动手动脑5

题目一：请阅读并运行AboutException.java示例

AboutException.java

 1 import javax.swing.JOptionPane;
 2 
 3 public class AboutException {
 4     public static void main(String[] args) {
 5         int i=1,j=0,k;
 6         k=i/j;
 7         
 8         try {
 9             k=i/j;//Causes division-by-zero exception
10             //throw new Exception("Hello.Exception!");
11         }catch(ArithmeticException e) {
12             System.out.println("被0除."+e.getMessage());
13         }catch(Exception e) {
14             if(e instanceof ArithmeticException) {
15                 System.out.println("被0除");
16             }else {
17                 System.out.println(e.getMessage());
18             }
19         }finally {
20             JOptionPane.showConfirmDialog(null, "OK");
21         }
22     }
23 }

运行结果：

题目二：阅读以下代码（CatchWho.java）

CatchWho.java

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

执行结果：

CatchWho2.java

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

执行结果：

题目三：请先阅读 EmbedFinally.java示例，再运行它，观察其输出并进行总结。

EmbedFinally.java

 1 public class EmbededFinally {
 2     public static void main(String[] args) {
 3         int result;
 4         try {
 5             System.out.println("in Level 1");
 6             try {
 7                 System.out.println("in Level 2");
 8                 //result=100/0;//Level 2
 9                 try {
10                     System.out.println("in Level 3");
11                     result=100/0;//Level 
12                 }catch(Exception e) {
13                     System.out.println("Level 3:"+e.getClass().toString());
14                 }finally {
15                     System.out.println("In Level 3 finally");
16                 }
17                 //result=100/0;//Level 2
18             }catch(Exception e) {
19                 System.out.println("Level 2:"+e.getClass().toString());
20             }finally {
21                 System.out.println("In Level 2 finally");
22             }
23             //result=100/0;//Level 1
24         }catch(Exception e) {
25             System.out.println("Level 1:"+e.getClass().toString());
26         }finally {
27             System.out.println("In Level 1 finally");
28         }
29     }
30 }

执行结果为：

 将result的表达式换在第二个try里面，其执行代码为：

 1 public class EmbededFinally {
 2     public static void main(String[] args) {
 3         int result;
 4         try {
 5             System.out.println("in Level 1");
 6             try {
 7                 System.out.println("in Level 2");
 8                 result=100/0;//Level 2
 9                 try {
10                     System.out.println("in Level 3");
11                     //result=100/0;//Level 
12                 }catch(Exception e) {
13                     System.out.println("Level 3:"+e.getClass().toString());
14                 }finally {
15                     System.out.println("In Level 3 finally");
16                 }
17                 //result=100/0;//Level 2
18             }catch(Exception e) {
19                 System.out.println("Level 2:"+e.getClass().toString());
20             }finally {
21                 System.out.println("In Level 2 finally");
22             }
23             //result=100/0;//Level 1
24         }catch(Exception e) {
25             System.out.println("Level 1:"+e.getClass().toString());
26         }finally {
27             System.out.println("In Level 1 finally");
28         }
29     }
30 }

执行结果为：

  将result的表达式换在第一个try里面，其执行代码为：

 1 public class EmbededFinally {
 2     public static void main(String[] args) {
 3         int result;
 4         try {
 5             System.out.println("in Level 1");
 6             try {
 7                 System.out.println("in Level 2");
 8                 //result=100/0;//Level 2
 9                 try {
10                     System.out.println("in Level 3");
11                     //result=100/0;//Level 
12                 }catch(Exception e) {
13                     System.out.println("Level 3:"+e.getClass().toString());
14                 }finally {
15                     System.out.println("In Level 3 finally");
16                 }
17                 //result=100/0;//Level 2
18             }catch(Exception e) {
19                 System.out.println("Level 2:"+e.getClass().toString());
20             }finally {
21                 System.out.println("In Level 2 finally");
22             }
23             result=100/0;//Level 1
24         }catch(Exception e) {
25             System.out.println("Level 1:"+e.getClass().toString());
26         }finally {
27             System.out.println("In Level 1 finally");
28         }
29     }
30 }

执行结果为：

总结：

在try..catch...finally语句中，try里面的是率先执行的，若是try内的语句有错误，catch中的语句才会执行，若是无错误，便会执行finally内的语句。

题目四：辨析：finally语句块一定会执行吗？ 请通过 SystemExitAndFinally.java示例程序回答上述问题

SystemExitAndFinally.java

 1 public class SystemExitAndFinally {   
 2     public static void main(String[] args){
 3         try{
 4             System.out.println("in main");
 5             throw new Exception("Exception is thrown in main");
 6             //System.exit(0);
 7         }catch(Exception e){
 8             System.out.println(e.getMessage());
 9             System.exit(0);
10         }finally{
11             System.out.println("in finally");
12         }
13     }
14 }

执行结果为：

 若程序改为：

 则会出现以下错误：

 结论：finally代码块不一定会被执行