Null pointer exception Radiobuttons

[Harshit R Shah]

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class ChoiceAction 
{
    Choice c,c1,c2,c3,c4;
    Label intro,l,l1,l2,l3,l4;
    Label ll,l11,l22,l33,l44;
    JRadioButton b0,b5,b10,b20;
    public ChoiceAction()
    {
        JFrame frame = new JFrame("BILL");
        JPanel panel = new JPanel();

        frame.setTitle("BILL");
        frame.setSize(400,400);
        frame.setLayout(new FlowLayout());
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Create choice
        c=new Choice();
        c1=new Choice();
        c2=new Choice();
        c3=new Choice();
        c4=new Choice();

        // Add items
        c.add("--");
        c.add("Crocin");
        c.add("Hifen");
        c.add("Neurobion");
        c.add("Urimax");
        c.add("Pantocid DSR");

        c1.add("--");
        c1.add("Acuflam");
        c1.add("O2h");
        c1.add("Cifran OZ");
        c1.add("Rantec D");
        c1.add("Cetzine");

        c2.add("--");
        c2.add("Eltroxin");
        c2.add("Becosule");
        c2.add("Combiflam");
        c2.add("Lomotil");
        c2.add("Vikoryl");

        c3.add("--");
        c3.add("Alzolam");
        c3.add("Sporidex");
        c3.add("Flexon");
        c3.add("Droxyl");
        c3.add("Enzoflam");

        c4.add("--");
        c4.add("Hopace H");
        c4.add("Ecosprin");
        c4.add("Vertin");
        c4.add("Imdur");
        c4.add("Storvas");

        // Add choice
        panel.add(c);
        panel.add(b0);
        panel.add(b5);
        panel.add(b10);
        panel.add(b20);
        b0.setSelected(true);

        panel.add(c1);
        panel.add(b0);
        panel.add(b5);
        panel.add(b10);
        panel.add(b20);
        b0.setSelected(true);

        panel.add(c2);
        panel.add(b0);
        panel.add(b5);
        panel.add(b10);
        panel.add(b20);
        b0.setSelected(true);

        panel.add(c3);
        panel.add(b0);
        panel.add(b5);
        panel.add(b10);
        panel.add(b20);
        b0.setSelected(true);

        panel.add(c4);
        panel.add(b0);
        panel.add(b5);
        panel.add(b10);
        panel.add(b20);
        b0.setSelected(true);
        // Create label
        intro = new Label();
        l=new Label();
        l1=new Label();
        l2=new Label();
        l3=new Label();
        l4=new Label();
        // giving write - up
        intro.setText("BILL OF ");
        // Create Radio Button
        ButtonGroup buttonGroup = new ButtonGroup();
        b0 = new JRadioButton("No order");
        b5 = new JRadioButton("5 Capsule");
        b10 = new JRadioButton("10 Capsule");
        b20 = new JRadioButton("20 Capsule");
        buttonGroup.add(b0);
        buttonGroup.add(b5);
        buttonGroup.add(b10);
        buttonGroup.add(b20);

        // Add label
        panel.add(l);

        frame.add(panel);

        // Add item listener
        c.addItemListener(new ItemListener(){
                public void itemStateChanged(ItemEvent ie)
                {
                    l.setText("You selected "+c.getSelectedItem());
                }
            });

    }

    public static void main()
    {
        new ChoiceAction();
    }
}

==============

java.lang.NullPointerException
	at java.awt.Container.addImpl(Container.java:1090)
	at java.awt.Container.add(Container.java:410)
	at ChoiceAction.<init>(ChoiceAction.java:67)
	at ChoiceAction.main(ChoiceAction.java:137)

Any ideas where I went wrong ?

[m Korbel]

there I see four potential issues

- use Swing JComponent rather than AWT (Choice and Label), don't to mix AWT with Swing

- you forgot to intialize JRadioButton b0,b5,b10,b20;

- main class isn't proper ( something - public static void main(String[] args) { )

- read Oracle tutorial Initial Thread

[Harshit R Shah]

m Korbel wrote:there I see four potential issues

- use Swing JComponent rather than AWT (Choice and Label), don't to mix AWT with Swing

- you forgot to intialize JRadioButton b0,b5,b10,b20;

- main class isn't proper ( something - public static void main(String[] args) { )

- read Oracle tutorial Initial Thread

Can you tell me how to initialize the buttons.I am in a fix and am totally new to AWT/swing programs

[Nam Ha Minh]

Harshitsss Shah wrote:
Can you tell me how to initialize the buttons.I am in a fix and am totally new to AWT/swing programs

Using JRadionButtons is pretty simple. Here I googled for you:

- From the Java tutorial: How to Use Buttons, Check Boxes, and Radio Buttons

- From the web: JRadioButton basic tutorial and examples

Hope that helps.

[Campbell Ritchie]

Harshitsss Shah wrote: . . . Can you tell me how to initialize the buttons. . . .

Same way you initialise any other references. Preferably in the constructor.

Don't try to squeeze so many declarations into one line, and leave some spaces. I doubt whether those buttons need to be fields'; they can probaboy be local variables in the constructor/initGUI method.

[K. Tsang]

Lines 65-99 should be after all those other create statements. You add the buttons to the panel last just before adding the panel to the frame.