Java exception -例外處理

Runtime exception: 非程式設計師所能預期到的錯誤.可直接拋出.

如果類似檔案找不到 ,這種可預期的錯誤狀況便要利用

try ..catch 把錯誤接收起來並做適當的處理

import java.io.*; 
public class ExceptionDemo { 
     public static void main(String[] args) throws FileNotFoundException{ 
          int i =Integer.parseInt("r"); // this is a runtime exception 
          System.out.println(i); 
          //using a try catch block to catch checked exception 
          try { 
               FileReader fr = new FileReader(new File("xxx.txt")); 
          } catch (FileNotFoundException e) { 
               // TODO Auto-generated catch block 
               e.printStackTrace(); 
          } 
          //or throw out this exception to the caller. 
          FileReader fr = new FileReader(new File("xxx.txt")); 
     } 
} 

Following is a fail case.

public class UnreachableDemo {
 public static void main(String[] args){
  int [] k =new int []{1,2,3};
  for(int i = 0 ; i < k.length+1 ; i++ ){
   System.out.println(k[i]);
  }
  System.out.println("arrive here?");
 }
}

Following is a success case.

public class ReachableDemo {
 public static void main(String[] args){
  int [] k =new int []{1,2,3};
  try{
   for(int i = 0 ; i < k.length+1 ; i++ ){
    System.out.println(k[i]);
   }
   System.out.println("within a try block , so it is unreachable");
  }catch(Exception e){
   e.printStackTrace();
  }
  System.out.println("outside");
 }
}