Java求一个数的二进制数中有几个1

第一种方法：循环，按位与上每一位（效率低）

import java.util.Scanner;

public class TextOne {
	public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int count = 0;
        for (int i = 0; i < 32; i++) {
            if (((n >> i) & 1) == 1) {
                count++;
            }
        }
        System.out.println("count:"+count);
    }  
}

第二种方法，按位与上（n-1），效率较高

import java.util.Scanner;

public class TextOne {
	public static void main (String[]args){
            Scanner scanner = new Scanner(System.in);
            int n = scanner.nextInt();
            int count = 0;
            while (n != 0) {
                n = n & (n - 1);
                count++;
            }
            System.out.println("count:"+count);
     }
}