HashMap, LinkedHashMap和TreeMap之间的区别

HashMap, LinkedHashMap和TreeMap在Java中的区别是什么? 我在输出中没有看到任何不同，因为这三个都有keySet和values。什么是哈希表?

Map m1 = new HashMap();
m1.put("map", "HashMap");
m1.put("schildt", "java2");
m1.put("mathew", "Hyden");
m1.put("schildt", "java2s");
print(m1.keySet()); 
print(m1.values()); 

SortedMap sm = new TreeMap();
sm.put("map", "TreeMap");
sm.put("schildt", "java2");
sm.put("mathew", "Hyden");
sm.put("schildt", "java2s");
print(sm.keySet()); 
print(sm.values());

LinkedHashMap lm = new LinkedHashMap();
lm.put("map", "LinkedHashMap");
lm.put("schildt", "java2");
lm.put("mathew", "Hyden");
lm.put("schildt", "java2s");
print(lm.keySet()); 
print(lm.values());

当前回答

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.

2012-08-27 18:51:24

其他回答

我更喜欢视觉呈现:

Property	HashMap	TreeMap	LinkedHashMap
Iteration Order	no guaranteed order, will remain constant over time	sorted according to the natural ordering	insertion-order
Get / put / remove / containsKey	O(1)	O(log(n))	O(1)
Interfaces	Map	NavigableMap, Map, SortedMap	Map
Null values/keys	allowed	only values	allowed
Fail-fast behavior	Fail-fast behavior of an iterator cannot be guaranteed, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification	Fail-fast behavior of an iterator cannot be guaranteed, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification	Fail-fast behavior of an iterator cannot be guaranteed, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification
Implementation	buckets	Red-Black Tree	double-linked buckets
Is synchronized	implementation is not synchronized	implementation is not synchronized	implementation is not synchronized

2013-07-17 19:24:52

这是我自己使用地图的经验，关于我何时使用每种地图:

2012-08-27 18:51:24

HashMap: 不维持秩序比LinkedHashMap快用于存储对象堆 LinkedHashMap: LinkedHashMap插入顺序将被维持比HashMap慢，比TreeMap快如果你想保持一个插入顺序，使用这个。 TreeMap: TreeMap是一种基于树的映射 TreeMap将遵循键的自然顺序比HashMap和LinkedHashMap慢在需要维护自然(默认)排序时使用TreeMap

2018-05-27 11:15:00

HashMap绝对不保证迭代顺序。它当添加新元素时，甚至会完全改变。 TreeMap将根据键的“自然顺序”进行迭代根据它们的compareTo()方法(或外部提供的比较器)。此外，它实现了SortedMap接口，其中包含依赖于此排序顺序的方法。LinkedHashMap 将按照条目放入映射中的顺序进行迭代

看看性能是如何变化的。

树映射是排序映射的实现。由于自然排序，put、get和containsKey操作的复杂度为O(log n)

2013-07-17 17:29:48

HashMap

它有一对值(键，值) 禁止复制键值无序的无序它允许一个空键和多个空值

哈希表

和哈希映射一样它不允许空键和空值

LinkedHashMap

它是map实现的有序版本基于链表和哈希数据结构

TreeMap

有序和排序版本基于哈希数据结构

2011-10-18 04:55:52