奇怪的出错信息,哪位高手给解答一下!!!!!

Question

class  SubStr{  
             
           public  static  String  sub(String  src,  int  num){  
                         
                       char[]  c  =  src.toCharArray();  
                       int  i  =  0,  n  =  0;  
                       for(  ;  n  <=  num;  i++){  
                                   if(c[i]  >  128)  
                                       n  +=  2;  
                                     
                                   else    
                                             n++;  
                                     
                                   if(n  ==  num)  
                                       return  new  String(c,  0,  i+1);  
                                   else  if(n  -  num  ==  1)  
                                       return  new  String(c,  0,  i);  
                       }//在这里提示缺少返回值!!!!!!!!!!!!!!不明白.  
                         
                         
           }              
           public  static  void  main(String[]  args){  
                         
                       System.out.println(sub("电脑a的dsfdfi",  6));  
                                                 
           }  
             
}

Answer 1

if(n  ==  num)  
return  new  String(c,  0,  i+1);  
else  if(n  -  num  ==  1)  
return  new  String(c,  0,  i);
else ......    少了个else

Answer 2

一楼说个解决方法呀！！！
to二楼，我加上else还是不行啊！！！

Answer 3

class  SubStr{  
             
           public  static  String  sub(String  src,  int  num){  
                         
                       char[]  c  =  src.toCharArray();  
                       int  i  =  0,  n  =  0;  
                       String szRet = null;
                       for(  ;  n  <=  num;  i++){  
                                   if(c[i]  >  128)  
                                       n  +=  2;  
                                     
                                   else    
                                             n++;  
                                     
                                   if(n  ==  num)  
                                       szRet =  new  String(c,  0,  i+1);  
                                   else  if(n  -  num  ==  1)  
                                       szRet =  new  String(c,  0,  i);  
                       }
                       
                       return szRet; 
                         
           }              
           public  static  void  main(String[]  args){  
                         
                       System.out.println(sub("电脑a的dsfdfi",  6));  
                                                 
           }  
             
}

Answer 4

当然缺了，如果for一次也没有循环，就不能执行for里边的return了，所以for外边应该加个return。虽然有的时候for是一定会执行的，可是编译器可不知道。