Java

// This is an event that is supposed to clear the contents 
// of a third jTextField, if the first input box
// has a key typed in it:

private void jTextField1KeyTyped(java.awt.event.KeyEvent evt)
{                                     
   // Clear previous result in jTextField3,
   // if jTextField1 text is changed:

   arrJTxtFld[2].setText(""); // This is where the nullpointerexception occurs
}

// This is the code for the JTextField array:

private JTextField[] arrJTxtFld = {jTextField1, jTextField2, jTextField3};