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The purpose of using getContentPane()

Griff Haldeman
Greenhorn

Joined: Jul 01, 2011
Posts: 5
What's the point of calling frame.getContentPane().add(button) when frame.add(button) works all the same? To my understanding, adding directly to the frame without first getting the content pane is disparaged, but if someone could elaborate on this, it'd be great.
Greg Charles
Sheriff

Joined: Oct 01, 2001
Posts: 2840
    
  11

It's been awhile since I used Swing, but if I remember right, JFrame has an addImpl() method that adds components to the content pane by default. That's why frame.getContentPane.add(...) does the same thing as frame.add(...). As to why or if that's a bad practice, I'm not sure. Probably because you're not being explicit about what you're doing. There's a glass pane, where you can draw things that appear superimposed over what's in the content pane. Also a root pane and layered pane, but I forget what those do.
Griff Haldeman
Greenhorn

Joined: Jul 01, 2011
Posts: 5
Thanks, just what I wanted to know.
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19655
    
  18

In Java 1.4 and before, adding components to a JFrame directly, or setting its layout directly, would result in an error (of java.lang.Error or some sub class, can't remember which one it was). You really needed to use the content pane. In Java 5.0 they decided it made more sense to just redirect those calls to the content pane.


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It is sorta covered in the JavaRanch Style Guide.
 
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