算法--字符串移位问题

import java.util.*;

public class Translation {

    public String stringTranslation(String A, int n, int len) {

        String str1 = reverseStr(A.toCharArray(),0,len-1);

        String str2 = reverseStr(A.toCharArray(),len,A.length()-1);

        return reverseStr((str1+str2).toCharArray(),0,n-1);    

    }

    public String reverseStr(char[] ch, int preIndex, int postfixIndex){

        StringBuilder sb = new StringBuilder();

        for(int i=postfixIndex; i>=preIndex; i--){

            sb.append(ch[i]);

        }

        return sb.toString();

    }

}