Button Allocation Help

Question

Hi all,
I am working on a java gui application that will have free-floating-button-boxes. In other words, there will be selections from a JFrame that will allow the user to select an option from a
frame that is not connected to the main application frame. Because
there are potentially several different button boxes that will change
as the functionality of the application is increased, I wanted to make
a generic frame that would dynamically allocate the button box based
upon an array of Strings input to the constructor. When I hard code the
string array, I have no problem constructing the box. (This is not the hard coded example ) but when I attempt to allocate and label the buttons "on the fly" I always get a null pointer exception thrown. I have tested the logic and I am not going off the end of the array (IllegalIndexException) but I cannot determine why this doesn't work.
I have cut the code down to what I believe is the minimum logic, without event handlers or other extraneous code and it is below along with the output and resultant exception. If anyone has an idea, I'd appreciate it.
Sincerely,
John
import javax.swing.*;
public class ButtonTest extends JFrame {
public ButtonTest( String[] args ){
init( args );
public void init( String[] args ){
JButton[] aButtonArray = new JButton[ args.length ];
getContentPane().setLayout( new java.awt.GridLayout( args.length , 1
for ( int i = 0; i < args.length; i++ ) {
aButtonArray[ i ].setLabel( args[ i ] );
getContentPane().add( aButtonArray[ i ] );
pack();
setSize( 100, 100 );
show();
public static void main( String[] args ){
String[] arr = new String[ args.length ];
for ( int i = 0; i < args.length; i++ ) {
arr[ i ] = args[ i ];
System.out.println( args[ i ] );
ButtonTest button = new ButtonTest( arr );
C:\Code_PlayGround\Java>java -cp . ButtonTest label1 label2 label3
label1
label2
label3
Exception in thread "main" java.lang.NullPointerException
at ButtonTest.init(ButtonTest.java:14)
at ButtonTest.<init>(ButtonTest.java:7)
at ButtonTest.main(ButtonTest.java:29)

Answer 1

You get a NPE because you've not populated the aButtonArray array.
for ( int i = 0; i < args.length; i++ ) {
  aButtonArray[ i ] = new JButton(args);
getContentPane().add( aButtonArray[ i ] );