当我尝试运行此代码时，我收到此错误：
Multiple markers at this line
- Line breakpoint:CastleDefenders [line: 45] - CastleDefenders()
- The method addActionListener(ActionListener) in the type AbstractButton is not applicable
for the arguments (CastleDefenders)
代码：
public CastleDefenders(){
button = new JButton("Go!");
lvl1.setToolTipText("Play the game on Easy");
lvl2.setToolTipText("Play the game on Normal");
lvl3.setToolTipText("Play the game on Hard");
lvl1.setActionCommand("Easy");
lvl2.setActionCommand("Normal");
lvl3.setActionCommand("Hard");
lvls.add(lvl1);
lvls.add(lvl2);
lvls.add(lvl3);
pnl2.add(lvl1);
pnl2.add(lvl2);
pnl2.add(lvl3);
button.addActionListener(this);
tlkt = Toolkit.getDefaultToolkit();
timer = new Timer();
pnl2.setBounds(50, 5, 1, 10);
btn.setBounds(220, 240, 5, 1);
f.setJMenuBar(mb2);
g.setJMenuBar(mb2);
mnuFile.add(mnuItemQuit);
mnuHelp.add(mnuItemAbout);
mb.add(mnuFile);
mb.add(mnuHelp);
mb2.add(mnuFile);
mb2.add(mnuHelp);
pnl.add(btn);
pnl2.add(lbl);
pnl2.add(button);
lbl.setBounds(0, 240, 10, 2);
lbl.setEditable(false);
f.getContentPane().setLayout(new BorderLayout());
f.getContentPane().add(pnl, BorderLayout.CENTER);
f.addWindowListener(new ListenCloseWdw());
g.getContentPane().setLayout(new BorderLayout());
g.getContentPane().add(pnl2);
g.addWindowListener(new ListenCloseWdw());
mnuItemAbout.addActionListener(new GetAboutInfo());
btn.addActionListener(new GetButtonClick());
mnuItemQuit.addActionListener(new ListenMenuQuit());
add(button);
}