Eine gute Antwort könnte sein:

The answer is given in the completed program, below.

Complete Program

The following is a complete program, suitable for copying to a file and running.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ButtonDemo2 extends JFrame implements ActionListener
  JButton bChange;

  // constructor
  public ButtonDemo2()
        setLayout( new FlowLayout() ); // choose the layout manager
    bChange = new JButton("Click Me!");// construct a Button
    bChange.addActionListener( this ); // register the ButtonDemo2 object
                                       // as the listener for its Button.
    getContentPane().add( bChange );   // add the button to the container

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

  public static void main ( String[] args )
    ButtonDemo2 frm = new ButtonDemo2();

    WindowQuitter wquit = new WindowQuitter();
    frm.addWindowListener( wquit );

    frm.setSize( 200, 150 );
    frm.setVisible( true );


class WindowQuitter extends WindowAdapter
  public void windowClosing( WindowEvent e )
    System.exit( 0 );  // what to do for this event--exit the program

The repaint() method tells the system to repaint the screen sometime soon because we have changed something. The system will do this when it is ready. Don't call paint().


Should the entire frame be repainted every time a button is clicked?