public static String getString(String s){
        String str = "" ;
        if(s!=null){
        for (int i = 0; i < s.length(); i++) {
            int  j = s.length() ;
            if(i==0){
                str = str+s.substring(j) ;
            }else{
                str = str+s.substring(j-i,j-i+1) ;
            }
            
        }
        str = str + s.substring(0, 1) ;
        }
        return str ;
    }
    
    public static void main(String[] args) throws Exception {
         String str = "abcdefg";
          int pos = 3;
     String s = str.substring(0, pos) ;
     String s2 = str.substring( pos+1) ;
     System.out.println(getString(s) + str.substring(pos, pos+1) +getString(s2));
    }

------解决方案--------------------
Java code


public class TestFrame{
    public static String reverseCell(String data){
        StringBuffer sb = new StringBuffer();
        for(int i=data.length()-1;i>=0;i--){
            sb.append(data.charAt(i));
        }
        return sb.toString();
    }
    public static String reverseAll(String str,int pos){
        if(str==null||str.length() == 0){
            return str;
        }
        StringBuffer sb = new StringBuffer();
        String temp = "";
        for(int i = 0;i <(str.length()-1)/3 + 1;i++){
            if(3*(i+1) < str.length()){
                temp = reverseCell(str.substring(3*i, 3*(i+1)));
            }
            else{
                temp = reverseCell(str.substring(3*i, str.length()));
            }
            sb.append(temp);
        }
        System.out.print(sb);
        return sb.toString();
    }
    public static void main(String args[]){
        String str="abcdefg";int pos = 3;
        reverseAll(str,pos);
    }
}