Output an integer in binary representation

Problem description: Enter an integer and output the number of 1s in the binary representation of the number. Negative numbers are represented by complements.

Idea: Obviously, you can convert a decimal integer to a binary representation string, and then count the number of "1". Of course, it can also be solved by combining the division operation and the remainder operation.

Code:

import org.junit.Test;

public class NumberOf1 {
	public int numberOf1(int n) {
		String num = Integer.toBinaryString(n);
		System.out.println(num);//十进制n的二进制字符串表示
		int count = 0;
		for(int i = 0;i < num.length();i++)
			if(num.charAt(i)=='1')
				count++;
		return count;
    }
	@Test
	public void test(){
		System.out.println(numberOf1(15));
	}
}

Output:

1111
4