java异常处理

Posted 2020-08-20 张保海

一.动手动脑 

1）代码

import javax.swing.*;

class AboutException {
   public static void main(String[] a) 
   {
      double 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  "+k);
             //JOptionPane.showInternalConfirmDialog(null, k);
     }
  }


}

 

 

二.使用Java异常处理机制

注意throw和catch的对应关系，一个抛出必须有一个catch

 

三.动手动脑  

1）源代码

public class CatchWho { 
    public static void main(String[] args) { 
        try { 
                try { 
                    throw new ArrayIndexOutOfBoundsException(); //数组下标越界
                } 
                catch(ArrayIndexOutOfBoundsException e) { 
                       System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch"); 
                }
            throw new ArithmeticException(); //算术异常
        } 
        catch(ArithmeticException e) { //算数异常
            System.out.println("发生ArithmeticException"); 
        } 
        catch(ArrayIndexOutOfBoundsException e) { //数组下标越界
           System.out.println(  "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
        } 
    } 
}

3）结果分析
抛出两次异常，先处理第一次再处理第二次。

 

四.动手动脑  

1）源代码

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) { //数组下标越界
            System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
        } 
    } 
}

2）截图

3）结果分析

一个throw和catch后，才能执行下一个异常

 

五.动手动脑  

1）源代码

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");        
        }    
    }
}

2）结果截图

六.动手动脑  

1）源程序

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");
        }    
    }
}

 

2）结果截图

 

七.动手动脑 

编写一个程序，此程序在运行时要求用户输入一个 整数，代表某门课的考试成绩，程序接着给出“不及格”、“及格”、“中”、“良”、“优”的结论。
要求程序必须具备足够的健壮性，不管用户输入什 么样的内容，都不会崩溃。

1）源代码

import java.util.*;
public class Prograss {
    public static void main(String[] args) {

        Scanner sc=new Scanner(System.in);
        String pro;
        System.out.println("请输入成绩：");
        while(true){
        try{
            pro=sc.nextLine();
            if(pro.matches("\\\\D*")){
                throw new InException("输入有误！不是的不是数字！");
            }
            else{
                int proo=Integer.parseInt(pro);
                System.out.print("输入正确！");
                judge(proo);
                break;
            }
         }
        catch(InException e){
            System.out.print("请重新输入:");
        }
    }
        sc.close();
    }
    
    public static void judge(int pro){
        if(pro>=0&&pro<60)
            System.out.println("成绩不合格！");
        else if(pro<70)
            System.out.println("成绩合格！");
        else if(pro<80)
            System.out.println("成绩中！");
        else if(pro<90)
            System.out.println("成绩良！");
        else if(pro<=100)
            System.out.println("成绩优！");
        else
            System.out.println("输入成绩不符");
    }
}

class InException extends Exception{//
    public InException(String msg){
        super(msg);
    }
}