How to Draw some shape on JPanel using ActionListener?

Question

I\'m practising to draw a shape on a JPanel by clicking on a Jbutton, but I cannot. It\'s been five hours that I\'m surfing the web, but I cannot find the way to do it. Thi

Answer 1

Here is a derived example from your code.

As @MadProgrammer said, don't extend JFrame.

In the following example, here are the major changes :

• give a non-null value to botSelected, or the first calls to paintComponent will give you a NullPointerException

• the class now extends JPanel, and overrides paintComponent for custom painting

• the ActionListener is an anonymous class, because you don't need a separate class, and it has direct access to the fields from Shape

• botSelected is no longer static (see above point)

.

import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

class Shape extends JPanel {
    JButton rec, circle;
    String botSelected = "";// don't let it be null, it would make paintComponent crash on startup

    Shape() {
        frameSet();
    }

    void frameSet() {
        JFrame frame = new JFrame();
        frame.setVisible(true);
        frame.setSize(600, 300);
        rec = new JButton("Rectangle");
        circle = new JButton("Circle");

        frame.add(this);
        this.add(rec);
        this.add(circle);
        // anonymous class, has access to fields from the outer class Shape
        ActionListener clk = new ActionListener() {
            public void actionPerformed(final ActionEvent e) {
                botSelected = e.getActionCommand();
                repaint();
            }

        };
        rec.addActionListener(clk);
        circle.addActionListener(clk);
    }

    //custom painting of the JPanel
    @Override
    public void paintComponent(final Graphics g) {

        super.paintComponent(g);
        if (botSelected.equals("Rectangle")) {
            g.fillRect(50, 50, 50, 50);
        } else if (botSelected.equals("Circle")) {
            g.fillOval(50, 50, 50, 50);
        }
    }

    public static void main(final String[] arg) {
        Shape s = new Shape();
    }

}