异常的分类

1. 自己需要处理的

try, catch, finally

2. 让别人处理的

throws

实际的例子

Test.java

public class Test {     public static void main (String  args[]) {              int m = Integer.parseInt(args[0]);int n = Integer.parseInt(args[1]);int r = div(m, n);System.out.println("m/n=" + r);}public static int div(int m, int n) {int r = 0;r= m/n;return r;}}

执行 java Test 9 0会抛出算数异常，那怎么捕捉呢？

public class Test {     public static void main (String  args[]) {              int m = Integer.parseInt(args[0]);int n = Integer.parseInt(args[1]);int r = div(m, n);System.out.println("m/n=" + r);}public static int div(int m, int n) {int r = 0;try {r = m/n;} catch (ArithmeticException e) {System.out.println(e);}return r;}}

执行结果

lydia@lydia:~/sgy/java_learn/exception$ java Test 9 0
java.lang.ArithmeticException: / by zero
m/n=0

finally就是不管是否发生异常，都会最终执行到的语句！

加上finally看一下效果！

	public static int div(int m, int n) {int r = 0;try {r = m/n;} catch (ArithmeticException e) {System.out.println(e);} finally {System.out.println("this is finally!");}return r;}

执行的结果，9/1， 或者9/0最终都会执行finally的语句

lydia@lydia:~/sgy/java_learn/exception$ javac Test.java
lydia@lydia:~/sgy/java_learn/exception$ java Test 9 1
this is finally!
m/n=9
lydia@lydia:~/sgy/java_learn/exception$ java Test 9 0
java.lang.ArithmeticException: / by zero
this is finally!
m/n=0

怎么让别人处理

例如div函数自己本身不处理，扔给main方法

public class Test {     public static void main (String  args[]) {              int m = Integer.parseInt(args[0]);int n = Integer.parseInt(args[1]);int r = 0;try {r = div(m, n);} catch (ArithmeticException e) {System.out.println(e);}System.out.println("m/n=" + r);}public static int div(int m, int n) throws ArithmeticException {int r = 0;r = m / n;return r;}}

main和div怎么一起处理这个异常？

现在的程序只会在div中处理这个异常！
Test.java

public class Test {     public static void main (String  args[]) {              int m = Integer.parseInt(args[0]);int n = Integer.parseInt(args[1]);int r = 0;try {r = div(m, n);} catch (ArithmeticException e) {System.out.println("main-->"+e);}System.out.println("m/n=" + r);}public static int div(int m, int n) throws ArithmeticException {int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);}return r;}}

执行的结果只有div会处理这个异常

lydia@lydia:~/sgy/java_learn/exception$ java Test 9  0
div--->java.lang.ArithmeticException: / by zero
m/n=0

需要通过手动抛出异常！

修改后的代码！

	public static int div(int m, int n) throws ArithmeticException {int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);throw e;}return r;}

lydia@lydia:~/sgy/java_learn/exception$ java Test 9  0
div--->java.lang.ArithmeticException: / by zero
main-->java.lang.ArithmeticException: / by zero
m/n=0

异常太多，不需要一个个列出来，捕获父类异常，或者大类的异常即可

Test.java

public class Test {     public static void main (String  args[]) {              int m = 0;		int n =0;int r = 0;try {m = Integer.parseInt(args[0]);n = Integer.parseInt(args[1]);r = div(m, n);} catch (ArithmeticException e) {System.out.println("main-->"+e);} catch (RuntimeException e) {System.out.println("main-->"+e);}System.out.println("m/n=" + r);}public static int div(int m, int n) throws ArithmeticException {int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);throw e;}return r;}}

执行结果

lydia@lydia:~/sgy/java_learn/exception$ java Test 9  0
div--->java.lang.ArithmeticException: / by zero
main-->java.lang.ArithmeticException: / by zero
m/n=0
lydia@lydia:~/sgy/java_learn/exception$ java Test 9  a
main-->java.lang.NumberFormatException: For input string: "a"
m/n=0
lydia@lydia:~/sgy/java_learn/exception$ java Test 9
main-->java.lang.ArrayIndexOutOfBoundsException: 1
m/n=0

人为的new execption

Test.java
div函数改成下面这样！

	public static int div(int m, int n)  {int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);throw new Exception("My error!");}return r;}

编译不通过，new Execption 必须处理或者抛出！

lydia@lydia:~/sgy/java_learn/exception$ javac Test.java
Test.java:27: 错误: 未报告的异常错误Exception; 必须对其进行捕获或声明以便抛出throw new Exception("My error!");^
1 个错误

继续更改，div函数

	public static int div(int m, int n) throws Exception{int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);throw new Exception("My error!");}return r;}

编译结果还是一样，Main函数里面也需要处理！

lydia@lydia:~/sgy/java_learn/exception$ javac Test.java
Test.java:11: 错误: 未报告的异常错误Exception; 必须对其进行捕获或声明以便抛出r = div(m, n);^
1 个错误

对Main方法增加 catch Exception，处理这个异常，就不会有问题

public class Test {     public static void main (String  args[]) {              int m = 0;		int n =0;int r = 0;try {m = Integer.parseInt(args[0]);n = Integer.parseInt(args[1]);r = div(m, n);} catch (ArithmeticException e) {System.out.println("main-->"+e);} catch (RuntimeException e) {System.out.println("main-->"+e);} catch (Exception e) {System.out.println("main-->"+e);}System.out.println("m/n=" + r);}public static int div(int m, int n) throws Exception{int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);throw new Exception("My error!");}return r;}}

执行的结果

lydia@lydia:~/sgy/java_learn/exception$ java Test 9  0
div--->java.lang.ArithmeticException: / by zero
main-->java.lang.Exception: My error!
m/n=0

或者直接在div当中处理掉！
在div中增加try catch的语句，直接本方法处理！

	public static int div(int m, int n) throws Exception{int r = 0;try {r = m / n;} catch (ArithmeticException e) {System.out.println("div--->"+ e);try {throw new Exception("My error!");} catch (Exception e1) {System.out.println("div-->"+e1);}}return r;}

lydia@lydia:~/sgy/java_learn/exception$ java Test 9  0
div--->java.lang.ArithmeticException: / by zero
div-->java.lang.Exception: My error!
m/n=0

PS:

1. try或catch块中有return或throw语句，会先执行finally块，再返回来执行return或throw语句

2. 对于“不可查异常”, 系统也会抛出它，写不写throws效果一样
   即throws ArithmeticException不写， main方法仍能够正常捕捉到！会自动抛出

	public static int div(int m, int n) throws ArithmeticException {

执行的结果

lydia@lydia:~/sgy/java_learn/exception$ java Test 9  0
div--->java.lang.ArithmeticException: / by zero
main-->java.lang.ArithmeticException: / by zero
m/n=0