mysql布隆过滤器源码_布隆过滤器（Bloom Filter）Java实现

import java.util.BitSet;

/**

*

* @author xkey

*/

public class BloomFilter {

private static final int DEFAULT_SIZE = 2 << 24;//布隆过滤器的比特长度

private static final int[] seeds = {3,5,7, 11, 13, 31, 37, 61};//这里要选取质数，能很好的降低错误率

private static BitSet bits = new BitSet(DEFAULT_SIZE);

private static SimpleHash[] func = new SimpleHash[seeds.length];

public static void addValue(String value)

{

for(SimpleHash f : func)//将字符串value哈希为8个或多个整数，然后在这些整数的bit上变为1

bits.set(f.hash(value),true);

}

public static void add(String value)

{

if(value != null) addValue(value);

}

public static boolean contains(String value)

{

if(value == null) return false;

boolean ret = true;

for(SimpleHash f : func)//这里其实没必要全部跑完，只要一次ret==false那么就不包含这个字符串

ret = ret && bits.get(f.hash(value));

return ret;

}

public static void main(String[] args) {

String value = "[email protected]";

for (int i = 0; i < seeds.length; i++) {

func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]);

}

add(value);

System.out.println(contains(value));

}

}

class SimpleHash {//这玩意相当于C++中的结构体

private int cap;

private int seed;

public SimpleHash(int cap, int seed) {

this.cap = cap;

this.seed = seed;

}

public int hash(String value) {//字符串哈希，选取好的哈希函数很重要

int result = 0;

int len = value.length();

for (int i = 0; i < len; i++) {

result = seed * result + value.charAt(i);

}

return (cap - 1) & result;

}

}

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2014-08-21 21:38

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