/**

      * 使用指定的初始容量和装载因子构造一个空的Hashtable.

      *

      * @param      initialCapacity   hashtable的初始容量

      * @param      loadFactor        hashtable的装载因子

      * @exception  IllegalArgumentException  如果初始容量小于0，或装载因子是负数，则抛出IllegalArgumentException异常

      */

     public Hashtable(int initialCapacity, float loadFactor) {

         if (initialCapacity < 0)

             throw new IllegalArgumentException("Illegal Capacity: "+

                                                initialCapacity);

         if (loadFactor <= 0 || Float.isNaN(loadFactor))

             throw new IllegalArgumentException("Illegal Load: "+loadFactor);

         if (initialCapacity==0)

             initialCapacity = 1;

         this.loadFactor = loadFactor;

         table = new Entry<?,?>[initialCapacity];

         threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);

     }

     /**

      * Constructs a new, empty hashtable with the specified initial capacity

      * and default load factor (0.75).

      *

      * @param     initialCapacity   the initial capacity of the hashtable.

      * @exception IllegalArgumentException if the initial capacity is less

      *              than zero.

      */

     public Hashtable(int initialCapacity) {

         this(initialCapacity, 0.75f);

     }

     /**

      * Constructs a new, empty hashtable with a default initial capacity (11)

      * and load factor (0.75).

      */

     public Hashtable() {

         this(11, 0.75f);

     }

     /**

      * Constructs a new hashtable with the same mappings as the given

      * Map.  The hashtable is created with an initial capacity sufficient to

      * hold the mappings in the given Map and a default load factor (0.75).

      *

      * @param t the map whose mappings are to be placed in this map.

      * @throws NullPointerException if the specified map is null.

      * @since   1.2

      */

     public Hashtable(Map<? extends K, ? extends V> t) {

         this(Math.max(2*t.size(), 11), 0.75f);

         putAll(t);

     }