代码改变世界

动手动脑五

2018-11-11 21:19  一念永恒s  阅读(192)  评论(0)  编辑  收藏  举报

1java中的异常处理捕获语句

package 动手动脑五;
import javax.swing.*;
public class AboutException {

    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        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");
         }
            
      }
    }

总结：try{}中是写可能发生运行错误的代码，catch{}中用于处理异常的代码，finally{}用于善后的代码，不管是否有异常发生，finally语句块中的语句始终保证被执行。

2多层的异常捕获

 1 public class CatchWho { 
 2     public static void main(String[] args) { 
 3         try { 
 4                 try { 
 5                     throw new ArrayIndexOutOfBoundsException(); 
 6                 } 
 7                 catch(ArrayIndexOutOfBoundsException e) { 
 8                        System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch"); 
 9                 }
10  
11             throw new ArithmeticException(); 
12         } 
13         catch(ArithmeticException e) { 
14             System.out.println("发生ArithmeticException"); 
15         } 
16         catch(ArrayIndexOutOfBoundsException e) { 
17            System.out.println(  "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
18         } 
19     } 
20 }

 1 public class CatchWho2 { 
 2     public static void main(String[] args) { 
 3         try {
 4                 try { 
 5                     throw new ArrayIndexOutOfBoundsException(); 
 6                 } 
 7                 catch(ArithmeticException e) { 
 8                     System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch"); 
 9                 }
10             throw new ArithmeticException(); 
11         } 
12         catch(ArithmeticException e) { 
13             System.out.println("发生ArithmeticException"); 
14         } 
15         catch(ArrayIndexOutOfBoundsException e) { 
16             System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
17         } 
18     } 
19 }

3

 1         int result;
 2         
 3         try {
 4             
 5             System.out.println("in Level 1");
 6 
 7            
 8              try {
 9                 
10                 System.out.println("in Level 2");
11   // result=100/0;  //Level 2
12                
13                  try {
14                    
15                      System.out.println("in Level 3");
16                       
17                      result=100/0;  //Level 3
18                 
19                 } 
20                 
21                 catch (Exception e) {
22                     
23                     System.out.println("Level 3:" + e.getClass().toString());
24                 
25                 }
26                 
27                 
28                 finally {
29                     
30                     System.out.println("In Level 3 finally");
31                 
32                 }
33                 
34                
35                 // result=100/0;  //Level 2
36 
37             
38                 }
39             
40             catch (Exception e) {
41                
42                  System.out.println("Level 2:" + e.getClass().toString());
43            
44              }
45              finally {
46                 
47                 System.out.println("In Level 2 finally");
48            
49              }
50              
51             // result = 100 / 0;  //level 1
52         
53         } 
54         
55         catch (Exception e) {
56             
57             System.out.println("Level 1:" + e.getClass().toString());
58         
59         }
60         
61         finally {
62            
63 .             System.out.println("In Level 1 finally");
64         
65         }
66     
67     }
68 
69 }

 1 public class SystemExitAndFinally {
 2 
 3     
 4     public static void main(String[] args)
 5     {
 6         
 7         try{
 8 
 9             
10             System.out.println("in main");
11             
12             throw new Exception("Exception is thrown in main");
13 
14                     //System.exit(0);
15 
16         
17         }
18         
19         catch(Exception e)
20 
21             {
22             
23             System.out.println(e.getMessage());
24             
25             System.exit(0);
26         
27         }
28         
29         finally
30         
31         {
32             
33             System.out.println("in finally");
34         
35         }
36     
37     }
38 
39 
40 }

实验总结：
如果finally块中的代码过多会导致字节码条数”膨胀”，因为finally中的字节码会被”复制”到try块和所有的catch块中，出异常了。System.out.println("F")不在finally里。而只有finally里的语句才会不论如何都会执行