java异常处理课后作

1、动手动脑

源码

import javax.swing.*;

class AboutException {
   public static void main(String[] a)
   {
      int i=1, j=0, k;
      k=i/j;

 try
 {
  
  k = i/j;    // Causes division-by-zero exception
  //throw new Exception("Hello.Exception!");
 }
 
 catch ( ArithmeticException e)
 {
  System.out.println("被0除.  "+ e.getMessage());
 }
 
 catch (Exception e)
 {
  if (e instanceof ArithmeticException)
   System.out.println("被0除");
  else
  { 
   System.out.println(e.getMessage());
   
  }
 }

 
 finally
     {
       JOptionPane.showConfirmDialog(null,"OK");
     }

}

}

 

 

结果：

 

              

java把可能会发生错误的代码放进try语句块中，catch语句块中的代码用于处理错误，不管是否有异常发生，finally语句块中的语句始终保证被执行。如果没有提供合适的异常处理代码，JVM会结束掉整个应用程序。

2、动手动脑

源码

public class CatchWho {
    public static void main(String[] args) {
        try {
             try {
                 throw new ArrayIndexOutOfBoundsException();
             }
             catch(ArrayIndexOutOfBoundsException e) {
                 System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch");
             }
 
            throw new ArithmeticException();
        }
        catch(ArithmeticException e) {
            System.out.println("发生ArithmeticException");
        }
        catch(ArrayIndexOutOfBoundsException e) {
           System.out.println(  "ArrayIndexOutOfBoundsException" + "/外层try-catch");
        }
    }
}

结果

ArrayIndexOutOfBoundsException/内层try-catch
发生ArithmeticException

源码

public class CatchWho2 {
    public static void main(String[] args) {
        try {
             try {
                 throw new ArrayIndexOutOfBoundsException();
             }
             catch(ArithmeticException e) {
                 System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch");
             }
            throw new ArithmeticException();
        }
        catch(ArithmeticException e) {
            System.out.println("发生ArithmeticException");
        }
        catch(ArrayIndexOutOfBoundsException e) {
            System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch");
        }
    }
}

结果

ArrayIndexOutOfBoundsException/外层try-catch

3、动手动脑

源码

public class EmbededFinally {

   
 public static void main(String args[]) {
       
  int result;
       
  try {
           
   System.out.println("in Level 1");

          
    try {
               
    System.out.println("in Level 2");
  // result=100/0;  //Level 2
              
     try {
                  
      System.out.println("in Level 3");
                     
      result=100/0;  //Level 3
               
    }
               
    catch (Exception e) {
                   
     System.out.println("Level 3:" + e.getClass().toString());
               
    }
               
               
    finally {
                   
     System.out.println("In Level 3 finally");
               
    }
               
              
    // result=100/0;  //Level 2

           
    }
           
   catch (Exception e) {
              
     System.out.println("Level 2:" + e.getClass().toString());
          
    }
    finally {
               
    System.out.println("In Level 2 finally");
          
    }
            
   // result = 100 / 0;  //level 1
       
  }
       
  catch (Exception e) {
           
   System.out.println("Level 1:" + e.getClass().toString());
       
  }
       
  finally {
          
.    System.out.println("In Level 1 finally");
       
  }
   
 }

}

结果

in Level 1
in Level 2
in Level 3
Level 3:class java.lang.ArithmeticException
In Level 3 finally
In Level 2 finally
In Level 1 finally

4、动手动脑

源码

public class SystemExitAndFinally {

   
 public static void main(String[] args)
    {
       
  try{

           
   System.out.println("in main");
           
   throw new Exception("Exception is thrown in main");

              //System.exit(0);

       
  }
       
  catch(Exception e)

         {
           
   System.out.println(e.getMessage());
           
   System.exit(0);
       
  }
       
  finally
       
  {
           
   System.out.println("in finally");
       
  }
   
 }

}

结果

in main
Exception is thrown in main

当存在try中有throw new Exception（）时，finally不会执行

 

课堂测验

 

输入整数判断成绩等级，抛出异常

 

import java.util.Scanner;
class MyException extends Exception
{
 public MyException(String messege)
 {
  super(messege);
 }
}

class numbertest //自定义异常类
{
 public int score(int a) throws MyException  //当a<0或a>100时,抛出一个自定义异常
 {
  
  if(a<0 || a>100) 
  {
   throw new MyException("成绩输入有误");//抛出异常
  }  
  return a;//返回a
 }
}

public class test1{
 public static void main(String[] args) throws MyException
 {
  try
  {
   Scanner scan=new Scanner(System.in);
   System.out.println("请输入分数");
   int n = 0,i;
   n=scan.nextInt();
   numbertest k=new numbertest(); 
   try
   {
    int t=k.score(n);
    i=n/10;
    switch(i)
    {
    case 10:
    case 9:
     System.out.println("优");break;
    case 8:
     System.out.println("良");break;
    case 7:
     System.out.println("中");break;
    case 6:
     System.out.println("及格");break;
    default:
     System.out.println("不及格");break;
    }
   }
   catch(MyException e)
   {
    System.out.println(e);//输出
   }
   }
   catch(Exception e)//由于变量定义为int型，所以输入字符时，则输出该异常信息
   {
    System.out.println("输入格式不合法");//输出
   }
  }
}

结果