Extends JFrame vs. creating it inside the program

Question

When making an application using Swing, I\'ve seen people do one of the two things to create a JFrame. Which is a better approach and why?

I\'m a beginner at Java an

Answer 1

Prefer composition over inheritance.

The 2nd example uses inheritance, but for no good reason, since it does not change the functionality of JFrame.

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As an aside, if those are examples of code you are seeing, find a new source^{1 supplementary}. Even in the few code lines shown, each does highly questionable things. E.G.

1. Neither GUI is created on the Event Dispatch Thread.
2. getContentPane().setBackground(Color.WHITE); getContentPane().setLayout(null); setSize(800, 600);
   • The first part of the 1st line (getContentPane()) has not been necessary since Java 1.5
   • The second line uses a null layout, which will break in more ways I can count or describe.
   • The third line should best be replaced with pack();
3. JFrame guiFrame = new JFrame(); guiFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); guiFrame.setTitle("Example GUI"); guiFrame.setSize(300,250);
   • The first and 3rd lines could be contracted to:
     JFrame guiFrame = new JFrame("Example GUI");
   • The 2nd line is better set to guiFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
   • The 3rd line again sets a size to the frame.

Supplement

1. Having mentioned you do search SO, here is a tip. Check out the posts of the top 15 providers of answers in the Swing top users. Whatever advice/code you glean from these people, would commit few if any of the mistakes in those code samples.
   
   Some don't often (or ever) provide self contained examples like a few of us commonly do (and don't look to those examples necessarily for OO design as opposed to just technique), but whatever code they provide, or advice they give, should be highly considered.