Codename one giving java NullPointerException error when creating dynamic buttons from an array loop

Question

I am trying to create buttons dynamically in a loop from an array. I keep getting java NullPointerException error even after I read and followed the instructions on this post where someone had a similar problem and was advised to allocate the elements within his array. I did that but am still getting the same error. Can someone please show me where am going wrong? Here is my code:

@Override
protected void onMain_SavePersonAction(final Component c, ActionEvent event) {

    // declares an array of integers
    final String[] anArray;

    // allocates memory for 8 values
  anArray = new String[]{"100","200","400","500","600","700","800","900"};      

    Button[] button = new Button[anArray.length];
    for (int i = 0; i < anArray.length; i++) {
        button[i].setIcon(fetchResourceFile().getImage("personIcon.png"));
        button[i].setText("Member: "+i);
        button[i].addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {

            findName().setText("Firstname ");
            findVorname().setText("Secondname ");
            findFamMname().setText("Firstname Secondname" );
            findFamMname().setIcon(fetchResourceFile().getImage("personIcon.png"));
            findFamMname2().setText("Firstname Secondname ");
            findFamMname2().setIcon(fetchResourceFile().getImage("personIcon.png"));
            findDeleteMember().setVisible(true);

            c.getComponentForm().revalidate();
            c.getComponentForm().repaint();

           }
        });
        findFamilyMembers().addComponent(button[i]);

     }

    c.getComponentForm().revalidate();
    c.getComponentForm().repaint();

}

button[i].setIcon(fetchResourceFile().getImage("personIcon.png")); when I comment it out then the line after that does the same,so its all the lines with button[i]. — Caleb Nasio
– Caleb Nasio, Commented Sep 29, 2014 at 6:51

Hovercraft Full Of Eels · Accepted Answer · 2014-09-29 00:46:44Z

You're using items in your Button[] array before creating any items and putting them in the array. Think of an array of objects similar to an empty egg carton. You can't make an omelettes using the egg carton, until you first fill it with eggs!

Change this:

for (int i = 0; i < anArray.length; i++) {
    button[i].setIcon(fetchResourceFile().getImage("personIcon.png"));

to this:

for (int i = 0; i < anArray.length; i++) {
    button[i] = new Button(); // you need to first create and assign a button object!
    button[i].setIcon(fetchResourceFile().getImage("personIcon.png"));

More importantly, you need to learn the general concepts of how to debug a NPE (NullPointerException). You should inspect the line carefully that throws the exception, find out which variable is null, and then trace back into your code to see why. You will run into these again and again, trust me.

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