Question

java主程序里面catch（）语句中catch( MyException e)中的MyException下面显示红线错误，跪求解释

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
public class Shiyan extends JFrame implements CaretListener
{ private static JTextArea text_1;
private static JLabel jl1;
private JLabel jl2;
private JButton bt1,bt2,bt3,bt4;
private JComboBox cbx;
static JPanel pane2=new JPanel(new GridLayout(1,2));
static JPanel pane1=new JPanel(new GridLayout(1,2));
public Shiyan()
{

super("猫狗小虎威");
Container contentPane = getContentPane();
this.setLocation(200,200);
this.setBounds(300,240,360,200);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.getContentPane().setLayout(new GridLayout(5,1));

text_1=new JTextArea(4,4);

//JPanel pane1=new JPanel(new GridLayout(1,2));
this.getContentPane().add(pane1);

//JPanel pane2=new JPanel(new GridLayout(1,2));
this.getContentPane().add(pane2);
JPanel pane3=new JPanel(new GridLayout(1,2));
this.getContentPane().add(pane3);
JPanel pane4=new JPanel(new GridLayout(1,2));
this.getContentPane().add(pane4);
pane2.add(text_1);

JLabel jl1=new JLabel(" ——————异常处理部分——————");
pane1.add(jl1);
JLabel jl2=new JLabel("标签B");
pane2.add(jl2);

bt1=new JButton("插入");
bt1.addActionListener((ActionListener) this);

pane3.add(bt1);
setVisible(true);

JComboBox jc = new JComboBox();
pane3.add(jc);
jc.addItem("英文单词");

setVisible(true);

}

public void actionPerformed(ActionEvent e) throws MyException
{if(e.getSource()==bt1)
if(text_1.getText().equals("123"))
{throw new MyException("错误：输入不可以是123啊");}
}

class MyException extends Exception
{
String message; //定义String类型变量
public MyException(String ErrorMessagr)
{ message = ErrorMessagr;
}
public String getMessage(){ //覆盖getMessage()方法
return message;
}
}

public void caretUpdate(CaretEvent e)
{
// TODO Auto-generated method stub

}

public static void main(String arg[])
{ try
{new Shiyan();
}

catch(MyException e){//System.out.println(e.getMessage());
JOptionPane.showMessageDialog(pane2,jl1+"e.getMessage()");
}
catch(Exception e){System.out.println(e.getMessage());}

finally{}
}

Answer 1

（1）既然要让窗口作为自己的监听器，那么看你的程序内容，实现监听器只要实现ActionListener接口就完全可以满足要求啊
（2）虽然CaretListener和ActionListener都继承自超级接口EventListener，但若非要让它实现CaretListener接口，反而不能强制转换成ActionListener（程序不会提示有红线），而添加监听器的方法addActionListener(…)的参数必须是ActionListener
（3）如果你把实现接口改成ActionListener，你会发现接口回调的方法actionPerformed（）是不允许抛出异常的，即不允许方法throws，若有异常必须则必须在方法体内try……catch……掉

希望可以帮到你。。。

Answer 2

错误：在相应的 try 语句主体中不能抛出异常 Shiyan.MyException，所以也就没有必要catch了。
你只是new Shiyan();调用构造方法的时候不会抛出MyException。
应该直接在你的 actionPerformed里面catch 就不用throws MyException了

Answer 3

肯定啊...哪有MyException