手写hashMap

/***

• 手写hashmap

• @param

• @param
  */
  public class MbHMap<K, V> implements MbMap<K, V> {

  public static int defultLength = 16;

  //定义一个HashMap骨架数组
  public Entry<K, V>[] table = null;

  //扩容标准 数组总长度/以使用数组长度
  private static double defultAddSizeFactor = 0.75;
  //以使用的数组
  private int userSize;

  public MbHMap() {
  this(defultLength, defultAddSizeFactor);
  }

  //数组长度 ，扩容标准
  public MbHMap(int length, double defultAddSizeFactor) {
  if (length < 0) {
  throw new IllegalArgumentException(“数组参数不能为负数”);
  }

   if (defultAddSizeFactor <= 0 || Double.isNaN(defultAddSizeFactor)) {
       throw new IllegalArgumentException("扩容标注必须大于0");
   }
  
   this.defultLength = length;
   this.defultAddSizeFactor = defultAddSizeFactor;
   table = new Entry[length];
  

  }

  /***

  • 快速存储

  • @param k

  • @param v

  • @return
    */
    public V put(K k, V v) {
    if (userSize > defultAddSizeFactor * defultLength) {
    //扩容
    up2Size();
    }
    //通过key来找到存储位置
    int index = getIndex(k, table.length);
    //拿到对应entry值
    Entry<K, V> entry = table[index];

    if (entry == null) {
    table[index] = new Entry(k, v, null);
    userSize++;
    } else { //Entry有值时
    table[index] = new Entry(k, v, entry);
    }
    return entry.getValue();
    }

  //扩容2倍
  private void up2Size() {
  // 16 * 2
  Entry<K, V>[] newTable = new Entry[2 * defultLength];

   //将散列的数组再次散列
   againHash(newTable);
  

  }

  private void againHash(Entry<K, V>[] newTable) {
  //将数组对象封装List
  List<Entry<K, V>> entrylist = new ArrayList<Entry<K, V>>();

   for (int i = 0; i < table.length; i++) {
       if (table[i] == null) {
           continue;
       }
  
       fundEntryByNext(table[i], entrylist);
   }
  
   if (entrylist.size() > 0) {
       userSize = 0;
       defultLength = 2 * defultLength;
       table = newTable;
       //将最上面一个entry对象 next情况
       for (Entry<K, V> entry : entrylist) {
           if (entry.next != null) {
               entry.next = null;
           }
  
           put(entry.getKey(), entry.getValue());
       }
   }
  

  }

  //根据entry 选择下一个entry
  private void fundEntryByNext(Entry<K, V> entry, List<Entry<K, V>> entrylist) {
  if (entry != null && entry.next != null) {
  entrylist.add(entry);
  //递归加集合中
  fundEntryByNext(entry.next, entrylist);
  } else {
  entrylist.add(entry);
  }

  }

  //通过数组长度 ，和k的位置 来找到Entry 存放位置
  public int getIndex(K k, int length) {

   int m = length - 1;
   int index = hash(k.hashCode()) & m;
   //三木运算符保证数据正确
   return index >= 0 ? index : -index;
  

  }

  //找到自己的Hash算法
  private int hash(int hashCode) {
  hashCode = hashCode ^ ((hashCode >>> 20)) ^ (hashCode >>> 12);

   return hashCode ^ ((hashCode >>> 7)) ^ (hashCode >>> 4);
  

  }

  /***

  • 快取

  • @param k

  • @return
    */
    @Override
    public V get(K k) {

    int index = getIndex(k, table.length);
    if (table[index] == null) {
    throw new NullPointerException(“空指针异常”);
    }

    return findValueByEqualKey(k, table[index]);
    }

  /**

  • 通过key找到实体对象

  • @param k

  • @param entry

  • @return
    */
    private V findValueByEqualKey(K k, Entry<K, V> entry) {

    if (k == entry.getKey() || k.equals(entry.getKey())) {
    return entry.getValue();
    } else if (entry.next != null) {
    return findValueByEqualKey(k, entry.next);
    }

    return null;
    }

  /**

  • 内部类

  • @param

  • @param
    */
    class Entry<K, V> implements MbMap.Entry<K, V> {

    K k;
    V v;
    Entry<K, V> next; //指向被this积压的entry对象

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

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

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

  }

  public int userSize() {
  return userSize;
  }

  public static int getDefultLength() {
  return defultLength;
  }

  public static void setDefultLength(int defultLength) {
  MbHMap.defultLength = defultLength;
  }

  public Entry<K, V>[] getTable() {
  return table;
  }

  public void setTable(Entry<K, V>[] table) {
  this.table = table;
  }

  public static double getDefultAddSizeFactor() {
  return defultAddSizeFactor;
  }

  public static void setDefultAddSizeFactor(double defultAddSizeFactor) {
  MbHMap.defultAddSizeFactor = defultAddSizeFactor;
  }

  public int getUserSize() {
  return userSize;
  }

  public void setUserSize(int userSize) {
  this.userSize = userSize;
  }
  }