BloomFilter.java

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.BitSet;
import java.util.Random;

public class BloomFilter<E> {
    private BitSet bf;
    private int bitArraySize;
    private int numHashFunc;

    public BloomFilter(int bitArraySize, int numHashFunc) {
        this.bitArraySize = bitArraySize;
        this.numHashFunc = numHashFunc;
        bf = new BitSet(bitArraySize);
    }

    public BloomFilter() {
        this(100000000, 6);
    }

    public void add(E obj) {
        int[] indexes = getHashIndexes(obj);
        for (int index : indexes) {
            bf.set(index);
        }
    }

    public boolean contains(E obj) {
        int[] indexes = getHashIndexes(obj);
        for (int index : indexes) {
            if (bf.get(index) == false) {
                return false;
            }
        }
        return true;
    }

    public void union(BloomFilter<E> other) {
        bf.or(other.bf);
    }

    protected int[] getHashIndexes(E obj) {
        int[] indexes = new int[numHashFunc];
        long seed = 0;
        byte[] digest;
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(obj.toString().getBytes());
            digest = md.digest();
            for (int i = 0; i < 6; i++) {
                seed = seed | (((long) digest[i] & 0xFF)) << (8 * i);
            }
        } catch (NoSuchAlgorithmException e) {
        }
        Random gen = new Random(seed);
        for (int i = 0; i < numHashFunc; i++) {
            indexes[i] = gen.nextInt(bitArraySize);
        }
        return indexes;
    }
}