几种方法的尾递归实现

http://freejvm.iteye.com/blog/976878

需要找时间验证一下，另外还需要学习多个参数的尾递归如何来实现的技巧

斐波那契数列第n个数的求值，

 public static long fibo4(int n)
        {
            if (n < 2)
            {
                return n - 1;
            }
            else
            {
                return fibo4Helper(n, 0, 1, 3); //保持与非尾递归接口不变，是借助帮助方法实现尾递归的
            }
        }
        private static long fibo4Helper(int n, long prepre, long pre, int begin)
        {
            if (n == begin)
            {
                return pre + prepre;
            }
            else
            {
                return fibo4Helper(n, pre, prepre + pre, ++begin);    //这里相当于迭代实现for-loop的浓缩
            }
        }   

//----------------------尾递归的其他实现-------------------------------------->
    //2. 求最大公约数
    public static int gcd(int big,int small){
        if(big%small==0) return small;
        return gcd(small, big%small);
    }
    //3.1 阶乘--非尾递归
    public static int fn1(int n){
        if(n<2) return 1;
        return n*fn1(n-1);
    }
    //3.2 阶乘--尾递归
    public static int fn2(int n){
        if(n<2) return 1;
        return fn2Helper(1, n);
    }
    private static int fn2Helper(int ret, int n){
        if(n<2) return ret;
        return fn2Helper(ret*n,n-1);
    }
        //4.1 翻转字符串--非尾递归
       public static String reverse1(String s, int length){
            if(length==0) return ""; //下一行的"+"可借助高版本JDK编译器的优化
            return s.charAt(length-1)+reverse1(s,length-1);
        }
       //4.2 翻转字符串--尾递归
       public static String reverse2(String s){
           return reverse2Helper(s, "", s.length());
       }
       private static String reverse2Helper(String s,String init,int len){
           if(len==0) return init;
           return reverse2Helper(s, init+s.charAt(len-1), len-1);
       }
    //5. 验证字符串是否是回文 testHuiwen("abcdcba")
     public static boolean testHuiwen(String s){
         return testHuiwenHelper(s, 0, s.length());
     }
     private static boolean testHuiwenHelper(String s,int begin, int len){
         if(begin< len>>1 && s.charAt(begin)==s.charAt(len-begin-1))
             return testHuiwenHelper(s, begin+1, len);
         else if(begin==len>>1) return true;
         else return false;
     }
    //6. 翻转整数 如:1024=>4201
     public static int reverseInt(int i){
         return reverseIntHelper(i, 0);
     }
     private static int reverseIntHelper(int i, int init){
         if(i==0) return init;
         return reverseIntHelper(i/10, init*10+i%10);
     }
}