Java - JComponent paintComponent()

Question

I am trying to figure out how to repaint() a class that extends the JComponent . I want to have each class extend JComponent and then supply its own paintComponent() . ( super.paintComponent() . This way I can make a circle class or whatever class that I want to make and then I can repaint() it when ever I want to as long as it is added to the JPanel that goes in the JFrame . Below are all of the code that are needed to run.

Class 1:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;

public class DDHGenericFrame extends JFrame {

    private static final long serialVersionUID = 1L;

    /* User defined class that is below */
    DDHGenericPanel d = new DDHGenericPanel(); 

    public DDHGenericFrame() {
        initUI();
    }

    public final void initUI() {
        add(d);
        setSize(650, 350);
        setTitle("Lines");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        DDHGenericFrame ex = new DDHGenericFrame();
        ex.setVisible(true);
    }
}

Class 2:

import java.awt.Graphics;
import javax.swing.JPanel;

class DDHGenericPanel extends JPanel {
    private static final long serialVersionUID = 1L;

    DDHGenericPanel() {
        System.out.println("DDH Generic JPanel");
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        //paint code goes here of whatever
    }
}

Class 3:

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;

public class DDHCircleOne extends JComponent {
    private static final long serialVersionUID = 1L;

    int counter = 0;

    public DDHCircleOne() {
        counter++;
        System.out.println("DDHCircle Constructor");
    }

    public void paintComponent(Graphics g2) {
        super.paintComponent(g2);
        Graphics2D c2D = (Graphics2D) g2;
        c2D.setColor(Color.yellow);
        c2D.fillRect(0, 0, getSize().width, getSize().height);
        if (counter % 2 == 2) {
            System.out.println("RED");
            counter++;
            c2D.setColor(Color.red);
            c2D.fillRect(0, 0, getSize().width, getSize().height);
        } else {
            System.out.println("BLUE");
            counter++;
            c2D.setColor(Color.blue);
            c2D.fillRect(0, 0, getSize().width, getSize().height);
        }
    }
}

The above three classes are what I have in my package. I want DDHCircleOne to be able to repaint it self whenever an instance of it is created and calls the method repaint() . This way I can just make a class that extends JComponent and then override the paintComponent() and then call repaint() .

If I had a button that said repaint in red and another button that says repaint in blue the circle or whatever I had in the frame will repaint itself when the variableName.repaint() is called.

doughauf@outlook.com

Answer 1

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    repaint();
}

Never invoke repaint() in a painting method. This will cause an infinite loop.

There is no need for you generic panel. You can add a component to any panel.

If you want the color of the circle to change, then you need to change a property of your component. For example you can just use the setForeground(...) method to change the color:

//c2D.setColor(Color.red);
c2D.setColor( getForeground() );

So when you click on your button you just invoke circle.setForeground(Color.RED);

The setForeground() method of JComponent will invoke the repaint() method on the component for you.