Paint method in a class, on a Jpanel, design mode at Netbeans

Question

I've been trying to program an applet with Netbeans able to draw some graphics into a jPanel, as you can see: ![enter image description here][1]

Applet form:

package Experimento2;

import javax.swing.*;
import java.awt.*;


public class Experimento2 extends javax.swing.JApplet {


    public void init() {
        try {
            java.awt.EventQueue.invokeAndWait(new Runnable() {
                public void run() {
                    initComponents();
                } 
            });
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }


    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        //ZonaGrafica zg = new ZonaGrafica();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 466, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 259, Short.MAX_VALUE)
        );

        jButton1.setText("jButton1");

        jButton2.setText("jButton2");

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addGap(27, 27, 27)
                .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 175, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 54, Short.MAX_VALUE)
                .addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 187, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(23, 23, 23))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(85, 85, 85)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 61, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 61, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(37, 37, 37))
        );

        //jPanel1.add(zg,BorderLayout.CENTER);
        //zg.repaint();
    }// </editor-fold>


    // Variables declaration - do not modify
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JPanel jPanel1;
    // End of variables declaration

}

And the ZonaGrafica class, which is in the same package:

package Experimento2;

import javax.swing.JApplet;
import java.awt.*;

public class ZonaGrafica extends JApplet{

    @Override
    public void paint(Graphics g) {
        super.paint(g);

        g.setColor(Color.red);
        g.fillOval(45, 65, 34, 54);
        g.fillOval(45, 120, 34, 54);
        g.fillOval(45, 180, 34, 54);
    }
}

But unfortunately, nothing happens when I run the jApplet form. In the place where the paint method is supposed to draw some red ovals, nothing is shown. I have no clue to solve this issue, and I would be grateful to whom could help me to solve it..

Answer 1

Don't override paint. Try with paintComponent instead.

Your ZonaGrafica object is never instantiated(commented). I hope you are at least doing that.

In addition to that, you are trying to ad a JApplet (ZonaGrafica) to another JApplet (Experimento2). Refactor ZonaGrafica and let it extend JPanel or JLabel.

Answer 2

The form editor “would” work with either overriden paint or paintComponent , though Heisenbug's suggestion to make it paintComponent is still a good one.

From reading your code I think that you simply hit the “customise code” button added a few lines and thought that would sort it. It doesn't, because:

1. GroupLayout doesn't work that way. It is not at all kind to the someContainer.add() approach of adding UI.
2. Speaking of which, the Border layout constant makes no sense.
3. And at design time the code isn't even run, anyway. The form editor uses an XML document to track what components to instantiate and how, so you wouldn't see your custom paint logic even if you did something like adding a JPanel and customising the constructor to read eg jPanel3 = new ZonaGrafica(); . Which brings me to:
4. The only way to make the component show up properly at design time is to have it compiled first, then added to the form through the “Add Java Bean” feature of the editor. If your code subclasses JPanel it will behave as a JPanel in the form editor, if it subclasses a JButton it would behave like a JButton and so on... This also removes the need for any quick hacks in the “customise code” part of the editor.

So to sum up: (1) compile your code, (2) then add the ZoneGrafica using the “Add Java Bean” function. You will need to know its fully qualified classname (eg com.foo.ZonaGrafica ) for that.