How do I change JPanel inside a JFrame on the fly?

frame.setContentPane(newContents());
frame.revalidate(); // frame.pack() if you want to resize.

Remember, Java use 'copy reference by value' argument passing. So changing a variable wont change copies of the reference passed to other methods.

Also note JFrame is very confusing in the name of usability. Adding a component or setting a layout (usually) performs the operation on the content pane. Oddly enough, getting the layout really does give you the frame's layout manager.

Hope this piece of code give you an idea of changing jPanels inside a JFrame.

public class PanelTest extends JFrame {

        Container contentPane;

        public PanelTest()  {
           super("Changing JPanel inside a JFrame");
           contentPane=getContentPane();
        }

        public void createChangePanel() {
           contentPane.removeAll();
           JPanel newPanel=new JPanel();
           contentPane.add(newPanel);
           System.out.println("new panel created");//for debugging purposes
           validate();
           setVisible(true);
        }
}

I was having exactly the same problem!! Increadible!! The solution I found was:

1. Adding all the components (JPanels) to the container;
2. Using the setVisible(false) method to all of them;
3. On user action, setting setVisible(true) to the panel I wanted to show.

// Hiding all components (JPanels) added to a container (ex: another JPanel)
for (Component component : this.container.getComponents()) {
      component.setVisible(false);
}

// Showing only the selected JPanel, the one user wants to see
panel.setVisible(true);

No revalidate(), no validate(), no CardLayout needed.