自己实现HashMap

/**
 * hashmap的demo
 * @author cuiyc
 * @version 1.0
 * @date 2021/6/5 22:28
 */
public class HashMapDemo {
    public static void main(String[] args) {

        Map<String,String> hashmap=new HashMap<>();

        MyHashMap map=new MyHashMap();
        map.put("k1","v1");
        map.put("k2","v2");
        System.out.println("map的长度是,"+map.size);
        System.out.println("k2的value是,"+map.get("k2"));
        System.out.println("k1的value是,"+map.get("k1"));
    }

    private static class MyHashMap{
        private int size;
        LinkedList[] array =new LinkedList[999];


        public MyHashMap(){}
        public MyHashMap(int size){
            this.size=size;
        }

        //计算key的hashcode值
        final int hash(Object key){
            int h;
            return (key==null)?0:(h=key.hashCode())^(h>>>16);
        }
        //对数组的长度取模，得到应该存入的位置
        final int mode(int h){
            return h/array.length;
        }

        //得到size的值
        public int getSize(){
            return size;
        }
        //put方法
        public void put(Object key,Object value){
            //先把key 和 value放入entry对象中
            MyEntry myEntry=new MyEntry(key,value);
            //根据key值计算出hashcode值，然后得到应当在数组中存放的位置
            int hashValue=hash(key);
            //然后拿到hahscode值后，再和数组的长度取模计算出再数组中的一个位置
            hashValue=mode(hashValue);
            //若该位置为空，则直接添加链表
            if(array[hashValue]==null){
                LinkedList linkedList=new LinkedList();
                linkedList.add(myEntry);
                array[hashValue]=linkedList;
            }else {
                //否则，该位置是已经相同的key值，则需要遍历到key值的entry，然后更新。
                for (int i = 0; i < array[hashValue].size(); i++) {
                     MyEntry myentry= (MyEntry) array[hashValue].get(i);
                     if(key.equals(myentry.getKey())){
                         myentry.value=value;
                     }else {
                         array[hashValue].add(myEntry);
                     }
                }
            }
            size++;
        }

        //get方法
        public Object get(Object Key){
            int hashCode=mode(Key.hashCode());
            if(array[hashCode]!=null){
                for (int i = 0; i < array[hashCode].size(); i++) {
                   MyEntry myEntry= (MyEntry) array[hashCode].get(i);
                   if(Key.equals(myEntry.getKey())){
                       return myEntry.value;
                   }
                }
            }
            return null;
        }
    }

    //Entry数据结构
    private static class MyEntry<K,V> implements Map.Entry<K,V>{
        int hash;
        final K key;
        V value;
        MyEntry<K,V> next;

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

        public MyEntry(K key,V value){
            this.key=key;this.value=value;
        }



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

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

        @Override
        public V setValue(V newValue) {
            V oldValue=value;
            value=newValue;
            return oldValue;
        }

        @Override
        public final boolean equals(Object o) {
            if (o == this){
                return true;
            }
            if (o instanceof Map.Entry) {
                Map.Entry<?,?> e = (Map.Entry<?,?>)o;
                if (Objects.equals(key, e.getKey()) &&
                        Objects.equals(value, e.getValue())){
                    return true;
                }
            }
            return false;
        }

        @Override
        public final int hashCode() {
            return Objects.hashCode(key) ^ Objects.hashCode(value);
        }


    }
}