这三个都表示从唯一键到值的映射，因此实现了Map接口。

HashMap is a map based on hashing of the keys. It supports O(1) get/put operations. Keys must have consistent implementations of hashCode() and equals() for this to work. LinkedHashMap is very similar to HashMap, but it adds awareness to the order at which items are added (or accessed), so the iteration order is the same as insertion order (or access order, depending on construction parameters). TreeMap is a tree based mapping. Its put/get operations take O(log n) time. It requires items to have some comparison mechanism, either with Comparable or Comparator. The iteration order is determined by this mechanism.

以下是HashMap和TreeMap之间的主要区别

HashMap does not maintain any order. In other words , HashMap does not provide any guarantee that the element inserted first will be printed first, where as Just like TreeSet , TreeMap elements are also sorted according to the natural ordering of its elements Internal HashMap implementation use Hashing and TreeMap internally uses Red-Black tree implementation. HashMap can store one null key and many null values.TreeMap can not contain null keys but may contain many null values. HashMap take constant time performance for the basic operations like get and put i.e O(1).According to Oracle docs , TreeMap provides guaranteed log(n) time cost for the get and put method. HashMap is much faster than TreeMap, as performance time of HashMap is constant against the log time TreeMap for most operations. HashMap uses equals() method in comparison while TreeMap uses compareTo() method for maintaining ordering. HashMap implements Map interface while TreeMap implements NavigableMap interface.

我更喜欢视觉呈现:

这是我自己使用地图的经验，关于我何时使用每种地图:

HashMap - Most useful when looking for a best-performance (fast) implementation. TreeMap (SortedMap interface) - Most useful when I'm concerned with being able to sort or iterate over the keys in a particular order that I define. LinkedHashMap - Combines advantages of guaranteed ordering from TreeMap without the increased cost of maintaining the TreeMap. (It is almost as fast as the HashMap). In particular, the LinkedHashMap also provides a great starting point for creating a Cache object by overriding the removeEldestEntry() method. This lets you create a Cache object that can expire data using some criteria that you define.

请看下图(大图)中每个类在类层次结构中的位置。TreeMap实现了SortedMap和NavigableMap，而HashMap没有。

HashTable已经过时，应该使用相应的ConcurrentHashMap类。

这三个类都实现了Map接口，并提供了基本相同的功能。最重要的区别是迭代条目的顺序:

HashMap绝对不保证迭代顺序。当添加新元素时，它甚至可以(也将会)完全改变。 TreeMap将根据键的compareTo()方法(或外部提供的Comparator)的“自然顺序”进行迭代。此外，它实现了SortedMap接口，该接口包含依赖于此排序顺序的方法。 LinkedHashMap将按照条目放入映射的顺序进行迭代

“哈希表”是基于哈希的映射的通用名称。在Java API的上下文中， Hashtable是Java 1.1时代的一个过时的类，在集合框架存在之前。它不应该再使用了，因为它的API中充满了重复功能的过时方法，而且它的方法是同步的(这会降低性能，而且通常是无用的)。使用ConcurrentHashMap而不是Hashtable。