简单实现jdk1.7HashMap

news2024/11/19 2:38:22

1.定义一个Map接口,Entry<K,V>对象为Map的元素

package test;

public interface Map<K,V> {
    V put(K k,V v);
    V get(K k);
    int size();

    interface Entry<K,V>{
       K getKey();
       V getValue();
    }

}

2.主要实现了put,get以及size()方法

package test;


public class HashMap<K, V> implements Map<K, V> {
    Entry[] table = null;
    int size;

    HashMap() {
        table = new Entry[16];
    }

    /**
     * 1.hashCode(k),算出哈希值
     * 2.取余运算算出index索引值
     * 3.是否有值,如果没有值则添加,有值则添加到链表中
     *
     * @param k
     * @param v
     * @return
     */
    @Override
    public V put(K k, V v) {
        int index = hash(k);
        System.out.println(k.hashCode());
        if (table[index] == null) {
            table[index] = new Entry(k, v, k.hashCode(), null);
            size++;
        } else {
            table[index] = new Entry(k, v, k.hashCode(), table[index]);
        }
        return (V) table[index].getValue();
    }

    private int hash(K k) {
        int i = k.hashCode() % 16;
        return i > 0 ? i : Math.abs(i);
    }

    /**
     * 1.通过k获取到hashCode值
     * 2.算出index
     * 3.判断k是否相等,如果相等则返回,如果不等则判断其他链表是否相等
     *
     * @param k
     * @return
     */
    @Override
    public V get(K k) {
        int hash = hash(k);
        Entry<K, V> entry = table[hash];
        return findValueByKey(entry, k);
    }

    private V findValueByKey(Entry<K, V> entry, K k) {
        if (entry == null) {
            return null;
        }
        if (entry.getKey().equals(k) || k == entry.getKey()) {
            return (V) entry.getValue();
        } else if (entry.next != null) {
            return (V) findValueByKey(entry.next, k);
        }
        return null;
    }

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

    static class Entry<K, V> implements Map.Entry<K, V> {
        K k;
        V v;
        int hashCode;
        Entry<K, V> next;

        public Entry(K k, V v, int hashCode, Entry<K, V> next) {
            this.k = k;
            this.v = v;
            this.hashCode = hashCode;
            this.next = next;
        }

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

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

3.测试

package test;



public class test {
    public static void main(String[] args) {
        Map<String, Object> map = new HashMap<String,Object>();
        map.put("lzf", "海淀");
        map.put("zhx", "昌平");
        map.put("wq", "朝阳");
        int size = map.size();
        System.out.println(map.get("lzf"));
        System.out.println(map.get("zhx"));
        System.out.println(map.get("wq"));
        System.out.println("size = " + size);
    }
}

4.结果