program not returning proper results for RadioButton

Question

When I run the code below, the first 2 buttons do not appear; however, the third one is visible in the frame.

public class RadioButton {
    RadioButton(){
        JFrame frame = new JFrame();
        JRadioButton button1 = new JRadioButton("One");
        button1.setBounds(50, 20, 50, 20);
        JRadioButton button2 = new JRadioButton("Two");
        button2.setBounds(50, 50, 50, 20);
        JRadioButton button3 = new JRadioButton("Three");
        button2.setBounds(50, 80, 50, 20);
        ButtonGroup bg  = new ButtonGroup();
        bg.add(button1);
        bg.add(button2);
        bg.add(button3);
        frame.add(button1);
        frame.add(button2);
        frame.add(button3);
        frame.setSize(300, 300);
        frame.setVisible(true);
        frame.setLayout(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new RadioButton();
    }

}

Answer 1

I guess since the OP set the layout manager to null, absolute positioning was what was wanted. This is not usually recommended. See the tutorial.

You need to re-order the code as follows - i.e set the layout before setting the bounds of the components.

public class RadioButton {

RadioButton() {
    JFrame frame = new JFrame();
    JRadioButton button1 = new JRadioButton("One");
    JRadioButton button2 = new JRadioButton("Two");
    JRadioButton button3 = new JRadioButton("Three");
    ButtonGroup bg = new ButtonGroup();
    frame.setLayout(null);
    bg.add(button1);
    bg.add(button2);
    bg.add(button3);
    frame.setSize(300, 300);
    frame.add(button1);
    frame.add(button2);
    frame.add(button3);
    button1.setBounds(50, 20, 80, 20);
    button2.setBounds(50, 50, 80, 20);
    button3.setBounds(50, 80, 80, 20);

    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            frame.setVisible(true);
        }
    });

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

public static void main(String[] args) {
    new RadioButton();
}
}

I am using OS X and I needed to make the buttons a bit bigger to avoid their captions being displayed as '...'. Finally I used invokeLater, which IIRC is best practice.

Answer 2

You need to set a layout manager for the container, I suggest you read the tutorial.

RadioButton(){
    JFrame frame = new JFrame();
    JRadioButton button1 = new JRadioButton("One");
    JRadioButton button2 = new JRadioButton("Two");
    JRadioButton button3 = new JRadioButton("Three");
    ButtonGroup bg  = new ButtonGroup();
    bg.add(button1);
    bg.add(button2);
    bg.add(button3);
    frame.getContentPane().setLayout(new FlowLayout());
    frame.add(button1);
    frame.add(button2);
    frame.add(button3);
    frame.setSize(300, 300);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

Answer 3

The default layout for JFrame is BorderLayout. Without specifying a region, each component you add is being placed into BorderLayout.CENTER. Since button3 was the last to be added, it replaced button2 (button2 replaced button1 when it was added). You could create a JPanel using FlowLayout, and add the three buttons there. Then add the JPanel to the JFrame.