HashTable.java

import java.util.TreeMap;

/**
 * Author : 13152
 * Date : 2020/2/7
 * Time : 17:12
 * Version ： 1.0.0
 **/
public class HashTable<K, V> {  // K不具有可比较性

    private final int[] capacity = {
            53, 97, 193, 389, 769, 1543, 3079, 6151, 12289, 24593,
            49157, 98317, 196613, 393241, 786433, 1572869, 3145739,
            6291469,12582917, 25165843, 50331653, 100663319, 201326611,
            402653189, 805306457, 1610612741
    };

    private static final int upperTol = 10;
    private static final int lowerTol = 2;
    private int capacityIndex = 0;
    private TreeMap<K, V>[] hashTable;
    private int M;
    private int size;

    public HashTable() {
        this.M = capacity[capacityIndex];
        size = 0;
        hashTable = new TreeMap[M];
        for (int i = 0; i < M; i++)
            hashTable[i] = new TreeMap<>();
    }

    private int hash(K key) {
        return (key.hashCode() & 0x7FFFFFFF) % M;
    }

    public int getSize() {
        return size;
    }

    public void add(K key, V value) {
        TreeMap<K, V>map = hashTable[hash(key)];
        if (map.containsKey(key))
            map.put(key, value);
        else{
            map.put(key, value);
            size++;
            if (size >= upperTol * M && capacityIndex + 1 < capacity.length) {
                capacityIndex++;
                resize(capacity[capacityIndex]);
            }
        }
    }

    public V remove(K key) {
        TreeMap<K, V> map = hashTable[hash(key)];
        if (map.containsKey(key)) {
            size--;
            if (size < lowerTol * M && capacityIndex - 1 >= 0){
                capacityIndex--;
                resize(capacity[capacityIndex]);
            }
            return map.remove(key);
        }
        return null;
    }

    public void set(K key, V value) {
        TreeMap<K, V> map = hashTable[hash(key)];
        if (map.containsKey(key))
            map.put(key, value);
    }

    public boolean contains(K key) {
        TreeMap<K, V> map = hashTable[hash(key)];
        return map.containsKey(key);
    }

    public V get(K key) {
        return hashTable[hash(key)].get(key);
    }

    private void resize(int newM) {

        TreeMap<K, V>[] newHashTable = new TreeMap[newM];
        for (int i = 0; i < newM; i++)
            newHashTable[i] = new TreeMap<>();

        int oldM = this.M;
        this.M = newM;
        for (int i = 0; i < oldM; i++) {
            TreeMap<K, V> map = hashTable[i];
            for (K key : map.keySet())
                newHashTable[hash(key)].put(key, map.get(key));
        }

        this.hashTable = newHashTable;
    }
}