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java学习记录之异常
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内容图文
异常的分类
- 自己需要处理的
try, catch, finally
- 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:
-
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
-
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
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