BoxLayout for a JFrame

Question

Could you help me understand what is going on here. I consulted Javadoc: JFrame has setLayout method. So, what sharing error springs out is a mystery to me.

Answer 1

Try this one on JFrame#getContentPane()

this.setLayout(new BoxLayout(this.getContentPane(), BoxLayout.X_AXIS));

Read more How to Use BoxLayout

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All the components are added in JFrame's content pane.

Read more Adding Components to the Content Pane

Here is the pictorial representation how JFrame looks like

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EDIT

From comments:

Well, not clear anyway. I analyze it like this: BoxLayout class needs to know it target. JFrame has setLayoutt method and needs to know its layout.

this.setLayout(manager) internally calls getContentPane().setLayout(manager);

The below line

this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS));

is converted to below line that is not correct.

this.getContentPane().setLayout(new BoxLayout(this, BoxLayout.X_AXIS));

For more detail have a look at Source code