getting a null pointer when trying to create a new font

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Justin - 12 Oct 2006 00:07 GMT

I have a class that extends a JDialog component. Within the
constructor, I call an addWidgets method. That method contains the
line in question:

Font nameFont = getFont().deriveFont(1,30);

This line is causing a null pointer exception. I dont understand why,
if someone could help me create the new font and explain to me why this
causes an error, it would be greatly appreciated.

Also the import list is as follows:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.font.*;

Thanks

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Thomas Weidenfeller - 12 Oct 2006 08:13 GMT

> I have a class that extends a JDialog component. Within the
> constructor, I call an addWidgets method. That method contains the
[quoted text clipped - 3 lines]
>
> This line is causing a null pointer exception. I dont understand why,

A component which hasn't been realized does this. It's the way AWT and
Swing work.

/Thomas

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Justin - 12 Oct 2006 16:00 GMT

Ok, but did I not initialize it on the line:

Font nameFont = getFont().deriveFont(1,30);

???

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Tor Iver Wilhelmsen - 12 Oct 2006 18:40 GMT

> Ok, but did I not initialize it on the line:
>
> Font nameFont = getFont().deriveFont(1,30);

getFont() requires a native peer, and that won't exist until the
component has been shown.

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Joe Attardi - 12 Oct 2006 18:46 GMT

> > Ok, but did I not initialize it on the line:
>
> > Font nameFont = getFont().deriveFont(1,30);getFont() requires a native peer, and that won't exist until the
> component has been shown.

Justin,
This is why code like that can be troublesome. If getFont() returns
null, as it is in this case, in your code there's no way to stop the
call to deriveFont(1, 30) and thus your NullPointerException.

While more verbose, something like this is a little more
error-friendly:

Font nameFont = getFont();
if (nameFont != null)
nameFont = nameFont.deriveFont(1, 30);

The burden is on you to then provide graceful handling of this error
condition, but at least your user won't see a NullPointerException...

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Joe Attardi
jattardi@gmail.com

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getting a null pointer when trying to create a new font

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