2020.10.27
一、今日学习内容
动手动脑
1、阅读代码，写出运行结果
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 }
【运行结果】
ArrayIndexOutOfBoundsException/内层try-catch
发生ArithmeticException
2、写出运行结果
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 }
【运行结果】
ArrayIndexOutOfBoundsException/外层try-catch
3、
1 public class EmbededFinally {
2
3
4 public static void main(String args[]) {
5
6 int result;
7
8 try {
9
10 System.out.println("in Level 1");
11
12
13 try {
14
15 System.out.println("in Level 2");
16 // result=100/0; //Level 2
17
18 try {
19
20 System.out.println("in Level 3");
21
22 result=100/0; //Level 3
23
24 }
25
26 catch (Exception e) {
27
28 System.out.println("Level 3:" + e.getClass().toString());
29
30 }
31
32
33 finally {
34
35 System.out.println("In Level 3 finally");
36
37 }
38
39
40 // result=100/0; //Level 2
41
42
43 }
44
45 catch (Exception e) {
46
47 System.out.println("Level 2:" + e.getClass().toString());
48
49 }
50 finally {
51
52 System.out.println("In Level 2 finally");
53
54 }
55
56 // result = 100 / 0; //level 1
57
58 }
59
60 catch (Exception e) {
61
62 System.out.println("Level 1:" + e.getClass().toString());
63
64 }
65
66 finally {
67
68 . System.out.println("In Level 1 finally");
69
70 }
71
72 }
73
74 }
【运行结果】
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
【总结】由此得出，代码运行类似于栈，先运行的后捕获，后抛出的先捕获
4、
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");
}
}
}
【运行结果】
in main
Exception is thrown in main
【结论】finally语句不一定被执行，当捕获错误处理完成并退出后便不再执行finally语句。
5、课程感受
通过这次课程，了解了Java的异常处理机制，可以有多个catch语句块，每个代码块捕获一种异常。在某个try块后有两个不同的catch 块捕获两个相同类型的异常是语法错误。使用catch语句，只能捕获Exception类及其子类的对象。因此，一个捕获Exception对象的catch语句块可以捕获所有“可捕获”的异常。将catch(Exception e)放在别的catch块前面会使这些catch块都不执行，因此Java不会编译这个程序。
二、遇到的问题
对于很多异常情况不知道，不会用
三、明日计划
明天总结Java项目中常见的异常情况
