布隆过滤器（Bloom Filter）的java实现

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Hash Function:

哈希函数就是将任意长度的数据转变成固定长度的数据（http://en.wikipedia.org/wiki/Hash_function）

Bloom Filter:

用java实现的Bloom Filter的代码如下

import java.util.BitSet;public class BloomFilter {private static final int DEFAULT_SIZE = 2 << 24;// Set DEFAULT_SIZE as 2^24 private static final int[] seed = new int[] {5, 7, 11, 13, 31, 37, 61};private BitSet bits = new BitSet(DEFAULT_SIZE);private SimpleHash[] func = new SimpleHash[seed.length];public BloomFilter() {for (int i = 0; i < seed.length; i++) {func[i] = new SimpleHash(DEFAULT_SIZE, seed[i]);}}public void add(String value) {for (SimpleHash f : func) bits.set(f.hash(value), true);}public boolean contains(String value) {if (value == null) return false;boolean rslt = true;for (SimpleHash f : func) {rslt = rslt & bits.get(f.hash(value));}return rslt;}public static class SimpleHash{private int cap;private int seed;SimpleHash(int cap, int seed){this.cap = cap;this.seed = seed;}public int hash(String value){int result = 0;int len = value.length();for (int i = 0; i < len; i++)result = result * seed + value.charAt(i);return (cap -1) & result;}}}

测试程序代码如下：

public class TestBloomFilter{public static void main(String[] args) {BloomFilter bf =new BloomFilter();bf.add("www.baidu.com");bf.add("www.sohu.com");bf.add("www.163.com");if(bf.contains("www.cctv.com"))System.out.println("www.cctv.com is in the set");elseSystem.out.println("www.cctv.com is not in the set");if(bf.contains("www.baidu.com"))System.out.println("www.baidu.com is in the set");elseSystem.out.println("www.baidu.com is not in the set");}}

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