360);
    g.drawArc(180, 65, 40, 40, 0, 360);
    g.drawArc(165, 105, 15, 15, 60, 180);


    g.fillOval(a-130, 70, 15, 15);
    g.fillOval(b-185, 70, 15, 15);
}

Answer 1

You need to implement MouseMotionListener and attach it to whatever JPanel subclass your paintComponent() method is from. Within its methods, modify the values of your 'a' and 'b' variables.

Below is an example. It wasn't clear to me from your question what type of movement you want the eyes to do - e.g. whether the pupils should always be 'looking at' the mouse pointer without leaving the eyes - as subtracting the starting value of x from the x-coordinate of the mouse pointer for the left eye and the starting value of x from the y-coordinate of the mouse pointer for the right eye as your code snippet suggests doesn't really produce a meaningful result.

In the demo below, therefore, the eyes just trail the mouse pointer. It shows you how to pick up the mouse movement event and get the X and Y coords of the mouse - how you use these to adjust the position of the pupils in whatever way you are looking for is up to you, and is (hopefully) now just a mathematical question.

import javax.swing.SwingUtilities;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

public class MouseTrackingSmilieFace extends JFrame {

    private int a;
    private int b;

    private JPanel smilieFacePanel = new JPanel() {
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawArc(100, 50, 150, 150, 0, 360);
            g.drawArc(125, 65, 40, 40, 0, 360);
            g.drawArc(180, 65, 40, 40, 0, 360);
            g.drawArc(165, 105, 15, 15, 60, 180);
            g.fillOval(a, b, 15, 15);
            g.fillOval(a+55, b, 15, 15);
            // Register the motion listener
            addMouseMotionListener(new MouseMotionListener() {

                // Do the same thing whether the mouse button is depressed...
                public void mouseDragged(MouseEvent e) {
                    processMovement(e);
                }

                // ... or not.
                public void mouseMoved(MouseEvent e) {
                    processMovement(e);
                }

                /* Process the movement by capturing the x coordinate of the mouse in member variable 'a'
                 * and the y coordinate in member variable 'b'.
                 */
                private void processMovement(MouseEvent e) {
                    a = e.getX();
                    b = e.getY();
                    System.out.println("X = " + a + " Y = " + b);
                    smilieFacePanel.repaint();
                }
            });
        }
    };

    private MouseTrackingSmilieFace() {
        // Invoke the JFrame superclass constructor and configure the frame
        super("Mouse-tracking smilie face");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(400,400);
        this.setVisible(true);
        // Add a panel to the frame and draw the face within it.
        this.add(smilieFacePanel);
    }

    public static void main(String[] args) {
        // Create on the Event Dispatch Thread.
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new MouseTrackingSmilieFace();
            }
        });
    }
}