集合的hashCode方法的最佳实现

public int hashCode() {
   int result = 1;
   result = 31 * result + this.getMember(0);
   result = 31 * result + this.getMember(1);
   // 这里添加其他成员的哈希值，如果存在
   return result;
}

import org.apache.commons.collections.HashFunction;
import org.apache.commons.collections.function.Function;

import java.io.Serializable;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;

public class MyHashSet<E> extends HashSet<E> implements Serializable {
    private static final long serialVersionUID = 0L;
    private static final Object NULL_KEY = new Object(); // 用于空键的哈希值的特殊值
    
    private final HashFunction<Object> hashFunction;

    private MyHashSet (HashFunction<Object> hashFunction) {
        this.hashFunction = hashFunction;
    }
    
    public boolean add(E e) {
        if (insert(e, size() - 1)) {
            return true;
        }
        return false;
    }
    
    private boolean insert(E elem, int index) {
        int hashCode = hashFunction.hash(elem.getClass())
             + hashFunction.hash(elem.hashCode())
             + hashFunction.hash(NULL_KEY)
             + index;
        Object bucket = hashtable[hashCode % hashtable.length];

        if (bucket == NULL_KEY) {
            hashtable[hashCode % hashtable.length] = elem;
            return true;
        }

        Object prevObj = bucket;
        do {
            bucket = hashtable[hashCode % hashtable.length];
            Object existingObj = bucket;
            if (prevObj != existingObj) {
                prevObj = existingObj;
                while (prevObj != NULL_KEY && prevObj != existingObj) {
                    prevObj = bucket;
                    bucket = hashtable[hashCode % hashtable.length];
                }

                if (prevObj == NULL_KEY) {
                    hashtable[hashCode % hashtable.length] = elem;
                    return true;
                }

                if (hashFunction.equals(prevObj, existingObj))
                    return false;
                
                hashtable[hashCode % hashtable.length] = elem;
            } 
        } while (prevObj != bucket);
        
        return false;
    }
    
    public boolean remove(Object elem) {
        if (hashtable == null) return false;

        int hashCode = hashFunction
                .hash(elem.getClass())
                + hashFunction.hash(elem.hashCode());
        Object bucket = hashtable[hashCode % hashtable
                .length];

        while (bucket != NULL_KEY && bucket != elem) {
            bucket = hashtable[hashCode % hashtable
                    .length];
        }

        if (bucket == elem) {
            removeElement(elem.hashCode());
            return true;
        }

        return false;
    }
}