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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 0java.lang.ArithmeticException: / by zerom/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.javalydia@lydia:~/sgy/java_learn/exception$ java Test 9 1this is finally!m/n=9lydia@lydia:~/sgy/java_learn/exception$ java Test 9 0java.lang.ArithmeticException: / by zerothis 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  0div--->java.lang.ArithmeticException: / by zerom/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  0div--->java.lang.ArithmeticException: / by zeromain-->java.lang.ArithmeticException: / by zerom/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  0div--->java.lang.ArithmeticException: / by zeromain-->java.lang.ArithmeticException: / by zerom/n=0lydia@lydia:~/sgy/java_learn/exception$ java Test 9  amain-->java.lang.NumberFormatException: For input string: "a"m/n=0lydia@lydia:~/sgy/java_learn/exception$ java Test 9main-->java.lang.ArrayIndexOutOfBoundsException: 1m/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.javaTest.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.javaTest.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  0div--->java.lang.ArithmeticException: / by zeromain-->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  0div--->java.lang.ArithmeticException: / by zerodiv-->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  0div--->java.lang.ArithmeticException: / by zeromain-->java.lang.ArithmeticException: / by zerom/n=0

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