Codewar - Bit Counting

Write a function that takes an (unsigned) integer as input, and returns the number of bits that are equal to one in the binary representation of that number.

Example: The binary representation of 1234 is 10011010010, so the function should return 5 in this case.

package poj;
public class BitCounting {

	public static int countBits(int n){
		String binaryStr = Integer.toBinaryString(n);
		int count = 0;
		for(int i=0; i<binaryStr.length(); ++i){
			if(binaryStr.charAt(i) == '1'){
				count++;
			}
		}
		return count;
	}
}

package poj;
import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;


public class BitCountingTest {
  @Test
  public void testGame() {
    assertEquals(5, BitCounting.countBits(1234)); 
    assertEquals(1, BitCounting.countBits(4)); 
    assertEquals(3, BitCounting.countBits(7)); 
    assertEquals(2, BitCounting.countBits(9)); 
    assertEquals(2, BitCounting.countBits(10)); 
  }
}