HashTable.java

import java.util.*;

class HashTable<K, V> {
    private ArrayList<HashNode<K, V> > bucketArray;
    private int numBuckets;
    private int size;
    public HashTable() {
        bucketArray = new ArrayList<>();
        numBuckets = 10;
        size = 0;
        for (int i = 0; i < numBuckets; i++)
            bucketArray.add(null);
    }
    public int size() { return size; }
    public boolean isEmpty() { return size() == 0; }
    private int hashCode (K key) {
            int hash = 7;
            hash = 31 * hash + (int) Double.parseDouble(key.toString());
            hash = 31 * hash + (int) Double.parseDouble(key.toString());
            hash = 31 * hash + (int) Double.parseDouble(key.toString());
            return hash;
    }

    private int getBucketIndex(K key) {
        int hashCode = hashCode(key);
        int index = hashCode % numBuckets;
        // key.hashCode() could be negative.
        index = index < 0 ? index * -1 : index;
        return index;
    }

    public void get(K key) {
        int bucketIndex = getBucketIndex(key);
        int hashCode = hashCode(key);

        HashNode<K, V> head = bucketArray.get(bucketIndex);
        while (head != null) {
            if (head.key.equals(key) && head.hashCode == hashCode)
                return;
            head = head.next;
        }
    }

    public void add(K key, V value) {
        int bucketIndex = getBucketIndex(key);
        int hashCode = hashCode(key);
        HashNode<K, V> head = bucketArray.get(bucketIndex);
        while (head != null) {
            if (head.key.equals(key) && head.hashCode == hashCode) {
                head.value = value;
                return;
            }
            head = head.next;
        }
        size++;
        head = bucketArray.get(bucketIndex);
        HashNode<K, V> newNode = new HashNode<>(key, value, hashCode);
        newNode.next = head;
        bucketArray.set(bucketIndex, newNode);
        if ((1.0 * size) / numBuckets >= 0.7) {
            ArrayList<HashNode<K, V> > temp = bucketArray;
            bucketArray = new ArrayList<>();
            numBuckets = 2 * numBuckets;
            size = 0;
            for (int i = 0; i < numBuckets; i++)
                bucketArray.add(null);
            for (HashNode<K, V> headNode : temp) {
                while (headNode != null) {
                    add(headNode.key, headNode.value);
                    headNode = headNode.next;
                }
            }
        }
    }
}