Simple, basic Bloom filter simulation in Java that uses multiple hash functions to efficiently test if an element might be in a set.

BloomFilter.java

package org.rakeshopensource.systemdesign;

import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
import java.util.function.Function;

public class BloomFilter <T> {
    private final int size;
    private final BitSet bitSet;
    private final List<Function<T, Integer>> hashFunctions;
    public BloomFilter(int size, List<Function<T, Integer>> hashFunctions) {
        this.size = size;
        this.bitSet = new BitSet(this.size);
        this.hashFunctions = hashFunctions;
    }

    public void add(T element){
        for(Function<T,Integer> hashFunction : hashFunctions){
            int hash = Math.abs(hashFunction.apply(element)) % size;
            bitSet.set(hash);

        }
    }

    public boolean mightContain(T element){
        for(Function<T,Integer> hashFunction : hashFunctions){
            int hash =  Math.abs(hashFunction.apply(element)) % size;
            if(!bitSet.get(hash)){
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {

        List<Function<String,Integer>> hashFunctions = new ArrayList<Function<String,Integer>>();

        //Function<String, Integer> fun2 = str -> str.hashCode();
        Function<String, Integer> fun1 = String::hashCode;
        Function<String, Integer> fun2 = String::length;
        Function<String, Integer> fun3 = (str) -> str.hashCode() * 31;

        hashFunctions.add(fun1);
        hashFunctions.add(fun2);
        hashFunctions.add(fun3);

        BloomFilter<String> bloomFilter = new BloomFilter<String>(640, hashFunctions);
        bloomFilter.add("apple");
        System.out.println(bloomFilter.mightContain("apple"));
        System.out.println(bloomFilter.mightContain("banana"));
    }
}