布隆过滤器 (Bloom Filter) 详解
https://www.jianshu.com/p/28dd26aaf2ee
http://www.cnblogs.com/hitwtx/archive/2011/08/24/2152180.html
import java.util.BitSet;
public class SimpleBloomFilter {
private static final int DEFAULT_SIZE =2 << 24 ;
private static final int [] seeds =new int []{5,7, 11 , 13 , 31 , 37 , 61};
private BitSet bits= new BitSet(DEFAULT_SIZE);
private SimpleHash[] func=new SimpleHash[seeds.length];
public SimpleBloomFilter() {
for( int i= 0 ; i< seeds.length; i ++ ) {
func[i]=new SimpleHash(DEFAULT_SIZE, seeds[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 ret = true ;
for(SimpleHash f : func) {
ret=ret&& bits.get(f.hash(value));
}
return ret;
}
//内部类,simpleHash
public static class SimpleHash {
private int cap;
private int seed;
public 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 =seed* result + value.charAt(i);
}
return (cap - 1 ) & result;
}
}
public static void main(String[] args) {
String value = "[email protected]" ;
SimpleBloomFilter filter=new SimpleBloomFilter();
System.out.println(filter.contains(value));
filter.add(value);
System.out.println(filter.contains(value));
}
}