迷你版HashMap

1:map父類

package jav.qq.mymap;

/**
 * 類描述:HashMap父類
 *
 * @author fengyong
 * @version 1.0
 * @since 1.0
 * Created by fengyong on 16/9/10 下午5:24.
 */
public class MyAbsMap {
    int hash(Object key) {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
    }

    int indexFor(int h, int length) {
        return h & (length-1);//二進制與運算,理論上運算完之後均勻分佈,並且比取餘運算速度快
   }
}

2:MyMap接口

package jav.qq.mymap;

/**
 * 類描述:
 *
 * @author fengyong
 * @version 1.0
 * @since 1.0
 * Created by fengyong on 16/9/10 下午4:21.
 */
public interface MyMap<K,V> {
    V put(K k,V v);
    V get(K k);
    int size();
    V remove(K k);
    interface Entry<K,V>{
    }
}

3:迷你版HashMap

package jav.qq.mymap;

/**
 * 類描述:參考java6,簡易HashMap
 *
 * @author fengyong
 * @version 1.0
 * @since 1.0
 * Created by fengyong on 16/9/10 下午4:23.
 */
public class MyHashMap<K, V> extends MyAbsMap implements MyMap<K, V> {

    //默認的容器大小
    static final int DEFAULT_INITIAL_CAPACITY = 16;
    //默認的負載因子
    static final float DEFAULT_LOAD_FACTOR = 0.75f;
    //集合中的個數
    private int size = 0;
    //容器大小
    private int capacity = 0;

    private float factor = DEFAULT_LOAD_FACTOR;
    //數組    數組中的對象中包含了next對象,爲鏈表
    private Node<K, V>[] tables = null;

    @Override
    public V put(K k, V v) {
        //如果tables爲空,創建
        if (null == tables)
            createDefTable();
        //如果k爲null
        if (null == k)
            return putNull(v);
        int hash = hash(k);
        addNode(hash, k, v, indexFor(hash, tables.length));
        return null;
    }

    @Override
    public V get(K k) {
        if (size == 0)
            return null;
        if (null == k)
            return getNull();
        return getNode(k);
    }

    @Override
    public int size() {
        return size;
    }

    @Override
    public V remove(K k) {
        if (size == 0)
            return null;
        int hash = hash(k);
        int index = indexFor(hash, tables.length);

        Node<K, V> node = tables[index];
        Node<K, V> e = node;

        while (e != null) {
            Node<K, V> next = e.next;

            if (hash == hash(e.key) && (k == e || (k != null && k.equals(e.key)))) {
                size--;
                if (e == node)
                    tables[index] = next;
                else
                    node.next = next;
                return e.value;
            }
            node = e;
            e = next;
        }
        return null;
    }
    //比較難理解的方法,擴容時調用
    private void createTable() {
        Node<K, V>[] newTables = new Node[tables.length * 2];
        for (Node<K, V> e : tables) {
            while (null != e) {
                Node<K, V> next = e.next;
                int index = indexFor(e.hash, newTables.length);
                e.next = newTables[index];//newTables[index]已經有數據,將原有的數據放在e的next中,再將e放到newTables[index]中,完成鏈表操作
                newTables[index] = e;
                e = next;//鏈表
            }
        }
        tables = newTables;
        capacity = tables.length;
    }
    private V getNode(K k) {
        int hash = hash(k);
        for (Node<K, V> e = tables[indexFor(hash, tables.length)]; e != null; e = e.next) {
            if (hash == hash(e.key) && (k == e.key || k.equals(e.key))) {
                return e.value;
            }
        }
        return null;
    }
    private V getNull() {
        for (Node<K, V> e = tables[0]; e != null; e = e.next) {
            if (e.key == null && e.hash == 0) {
                return e.value;
            }
        }
        return null;
    }
    private void createDefTable() {
        tables = new Node[DEFAULT_INITIAL_CAPACITY];
    }
    private V putNull(V v) {
        if (size >= (factor * tables.length))
            createTable();
        for (Node<K, V> e = tables[0]; e != null; e = e.next) {
            if (null == e.key) {
                V oldValue = e.value;
                e.value = v;
                return oldValue;
            }
        }
        addNode(0, null, v, 0);
        return null;
    }
    private void addNode(int hash, K k, V v, int index) {
        if (size >= (factor * tables.length))
            createTable();
        Node<K, V> node = tables[index];
        tables[index] = new Node(hash, k, v, node);
        size++;
    }
    class Node<K, V> implements MyMap.Entry<K, V> {

        int hash;
        K key;
        V value;
        Node<K, V> next;

        public Node(int hash, K key, V value, Node<K, V> next) {
            this.hash = hash;
            this.key = key;
            this.value = value;
            this.next = next;
        }
    }
}