根据课上的课件进行练习
1、阅读以下代码（CatchWho.java），写出程序运行结果：
1 package exception;
2
3 public class CatchWho {
4 public static void main(String[] args) {
5 try {
6 try {
7 throw new ArrayIndexOutOfBoundsException();
8 }
9 catch(ArrayIndexOutOfBoundsException e) {
10 System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch");
11 }
12
13 throw new ArithmeticException();
14 }
15 catch(ArithmeticException e) {
16 System.out.println("发生ArithmeticException");
17 }
18 catch(ArrayIndexOutOfBoundsException e) {
19 System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch");
20 }
21 }
22 }
结果：
ArrayIndexOutOfBoundsException/内层try-catch
发生ArithmeticException
2、写出CatchWho2.java程序运行的结果
1 package exception;
2
3 public class CatchWho2 {
4 public static void main(String[] args) {
5 try {
6 try {
7 throw new ArrayIndexOutOfBoundsException();
8 }
9 catch(ArithmeticException e) {
10 System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch");
11 }
12 throw new ArithmeticException();
13 }
14 catch(ArithmeticException e) {
15 System.out.println("发生ArithmeticException");
16 }
17 catch(ArrayIndexOutOfBoundsException e) {
18 System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch");
19 }
20 }
21 }
结果：ArrayIndexOutOfBoundsException/外层try-catch
3、阅读 EmbedFinally.java示例，再运行它，观察其输出并进行总结
1 package exception;
2
3
4 class EmbededFinally {
5 public static void main(String args[]) {
6
7 int result;
8
9 try {
10
11 System.out.println("in Level 1");
12
13
14 try {
15
16 System.out.println("in Level 2");
17 // result=100/0; //Level 2
18
19 try {
20
21 System.out.println("in Level 3");
22
23 result=100/0; //Level 3
24
25 }
26
27 catch (Exception e) {
28
29 System.out.println("Level 3:" + e.getClass().toString());
30
31 }
32
33
34 finally {
35
36 System.out.println("In Level 3 finally");
37
38 }
39
40
41 // result=100/0; //Level 2
42
43
44 }
45
46 catch (Exception e) {
47
48 System.out.println("Level 2:" + e.getClass().toString());
49
50 }
51 finally {
52
53 System.out.println("In Level 2 finally");
54
55 }
56
57 // result = 100 / 0; //level 1
58
59 }
60
61 catch (Exception e) {
62
63 System.out.println("Level 1:" + e.getClass().toString());
64
65 }
66
67 finally {
68
69 System.out.println("In Level 1 finally");
70
71 }
72
73 }
74
75 }
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
try捕捉到的异常会从一到二进行抛出，finally的异常会从二到一抛出。
4、finally语句块一定会执行吗？
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 }
结果：
in main
Exception is thrown in main
finally不一定会执行。
当程序执行try块，catch块时遇到return语句或者throw语句，这两个语句都会导致该方法立即结束，所以系统并不会立即执行这两个语句，而是 去寻找该异常处理流程中的finally块，如果没有finally块，程序立即执行return语句或者throw语句，方法终止。如果有 finally块，系统立即开始执行finally块，只有当finally块执行完成后，系统才会再次跳回来执行try块、catch块里的 return或throw语句，如果finally块里也使用了return或throw等导致方法终止的语句，则finally块已经终止了方法，不用 再跳回去执行try块、catch块里的任何代码了。
综上：尽量避免在finally块里使用return或throw等导致方法终止的语句，否则可能出现一些很奇怪的情况！