import javax.swing.SwingUtilities;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.BorderFactory;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseMotionListener;
import java.awt.event.MouseMotionAdapter;

public class SwingPaintDemo3 {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI() {
        System.out.println("Created GUI on EDT? "
                + SwingUtilities.isEventDispatchThread());
        JFrame f = new JFrame("Swing Paint Demo");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new MyPanel());
        f.pack();
        f.setVisible(true);
    }
}

class MyPanel extends JPanel {

    private int squareX = 50;
    private int squareY = 50;
    private int squareW = 20;
    private int squareH = 20;

    public MyPanel() {

        setBorder(BorderFactory.createLineBorder(Color.black));

        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                moveSquare(e.getX(), e.getY());
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            public void mouseDragged(MouseEvent e) {
                moveSquare(e.getX(), e.getY());
            }
        });

    }

    private void moveSquare(int x, int y) {
        int OFFSET = 1;
        if ((squareX != x) || (squareY != y)) {
            repaint(squareX, squareY, squareW + OFFSET, squareH + OFFSET);
            squareX = x;
            squareY = y;
            repaint(squareX, squareY, squareW + OFFSET, squareH + OFFSET);
        } 
    }

    public Dimension getPreferredSize() {
        return new Dimension(250, 200);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        g.drawString("This is my custom Panel!", 10, 20);
        g.setColor(Color.RED);
        g.fillRect(squareX, squareY, squareW, squareH);
        g.setColor(Color.BLACK);
        g.drawRect(squareX, squareY, squareW, squareH);
    }
}