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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