Why is JFrame layout not the one I set?

Question

If I set a layout on a `JFrame` with `setLayout` and then retrieve it with `getLayout` then I get a different `LayoutManager`. What is going on here?? ``` public class Lay { public static void main(String[] args) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { java.awt.Container container = new javax.swing.JFrame(); //new javax.swing.JPanel(); java.awt.LayoutManager layout = new java.awt.GridLayout(); container.setLayout(layout); layout = container.getLayout(); System.err.println(layout); } }); } } ``` Gives ``` java.awt.BorderLayout[hgap=0,vgap=0] ``` but if I replace `JFrame` with `JPanel` I get ``` java.awt.GridLayout[hgap=0,vgap=0,rows=1,cols=0] ```

Accepted Answer

From the Java API for `JFrame`:

```
public void setLayout(LayoutManager manager)
```

Sets the `LayoutManager`. Overridden to conditionally forward the call to the `contentPane`. Refer to `RootPaneContainer` for more information.

And from the `RootPaneContainer` page:

This interface serves as a marker for Swing GUI builders that need to treat components like `JFrame`, that contain a single `JRootPane`, specially. For convenience `JFrame`, `JDialog`, `JWindow`, `JApplet` and `JInternalFrame`, by default, forward, by default, all calls to the `add`, `remove` and `setLayout` methods, to the `contentPane`. This means you can call:

```
rootPaneContainer.add(component);
```

instead of:

```
rootPaneContainer.getContentPane().add(component);
```

A `JRootPane` is a common component that all the heavyweight components use to appear like a native OS window. It handles the menu bar, close/minimize/maximize buttons, etc. `JFrame` tries to hide the fact that `JRootPane` does the real work from you, but in this case it just made things more confusing.

Why is JFrame layout not the one I set?

Solution

Problem