Java基础之异常处理操作示例

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");
  }
}

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{}:");
  }
}

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.");
     }
  }
}

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);
  }
}

try{

}
catch(ArithmeticException|ArrayIndexOutOfBoundsException e){//同时捕获多个异常
}

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);
      }
    }
  }
}