阅读下列程序,写出程序功能。import j ava. awt. *;import j avax. swing. *;import j ava. aw
阅读下列程序,写出程序功能。
import j ava. awt. *;
import j avax. swing. *;
import j ava. awt. event. *;
public class C3401 implements ActionListener
{
JFrame. frmFrame;
JButton btnUp, btnDown;
public C3401()
{
frmFrame=new JFrame("按钮应用") ;
frmFrame. setLayout(new CridLayout(2, 1) ) ;
btnUp=new JButton("上") ;
btnUp. setActionCommand("btnUp") ;
btnUp. addActionListener(this) ;
btnDown=new JButton("下") ;
btnDown. setActionCommand("btnDown") ;
btnDown. addActionListener(this) ;
frmFrame. add(btnUp) ;
frmFrame. add(btnDown) ;
frmFrame. pack() ;
frmFrame. setVisible(true) ;
}
public void actionPerformed(ActionEvent e)
{
String cmd=e. getActionCommand() ;
if(cmd. equals("btnDown")
if(btnUp. getBackground() ==Color. BLUE.
btnUp. setBackground(Color. red) ;
else
btnUp. setBackground(Color. blue) ;
else
if(btnDown. getBackground() ==Color. BLUE.
btnDown. setBackground (Color. red) ;
else
btnDown. setBackground(Color. blue) ;
}
public static void main(String[] args)
{
new C3401() ;
}
}