自己写一个Map

public class WhalesonMap<K,V> {

   Entry<K,V> [] tab;

   private int CAPACITY = 1 << 4;//6

   @AllArgsConstructor
   @NoArgsConstructor
   @Data
   public class Entry<K,V>{

       private K key;

       private V value;

       private Entry<K,V> next;

   }

   public void put(K key, V value){

       if(tab == null){
           initialize();
       }
       int keyHashCode = toHash( key );
       int index = indexFor(keyHashCode);

       for (Entry<K,V> entry = tab[index]; entry != null; entry = entry.next){
           if(entry.key.equals(key)){

               entry.key = key;
           }
       }
       addEntry(key,value,index);

   }

   public V get(K k){
       int hash = toHash(k);
       int index = indexFor(hash);
       Entry<K,V> tempEntry = tab[index];
       if(tempEntry == null){
           throw new NullPointerException("No exist k in tab");
       }
       return tempEntry.getValue();
   }

   private void addEntry(K key, V value, int index) {
       Entry<K,V> entry = new Entry<>(key,value,tab[index]);
       tab[index] = entry;
   }

   private int indexFor(int keyHashCode) {
       //也可以用数组长度取模
       return keyHashCode % tab.length ;
   }

   public void initialize(){
       tab = new Entry[CAPACITY];
   }

   public int toHash(K k){
       return k.hashCode();
   }
}