exceptionapplet.java

我在学习JAVA的讲义

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class ExceptionApplet extends Applet implements ActionListener
{   Label L1,L2;
    TextField tf1,tf2;
    String answerStr;
    double d1,d2;

    public void init( )
    {   L1=new Label("请输入0到100之间的整数");
        add(L1);
        tf1=new TextField(6);
        add(tf1);
        tf2=new TextField(6);
        add(tf2);
        L2=new Label("两数相除的结果：                                                  ");
        add(L2);
        tf1.addActionListener(this);
        tf2.addActionListener(this);
    }
    public void actionPerformed(ActionEvent evt)
    {   try
        {   d1=Double.valueOf(tf1.getText( )).doubleValue( );
            d2=Double.valueOf(tf2.getText( )).doubleValue( );
            // valueOf(String s) 可能抛出异常 NumberFormatException
            L2.setText("两数相除的结果：   "+Result( ));
            // 调用 Result( ) 方法可能抛出 NumberRangeException 异常
        }
        catch(NumberFormatException e)
        {   answerStr="输入的必须是数字";
            L2.setText(answerStr);
        }
        catch(NumberRangeException ee)
        {   answerStr=ee.getMessage( );
            L2.setText(answerStr);
        }
        repaint( );
    }
    public double Result( ) throws NumberRangeException
    {   double answer=0;
        try
        {   if((d1<0)||(d2<0)||(d1>100)||(d2>100))
            {   NumberRangeException ee=new NumberRangeException("输入的数字不在指定的范围！请重新输入。");
                throw ee;
            }
            answer=d1/d2;
        }
        catch(ArithmeticException eee)
        {   answerStr=eee.toString( );
        }
        return answer;
    }
}
class NumberRangeException extends Exception
{   NumberRangeException(String msg)
    {   super(msg);   }
    //子类调用父类的带参数的构造函数
}