手写HashMap

首先定义接口：

public interface VMap<K, V> {

    V put(K key, V value);

    V get(K key);

    Integer size();

    interface Entry<K, V> {

        K getKey();

        V getValue();
    }
}

实现接口：

import java.util.Arrays;

public class VHashMap<K, V> implements VMap<K, V> {

    //大小
    private Integer size = 0;
    //默认大小
    private Integer defaultLength = 16;
    //负载因子
    private double loadFactor = 0.75D;
    //存储数据的数组
    private Entry<K, V>[] table;

    VHashMap(Integer _defaultLength, double _loadFactor) {
        this.defaultLength = _defaultLength;
        this.loadFactor = _loadFactor;
        this.table = new Entry[defaultLength];
    }

    VHashMap() {
        this.table = new Entry[defaultLength];
    }

    Integer getIndex(K key) {
        return Math.abs((key.hashCode() % (defaultLength - 1)));
    }

    @Override
    public V put(K key, V value) {
        //获取下标
        Integer index = getIndex(key);
        //扩容
        if (table.length <= index + 1) {
            Integer len = table.length + (int) (table.length * loadFactor);
            Entry<K, V>[] newTable = Arrays.copyOf(table, len);
            this.table = newTable;
        }
        //判断下标是否被占用
        Entry<K, V> kvEntry = table[index];
        //没有被占用
        if (kvEntry == null) {
            table[index] = new Entry(key, value, null, index);
            size++;
        } else {
            //判断是否相同的key
            if (kvEntry.key.equals(key)) {
                //覆盖
                table[index] = new Entry(key, value, kvEntry.next, index);
            } else {
                //把新的值放进去
                table[index] = new Entry(key, value, kvEntry, index);
                size++;
            }
        }

        return table[index].getValue();
    }

    @Override
    public V get(K key) {
        Integer index = getIndex(key);
        Entry<K, V> kvEntry = table[index];
        do {
            if (kvEntry.key.equals(key)) {
                return table[index].getValue();
            }
            Entry<K, V> next = kvEntry.next;
            if (next == null) {
                return null;
            }
            kvEntry = kvEntry.next;
        } while (!key.equals(kvEntry.key));

        return kvEntry.getValue();
    }

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

    class Entry<K, V> implements VMap.Entry<K, V> {

        private Entry<K, V> next;
        private Integer index;
        private K key;
        private V value;

        Entry(K _key, V _value, Entry<K, V> _next, Integer _index) {
            this.key = _key;
            this.value = _value;
            this.next = _next;
            this.index = _index;
        }

        Entry() {
        }

        @Override
        public K getKey() {
            return this.key;
        }

        @Override
        public V getValue() {
            return this.value;
        }
    }
}