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Copy pathBloomFilter.java
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190 lines (161 loc) · 5.31 KB
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package src.main.java.com.search;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;
/**
* A simple implementation of Bloom filter.
* <p>
* Bloom filter have a chance of being wrong.
* <p>
* The Bloom filter assert that elements that do not exist must not exist,
* if assert an element exists, but not necessarily.
* <p>
* The accuracy rate depends on capacity and hash functions.
*
* @author yangxf
*/
public class BloomFilter implements Serializable {
private static final long serialVersionUID = -4466610350741278658L;
private static final int LONG_SHIFT = 6;
private static final int LONG_MASK = 63;
/**
* hash functions
*/
private final List<Function<String, Integer>> hashFunctions;
private final long[] table;
private final int tableMask;
private int size;
/**
* @param capacity the filter capacity
* @param hashFunctions hash functions
* @see Builder must be build by {@link Builder}.
*/
private BloomFilter(int capacity, List<Function<String, Integer>> hashFunctions) {
this.hashFunctions = hashFunctions;
int cap = nextPowerOf2(capacity);
tableMask = (cap << LONG_SHIFT) - 1;
table = new long[cap];
}
public static Builder builder(int capacity) {
if (capacity < 1) {
throw new IllegalStateException("capacity must be > 0");
}
return new Builder(capacity);
}
/**
* Add an element to the Bloom filter.
*/
public void add(String element) {
checkNotNull(element, "element");
for (Function<String, Integer> hashFunction : hashFunctions) {
int key = hashFunction.apply(element) & tableMask;
table[key >>> LONG_SHIFT] |= (1 << (key & LONG_MASK));
}
size++;
}
/**
* @return true if the element exists, otherwise false.
*/
public boolean contains(String element) {
if (element == null) {
return false;
}
for (Function<String, Integer> hashFunction : hashFunctions) {
int key = hashFunction.apply(element) & tableMask;
if ((table[key >>> LONG_SHIFT] & (1 << (key & LONG_MASK))) == 0) {
return false;
}
}
return true;
}
public List<Function<String, Integer>> getHashFunctions() {
return hashFunctions;
}
public int size() {
return size;
}
private static void checkNotNull(String element, String msg) {
if (element == null) {
throw new NullPointerException(msg + " must be not null");
}
}
private static int nextPowerOf2(int i) {
int n = i - 1;
n |= n >>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n < 0) ? 1 : (n >= 0x40000000) ? 0x40000000 : n + 1;
}
/**
* We need a list of unmodifiable hash functions.
*/
public static class Builder {
private int capacity;
private List<Function<String, Integer>> hashFunctions = new ArrayList<>();
private Builder(int capacity) {
this.capacity = capacity;
}
public Builder addHashFunction(Function<String, Integer> function) {
hashFunctions.add(function);
return this;
}
public BloomFilter build() {
if (hashFunctions.isEmpty()) {
addDefaultHashFunction();
}
return new BloomFilter(capacity, Collections.unmodifiableList(hashFunctions));
}
/**
* I provides several default hash functions
*/
private void addDefaultHashFunction() {
// Java String Hash Function
hashFunctions.add(String::hashCode);
// SDBM Hash Function
hashFunctions.add(key -> {
if (key == null || key.isEmpty()) {
return 0;
}
int hash = 0;
for (int i = 0; i < key.length(); i++) {
hash = key.charAt(i) + (hash << 6) + (hash << 16) - hash;
}
hash &= 0x7ffffff;
return hash;
});
// Robert Sedgwicks Hash Function
hashFunctions.add(key -> {
if (key == null || key.isEmpty()) {
return 0;
}
int hash = 0;
int magic = 63689;
for (int i = 0; i < key.length(); i++) {
hash = hash * magic + key.charAt(i);
magic *= 378551;
}
return hash;
});
// Arash Partow Hash Function
hashFunctions.add(key -> {
if (key == null || key.isEmpty()) {
return 0;
}
int hash = 0;
for (int i = 0; i < key.length(); i++) {
char ch = key.charAt(i);
if ((i & 1) == 0) {
hash ^= ((hash << 7) ^ ch ^ (hash >> 3));
} else {
hash ^= (~((hash << 11) ^ ch ^ (hash >> 5)));
}
}
return hash;
});
}
}
}