Java基础：异常处理

示例代码：

public class ExecDemo {
public static void main(String[] args) {
int[] nums = new int[4];
System.out.println("before the exception:");
try { //try代码块 try catch代码块可以嵌套
try{
nums[7] = 10; //数组越界
System.out.println("no exception:");
}catch(ArithmeticException e){
e.printStackTrace();
}
}catch(ArithmeticException e) { //catch代码块 多个catch块
e.printStackTrace(); //打印异常信息
}catch(ArrayIndexOutOfBoundsException e){ // 捕获数组越界错误捕获子类异常
e.printStackTrace();
}catch(Throwable e){ //捕获超类异常 Throwable是所有异常的超类
e.printStackTrace();
}
System.out.println("after the exception");
}
}
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抛出异常：
public class ThrowDemo {
public static void main(String[] args) {
try {
System.out.println("before throw:");
throw new ArithmeticException(); //throw关键字抛出一个ArithmeticException()异常(手动抛出异常)
} catch (ArithmeticException e) { //捕获异常
System.out.println("exception caught:");
}
System.out.println("after try{}catch{}:");
}
}
----------------------------------------------------------------------------
重新抛出异常：
class Rethrow {
public static void genException() {
int[] numer = {2,4,6,8,10,12};
int[] demon = {2,0,3,4,0};
for(int i=0;i < numer.length;i++){
try { //try代码块
System.out.println(numer[i]/demon[i]);
} catch (ArithmeticException e) { //多个catch()块
System.out.println("can't dev by zero:");
}catch(ArrayIndexOutOfBoundsException e) {
System.out.println("no error:");
throw e; //throw 重写抛出异常
}
}
}
}
public class RethrowDemo{
public static void main(String args[]) {
try {
Rethrow.genException();
} catch (ArrayIndexOutOfBoundsException e) { //捕获重新抛出的异常
System.out.println("error error error error error:");
}
finally{ //finally代码块在try catch执行完时执行的。
System.out.println("Leaving try.");
}
}
}
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throws语句：一个方法产生自己不做处理的异常，用throws抛出到外层（谁调用，谁处理异常）
public class ThrowsDemo {
public static char prompt(String str) throws java.io.IOException{//prompt()方法产生自己不做处理的IOException异常，抛出到外层，谁调用谁处理异常
System.out.print(str +":");
return (char) System.in.read();
}
public static void main(String[] args) {
char ch;
try {
ch = prompt("enter a letter"); //prompt()可能抛出异常，
} catch (java.io.IOException e) { //捕获prompt()抛出的异常
System.out.println("IOException occurred");
ch = 'x';
}
System.out.println("you pressed:"+ ch);
}
}
------------------------------------------------------------------------------------
可以用一个catch()捕获多个异常：
try{
}
catch(ArithmeticException|ArrayIndexOutOfBoundsException e){//同时捕获多个异常
}
-----------------------------------------------------------------------------------
自定义异常：
class NonIntResultException extends Exception{ //自定义异常继承子Exception
int n ,d;
NonIntResultException(int i,int j){
n = i;
d = j;
}
public String toString() {
return "result of "+ n +"/"+ d +" is non-integer.";
}
}
public class CustomExceptionDemo {
public static void main(String[] args) {
int numer[] = {4,8,15,32,64,127,256,512};
int denom[] = {2,0,4,4,0,8};
for(int i=0;i<numer.length;i++) {
try {
if((numer[i]%2)!=0) {
throw new NonIntResultException(numer[i],denom[i]); //抛出自定义异常
}
System.out.println(numer[i] +"/"+ denom[i] +" is "+ numer[i]/denom[i]);
} catch (ArithmeticException e) { //捕获ArithmeticException异常
System.out.println("can't divide by zero!");
}catch (ArrayIndexOutOfBoundsException e) { //捕获ArrayIndexOutOfBoundsException 异常
System.out.println("no matching element found.");
}catch (NonIntResultException e) { //捕获自定义异常
System.out.println(e);
}
}
}
}

Java基础：异常处理

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