CODEWITHSUNDEEP
javaswingnullpointerexceptioncardlayoutexcept
user3314100
user3314100

Reputation: 21

Throwing main:NullPointerException in using CardLayout

Here i am here trying to build simple CardLayout but it is throwing NullPointerException at line 19 and line 26. Here is the code. I am trying to show only the firstpanel named panel1 from the given 2 panel which are added indirectly into main controlPanel. I am beginner to Java Swing GUI Programming. PLease help me to solve this problem.

import java.awt.*;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.CardLayout;
import java.awt.event.*;
import javax.swing.*;

public class test {

   private JFrame mainFrame;
   private JLabel label1 = new JLabel("This is Label 1");
   private JLabel label2 = new JLabel("This is Label 2");
   private JPanel controlPanel;
   private JPanel panel1;
   private JPanel panel2;

   public static void main(String[] args){
      test  coutex = new test();      
      coutex.prepareGUI();  
   }

   public void prepareGUI(){
      mainFrame = new JFrame("Java Swing Examples");
      mainFrame.setSize(400,400);
      CardLayout cout = new CardLayout();
      controlPanel.setLayout(cout);
      panel1.add(label1);
      panel2.add(label2);
      panel1.setBackground(Color.BLUE);
      panel2.setBackground(Color.RED);
      controlPanel.add(panel1,"1");
      controlPanel.add(panel2,"2");
      cout.show(controlPanel,"1");
      mainFrame.add(controlPanel);
      mainFrame.setVisible(true);  
      mainFrame.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent windowEvent){
            System.exit(0);
         }        
      });
   }
}

Upvotes: 1

Views: 164

Answers (3)

newuser
newuser

Reputation: 8466

Not initialize but trying to assign the following things

private JPanel controlPanel = new jpanel();
private JPanel panel1 = new jpanel();
private JPanel panel2 = new jpanel();

instead of 

private JPanel controlPanel;
private JPanel panel1;
private JPanel panel2;

Upvotes: 0

Kavindu Dodanduwa
Kavindu Dodanduwa

Reputation: 13069

At line 13 , you don't initialize ControlPanel 

private JPanel controlPanel;

Upvotes: 0

Alexis King
Alexis King

Reputation: 43872

The issue is here:

controlPanel.setLayout(cout);

The controlPanel object is never initialized, so you're trying to call a method on a null object. Set it to a new JPanel() first.

Furthermore, you never initialize panel1 or panel2. The same advice applies.

Upvotes: 2

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