Count 1's in a number.

BitCounter.java

public class BitCounter {
    public static void main(final String... args) {
        int i = Integer.parseInt(args[0]);
        int m = Integer.parseInt(args[1]);
        int count = 0;
        switch (m) {
	case 0:
	    // iterates 32 regarless of the value
	    for (int j = 0; j < Integer.SIZE; j++) {
		if ((i & 0x01) == 0x01) {
		    count++;
		}
		i >>>= 1;
	    }
	    break;
	case 1:
	    // iterates for only the number of 1s
	    for (; i > 0; count++) {
		i &= i - 1;
	    }
	    break;
	default:
	    // java.lang.Integer#bitCount(i)
	    i = i - ((i >>> 1) & 0x55555555);
	    i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
	    i = (i + (i >>> 4)) & 0x0f0f0f0f;
	    i = i + (i >>> 8);
	    i = i + (i >>> 16);
	    count = i & 0x3f;
	    break;
        }
        System.out.println(count);
    }
}