下述代码中,如果单击 TEST按,标准输出的消息是( )。 public class Exercise extends JFrame{ public Exercise(){ super("事件测试"); JButton b=new JButton("TEST"); Tester t=new Tester(); b.addMouseListener(t); b.addActionListener(t); this.add(b); this.setSize(200, 150); this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.setVisible(true); } } class Tester implements MouseListener,,ActionListener{ public void actionPerformed(ActionEvent e){ System.out.println("按发生动作"); } public void mouseClicked(MouseEvent e){ System.out.println("按被单击"); } public void mousePressed(MouseEvent e){} public void mouseReleased(MouseEvent e){} public void mouseEntered(MouseEvent e){} public void mouseExited(MouseEvent e){} }