Question

I’m trying to learn how to do the GUI stuff in java with coding style
and this is what I’ve written :

import java.awt.Container;
import java.awt.Panel;

import javax.swing.*;

public class Class1 extends JFrame {


    public void createGUI()
    {
        JpanelMock jm = new JpanelMock();
        setTitle("Frame1");
        setSize(320,200);
        this.add(jm.drawGUI());

    }

    public static void main(String [] arg)
    {
        Class1 cls = new Class1();

        cls.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        cls.setVisible(true);
        cls.createGUI();
    }

}

//----------------------------JpanelMock.java


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

public class JpanelMock extends JPanel {

    public JpanelMock() {

    }

    public Component drawGUI()
    {
        super.setBackground(Color.YELLOW);
        JButton b = new JButton("button 1");
        JLabel l = new JLabel("label 1");
        JTextField tf = new JTextField("text 1");
        this.add(b);
        this.add(l);
        this.add(tf);
        return this;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        //drawGUI();
    }

}

but when I start the program if I don’t do anything related to redrawing event I can’t see my yellow jpanel with a text + button in it.
why is this happening?

Answer 1

Whenever I see a question such as yours, I don’t have to look at the code. You’re calling setVisible(true) on the JFrame before adding components to it. Change the order of this: call setVisible(true) on your JFrame only after all components have been added.

e.g.,

public static void main(String [] arg) {
    Class1 cls = new Class1();

    cls.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    // cls.setVisible(true); // *** removed
    cls.createGUI();
    cls.setVisible(true); // *** added
}