HashTable源码分析

/**

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• The hash table data.
  */
  //存放键值对的数组
  private transient Entry[] table;

  /**

• The total number of entries in the hash table.
  */
  //大小
  private transient int count;

  /**

• The table is rehashed when its size exceeds this threshold. (The
• value of this field is (int)(capacity * loadFactor).)

• @serial
  */
  //阀值
  private int threshold;

  /**

• The load factor for the hashtable.

• @serial
  */
  //负载因子
  private float loadFactor;
  //默认初始容量为11，负载因子0.75
  public Hashtable() {
  this(11, 0.75f);
  }

  //1.8版本没有修改，没有维护红黑树结构
  public synchronized V put(K key, V value) {
  // Make sure the value is not null
  if (value == null) {
  throw new NullPointerException();
  }

  // Makes sure the key is not already in the hashtable.
  Entry tab[] = table;
  int hash = key.hashCode();
  //求余获得索引
  int index = (hash & 0x7FFFFFFF) % tab.length;
  @SuppressWarnings("unchecked")
  Entry entry = (Entry)tab[index];
  for(; entry != null ; entry = entry.next) {
      if ((entry.hash == hash) && entry.key.equals(key)) {
          V old = entry.value;
          entry.value = value;
          return old;
      }
  }
  
  addEntry(hash, key, value, index);
  return null;

  }

  /**

• Removes the key (and its corresponding value) from this
• hashtable. This method does nothing if the key is not in the hashtable.
• @param key the key that needs to be removed
• @return the value to which the key had been mapped in this hashtable,
• or null if the key did not have a mapping
• @throws NullPointerException if the key is null
  */
  public synchronized V remove(Object key) {
  Entry tab[] = table;
  int hash = key.hashCode();
  int index = (hash & 0x7FFFFFFF) % tab.length;@SuppressWarnings("unchecked")
  br/>@SuppressWarnings("unchecked")
  e = (Entry)tab[index];
  for(Entry prev = null ; e != null ; prev = e, e = e.next) {
  if ((e.hash == hash) && e.key.equals(key)) {
  modCount++;
  if (prev != null) {
  prev.next = e.next;
  } else {
  tab[index] = e.next;
  }
  count--;
  V oldValue = e.value;
  e.value = null;
  return oldValue;
  }
  }
  return null;
  }

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