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Intelliji Hallo World sample program error

Intelliji Hallo World sample program error

Intelliji Hallo World sample program error

I am new to Java and I am writing a simple prg to display msg in intelliji; The code and error is as below. Please advise. thanks.

public class Main {

public static void main(String[] args) {


JFrame frame = new JFrame("App");
frame.setContentPane(new App().panelMain);




package sample;

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class App {
public JButton buttonMsg;
public JPanel panelMain;

public App() {
buttonMsg.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog(null,"HALLO WORLD");

private void createUIComponents() {
// TODO: place custom component creation code here


The Error msg is:

Hallo World
Exception in thread "main" java.lang.NullPointerException
at sample.App.$$$setupUI$$$(App.java)
at sample.App.<init>(App.java:12)------ buttonMsg.addActionListener(new ActionListener() {
at sample.Main.main(Main.java:53)----------frame.setContentPane(new App().panelMain);

Process finished with exit code 1

RE: Intelliji Hallo World sample program error

In Java, objects need to be created, primitive types don't. For instance


// This will work
int x;
x = 20;

// This won't work
JButton noworkies;

// It needs to be created first
JButton workies = new JButton(...);  // No idea what the creation params are

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