/*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);}