布隆过滤

布隆过滤的简单实现

public class BloomFilterTest {
	
	public static void main(String[] args) {
		
		BloomFilter bloomFilter = new BloomFilter();
		bloomFilter.addElement("zhou");
		bloomFilter.addElement("yu");
		
		System.out.println(bloomFilter.containElement("zhou"));
		System.out.println(bloomFilter.containElement("li"));
	}
	
}

class BloomFilter {
	// 容量
	private static final int DEFAULT_SIZE = 1 << 20;
	
	// 位数组
	private BitSet sets = new BitSet(DEFAULT_SIZE);
	
	/**
	 * 添加元素
	 */
	public void addElement(Object obj) {
		sets.set(hash1(obj), true);
		sets.set(hash2(obj), true);
	}
	
	/**
	 * 判断是否存在
	 * @param obj
	 * @return
	 */
	public boolean containElement(Object obj) {
		return sets.get(hash1(obj)) && sets.get(hash2(obj));
	}
	
	/**
	 * 对hashcold进行扰动，然后根据容量取余
	 */
	private int hash1(Object obj) {
		return hash(obj, 3);
	}
	
	/**
	 * 对hashcold进行扰动，然后根据容量取余
	 */
	private int hash2(Object obj) {
		return hash(obj, 16);
	}
	
	private int hash(Object obj, int seed) {
		int h;
		return (obj == null) ? 0 : (DEFAULT_SIZE - 1) & ((h = obj.hashCode()) ^ (h >>> seed));
	}
}