An Introduction to Bit Operations, Masking and Filtering

BitFilteringTester.java

public class BitFilteringTester {
     
	InteractingObject a = new InteractingObject('a');
	InteractingObject b = new InteractingObject('b');
	InteractingObject c = new InteractingObject('c');
	InteractingObject d = new InteractingObject('d');
	InteractingObject e = new InteractingObject('e');
	InteractingObject f = new InteractingObject('f');
	
	public BitFilteringTester() {
		a.filter.category = InteractingObject.TYPE_A;
		a.filter.maskBits = InteractingObject.TYPE_B;
		
		b.filter.category = InteractingObject.TYPE_B;
		b.filter.maskBits = InteractingObject.TYPE_A;
		
		c.filter.category = InteractingObject.TYPE_C;
		c.filter.maskBits = InteractingObject.TYPE_A | InteractingObject.TYPE_B | InteractingObject.TYPE_C;
		
		d.filter.category = InteractingObject.TYPE_D;
		d.filter.maskBits = InteractingObject.TYPE_D;
		
		e.filter.category = InteractingObject.TYPE_E;
		e.filter.maskBits = 0;
	}
	
	public void runTest() {
		interactAll(a);
		interactAll(b);
		interactAll(c);
		interactAll(d);
		interactAll(e);
		interactAll(f);
	}
	
	
	public void interactAll(InteractingObject o) {
		interact(o, a);
		interact(o, b);
		interact(o, c);
		interact(o, d);
		interact(o, e);
		interact(o, f);
		System.out.println();
	}
    
	public void interact(InteractingObject o1, InteractingObject o2) {
		Filter f1 = o1.filter;
		Filter f2 = o2.filter;
		if(((f1.category & f2.maskBits) != 0) && ((f2.category & f1.maskBits) != 0)) {
			System.out.printf("%s and %s interacted.\n", o1.data, o2.data);
		} else {
			System.out.printf("%s and %s did not interact.\n", o1.data, o2.data);
		}
	}
	
    public static void main(String[] args) {
		BitFilteringTester tester = new BitFilteringTester();
		tester.runTest();
    }
	
	class InteractingObject {
		
		public static final int TYPE_A = 1 << 1;
		public static final int TYPE_B = 1 << 2;
		public static final int TYPE_C = 1 << 3;
		public static final int TYPE_D = 1 << 4;
		public static final int TYPE_E = 1 << 5;
		
		public Filter filter;
		public char data;
		
		public InteractingObject(char data) {
			this.data = data;
			this.filter = new Filter();
		}
	}
	
    class Filter {
        public int category = 1<<0;
        public int maskBits = ~0;
    }
     
}

BitMaskingTester.java

public class BitMaskingTester {
     
     public static final byte EXCLUSIVE              = 0;
     public static final byte INCLUDE_LEFT_ENDPOINT  = 1<<0;
     public static final byte INCLUDE_RIGHT_ENDPOINT = 1<<1;
     
     public static void main(String []args){
        testInterval(3, 2, 5);
        testInterval(2, 2, 5);
        testInterval(5, 2, 5);
        testInterval(1, 2, 5);
        testInterval(6, 2, 5);
     }
     
     public static void testInterval(int n, int min, int max) {
        System.out.printf("%d on interval (%d, %d): %b\n", n, min, max, isOnInterval(n, min, max, EXCLUSIVE));
        System.out.printf("%d on interval [%d, %d): %b\n", n, min, max, isOnInterval(n, min, max, INCLUDE_LEFT_ENDPOINT));
        System.out.printf("%d on interval (%d, %d]: %b\n", n, min, max, isOnInterval(n, min, max, INCLUDE_RIGHT_ENDPOINT));
        System.out.printf("%d on interval [%d, %d]: %b\n", n, min, max, isOnInterval(n, min, max, INCLUDE_LEFT_ENDPOINT | INCLUDE_RIGHT_ENDPOINT));
        System.out.println();
     }
 
    public static boolean isOnInterval(int n, int min, int max, int options) {
        boolean greaterThanMin;
        if((INCLUDE_LEFT_ENDPOINT & options) != 0) {
            greaterThanMin = n >= min;
        } else {
            greaterThanMin = n > min;
        }
        boolean lessThanMax;
        if((INCLUDE_RIGHT_ENDPOINT & options) != 0) {
            lessThanMax = n <= max;
        } else {
            lessThanMax = n < max;
        }
        return greaterThanMin && lessThanMax;
    }
     
}