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Thanks KevinWorkman!!
Yes as I checked the b[0] is null. But why?? I create the buttons
" JButton b[] = new JButton[numberOfButtons];

b[i] = new JButton();
b[i].setEnabled(true);
...

this the error : Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
in this line : jPanel1.add(b[0]);
the line in blue

start is a button and bellow is it's actionPerformed...

in this line is the error :jPanel1.add(b[0]);
i want to put a button into jPanel1 ...when I use it outside the for there is no problem
Somehow there is a problem in the for loop

I get this Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
when i click the button Start, below is it's handler

Can't understand why...Please help me!!!!!!!!!!!!!!!!!
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