Eine gute Antwort könnte sein:

In the body of the actionPerformed() method.

Changing the Color of a Frame

We will fill in the actionPerformed() body so that clicking the button changes the color of the frame. To change the color of the content pane of a frame, use the method setBackground( Color c ) . You can use one of the pre-defined colors like this:

getContentPane().setBackground( Color.red )

Other pre-defined colors are Color.green, Color.blue, Color.yellow, and so on. Here is the interesting part of our program:

public class ButtonDemo2 extends JFrame implements ActionListener
  JButton bChange;

  public ButtonDemo2()
    getContentPane().setLayout( new FlowLayout() );
    bChange = new JButton("Click Me!");
    bChange.addActionListener( this );
    getContentPane().add( bChange )

  public void actionPerformed( ActionEvent evt)
    repaint();  // ask the system to paint the screen.

  public static void main ( String[] args )
      . . . . .

The repaint() will be explained in the next page.


Fill in the blank so that the program changes the frame to blue when the button is clicked.