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Editorial Team
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Asked: 2026-05-18T07:06:31+00:00

private final Button[] BUTTONS = { btn1, btn2, btn3,btn4 }; … btn1 = (Button)

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private final Button[] BUTTONS = {
    btn1, btn2, btn3,btn4
};

...

btn1 = (Button) this.findViewById(R.id.btn_1);
btn2 = (Button) this.findViewById(R.id.btn_2);
btn3 = (Button) this.findViewById(R.id.btn_3);
btn4 = (Button) this.findViewById(R.id.btn_4);

...

int n = BUTTONS.length;
for(int i=0; i<n; i++) {
    if(DEBUG) Log.d(TAG, String.valueOf(i));
    BUTTONS[i].setOnClickListener(this);
}

throws NullPointerException, whereas

btn1.setOnClickListener(this);
btn2.setOnClickListener(this);
btn3.setOnClickListener(this);
btn4.setOnClickListener(this);

works fine. Doesn’t make any sense to me.

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1 Answer

  1. Editorial Team

    I think it’s because your Buttons array is created when btn1,… are still null.

    So when you call BUTTONS[i].setOnClickListener in the loop you are really saying null.setOnClickListener which will give an exception.

    Try setting up the array as a variable and sey AFTER you’ve assigned btn1, etc.

    Haven’t tested it but something like this might work better…

    private ArrayList mBtns = new ArrayList();

    private void initButton(int id) {
    button = (Button) findViewById(id);
    button.setOnClickListener(this);
    mBtns.add(button);
    }

    …

    initButton(R.id.btn_1);
    initButton(R.id.btn_2);
    initButton(R.id.btn_3);
    initButton(R.id.btn_4);

    Also unless the buttons do very similar things you may find it better to simply define the onClick attribute on each in the layout and save yourself A LOT of coding (only available in Android 1.6 and higher).

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