Hashtable 的实现原理概述和 HashMap 一样，Hashtable 也是一个散列表，它存储的内容是键值对。
Hashtable 在 Java 中的定义为：
public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, java.io.Serializable{}
从源码中，我们可以看出，Hashtable 继承于 Dictionary 类，实现了 Map, Cloneable, java.io.Serializable接口。其中Dictionary类是任何可将键映射到相应值的类（如 Hashtable）的抽象父类，每个键和值都是对象（源码注释为：The Dictionary class is the abstract parent of any class, such as Hashtable, which maps keys to values. Every key and every value is an object.）。但在这一点我开始有点怀疑，因为我查看了HashMap以及TreeMap的源码，都没有继承于这个类。不过当我看到注释中的解释也就明白了，其 Dictionary 源码注释是这样的：NOTE: This class is obsolete. New implementations should implement the Map interface, rather than extending this class. 该话指出 Dictionary 这个类过时了，新的实现类应该实现Map接口。
Hashtable 源码解读成员变量Hashtable是通过"拉链法"实现的哈希表。它包括几个重要的成员变量：table, count, threshold, loadFactor, modCount。
关于变量的解释在源码注释中都有，最好还是应该看英文注释。
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/** * The hash table data. */ private transient Entry<K,V>[] table; /** * The total number of entries in the hash table. */ private transient int count; /** * The table is rehashed when its size exceeds this threshold. (The * value of this field is (int)(capacity * loadFactor).) * * @serial */ private int threshold; /** * The load factor for the hashtable. * * @serial */ private float loadFactor; /** * The number of times this Hashtable has been structurally modified * Structural modifications are those that change the number of entries in * the Hashtable or otherwise modify its internal structure (e.g., * rehash). This field is used to make iterators on Collection-views of * the Hashtable fail-fast. (See ConcurrentModificationException). */ private transient int modCount = 0;[url=][/url]
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