java中实现递归计算二进制表示中1的个数

 /*use the recursive algorithme to calculate * the number of "1" in the binary expression * of an Integer N. * Note:if N is an odd, then * the result is the result of N/2 plus 1. * And the program use the bit operation to * improve efficency ,though it's seemingly * not necessary ,but the idea I think is good. * The program is writed by Zewang Zhang ,at * 2015-5-4,in SYSU dorms. */ public class CalculateNumberInBinaryExpression { //Main method. public static void main(String[] args) { //For example ,make N equals 13 ,the result shows 3 System.out.println(numOfEven(13)); //For example ,make N equals 128 ,the result shows 1 System.out.println(numOfEven(128)); } //The static method of numOfEven is the recursive method. public static int numOfEven(int x) { //The base of recursive. if(x==0) { return 0; } //If x is an odd. else if(x%2!=0) { return numOfEven(x>>1)+1; } //If x is an even except 0. else { while(x%2==0) { x=(x>>1); } return numOfEven(x); } } } 

 public int a(int i){ if(i==0||i==1) return i; return i%2+a(i/2); }