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