Override setText() method in JLabel

Question

I have the following code implemented in Java.

public class FadeLabel extends javax.swing.JLabel {

    private Timer onTimer;

    public FadeLabel() {
        init();
    }

    private void init(){
        setHorizontalAlignment(CENTER);
        setVerticalAlignment(CENTER);
        onTimer = new Timer(100, (ActionEvent e) -> {
            // animation code
        });
    }

    @Override
    public void setText(String text) {
        onTimer.start();
        super.setText(text);
    }
}

When I create an object of this class, it gives a NullPointerException in the setText() method, the line onTimer.start().

I want to know why is this exception happening..?

ps: I know what is a NullPointerException is. I want to know how is it generated here..

This is how I instantiate.

notificationLabel = new FadeLabel();

You are creating the Label with `new FadeLabel()` ? If you use any other constructor, you would not create a new Timer. That is the only one I could think of right now. — geisterfurz007, Oct 12 '17 at 07:53
@geisterfurz007 since there is no other constructor, let's assume he's not using another one — Stultuske, Oct 12 '17 at 07:55
Show us the code piece where you are actually creating new instance `FabeLabel` — Antoniossss, Oct 12 '17 at 07:55
Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — TT., Oct 12 '17 at 07:59
@TT. nope. it's not a duplicate of that. he's asking why the NPE, when the variable is in fact instantiated — Stultuske, Oct 12 '17 at 08:00
What are the odds that NPE comes actually not from `onTimer.start()` but from null reference to `FadeLabel` like this: `FadeLabel label; label.setText()` ?? :) — Antoniossss, Oct 12 '17 at 08:00
Please add whole stacktrace as I suspect that NPE is not comming from the line you have pointed out. — Antoniossss, Oct 12 '17 at 08:00
@Antoniossss not, since then the NPE would not be thrown in the setText method — Stultuske, Oct 12 '17 at 08:01
@Stultuske Im saying that OP is mistaken and NPE is not from the line he pointed out. Stacktrace needed. — Antoniossss, Oct 12 '17 at 08:02
@Antoniossss he COULD be mistaken. bit of a difference there. — Stultuske, Oct 12 '17 at 08:05

score 8 · Accepted Answer · answered Oct 12 '17 at 08:05

8

Looking at the source code for JLabel

public JLabel() {
    this("", null, LEADING);
}

public JLabel(String text, Icon icon, int horizontalAlignment) {
    setText(text);
    setIcon(icon);
    setHorizontalAlignment(horizontalAlignment);
    updateUI();
    setAlignmentX(LEFT_ALIGNMENT);
}

Thus we can see that the no-argument constructor calls the other one, which then calls setText. However at that point your init method hasn't run, so onTimer is still NULL.

answered Oct 12 '17 at 08:05

Buddy

10,874
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2

This is then a good illustration why calling non-final methods in a constructor is an anti-pattern... – Gyro Gearless Oct 12 '17 at 08:07
2

This is why netbeans gives warning when calling an overridable methods in the constructor.. – Ramesh-X Oct 12 '17 at 08:23

score -3 · Answer 2 · edited Oct 12 '17 at 07:59

-3

You define the property onTimer. You have a method init. You must call it to instantiate the timer property onTimer.

edited Oct 12 '17 at 07:59

Buddy

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answered Oct 12 '17 at 07:56

michaeldbjava

114
10

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According to the code shown he is doing that during no-args construction. – Antoniossss Oct 12 '17 at 07:57
Thanks for your comment. – michaeldbjava Oct 12 '17 at 08:01

Override setText() method in JLabel

2 Answers2