Question

How do I get paintComponent to work within my drawArea JPanel? Additionally, my attempts to set the drawArea’s dimensions have failed. No drawing occurs once running, and the JPanel is minimal size. DOes this have to do with MigLayout?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import net.miginfocom.layout.*;
import net.miginfocom.swing.MigLayout;
import java.awt.geom.*;

public class OvalDrawer extends JApplet
{
private JLabel numberL;
private JTextField numberTF;

private NumHandler numHandler;

public static final int WIDTH = 500;
public static final int HEIGHT = 500;

public int number;

//Create Layout
public void init()
{
    setLayout(new MigLayout("wrap 2"));
    numberL = new JLabel("Enter number of ovals to draw:");
    numberTF = new JTextField(7);

    add(numberL);
    add(numberTF);

    numHandler = new NumHandler();
    numberTF.addActionListener(numHandler);

    JPanel drawArea = new JPanel();
    drawArea.setSize(400, 400);
    drawArea.setBorder(BorderFactory.createTitledBorder("Draw Area"));
    add(drawArea, "span 2");

    setSize(WIDTH, HEIGHT);
}

//Event Handler
public class NumHandler implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        number = Integer.parseInt(numberTF.getText());
        repaint();
    }

}

//Draw Ovals
public void paintComponent (Graphics g)
{
    super.paintComponents(g);
    int x = 10;
    int y = 10;
    int width = 200;
    int height = 100;

    for (int i = 0; i < number; i++)
    {
        g.drawOval(x, y, width, height);

        x += 5;
        y += 5;
        width += 5;
        height += 5;
    }
}
}

Answer 1

There is no paintComponent method in JApplet.

You should avoid painting directly onto a top level container like JApplet, its much more the just a single layer container.

Instead, create a second class, extending from something JPanel and perform you custom painting there.

UPDATED

You should also avoid using setPreferred/Minimum/MaximumSize, it’s to easy for some one else to circumvent.

public class OvalDrawer extends JApplet {

    private JLabel numberL;
    private JTextField numberTF;
    private NumHandler numHandler;
    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;
    public int number;

    //Create Layout
    public void init() {
//        setLayout(new MigLayout("wrap 2"));
        setLayout(new BorderLayout());
        numberL = new JLabel("Enter number of ovals to draw:");
        numberTF = new JTextField(7);

        JPanel header = new JPanel();
        header.add(numberL);
        header.add(numberTF);

        add(header, BorderLayout.NORTH);
        add(new PaintPane());

        numHandler = new NumHandler();
        numberTF.addActionListener(numHandler);

//        JPanel drawArea = new JPanel();
//        drawArea.setSize(400, 400);
//        drawArea.setBorder(BorderFactory.createTitledBorder("Draw Area"));
//        add(drawArea, "span 2");

        setSize(WIDTH, HEIGHT);
    }

    //Event Handler
    public class NumHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            number = Integer.parseInt(numberTF.getText());
            repaint();
        }
    }

    //Draw Ovals
    public class PaintPane extends JPanel {

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            int x = 10;
            int y = 10;
            int width = 200;
            int height = 100;

            for (int i = 0; i < number; i++) {
                g.drawOval(x, y, width, height);

                x += 5;
                y += 5;
                width += 5;
                height += 5;
            }
        }
    }
}