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

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

其他回答

这些是同一接口的不同实现。每种实现都有一些优点和缺点(快速插入，缓慢搜索)，反之亦然。

有关详细信息，请参阅TreeMap, HashMap, LinkedHashMap的javadoc。

2010-05-22 21:12:23

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:

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

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。

2015-01-30 02:28:49

虽然这里有很多很好的答案，但我想给出我自己的表，描述与Java 11绑定的各种Map实现。

我们可以在图表中看到这些差异:

HashMap is the general-purpose Map commonly used when you have no special needs. LinkedHashMap extends HashMap, adding this behavior: Maintains an order, the order in which the entries were originally added. Altering the value for key-value entry does not alter its place in the order. TreeMap too maintains an order, but uses either (a) the “natural” order, meaning the value of the compareTo method on the key objects defined on the Comparable interface, or (b) invokes a Comparator implementation you provide. TreeMap implements both the SortedMap interface, and its successor, the NavigableMap interface. NULLs: TreeMap does not allow a NULL as the key, while HashMap & LinkedHashMap do. All three allow NULL as the value. HashTable is legacy, from Java 1. Supplanted by the ConcurrentHashMap class. Quoting the Javadoc: ConcurrentHashMap obeys the same functional specification as Hashtable, and includes versions of methods corresponding to each method of Hashtable.

2019-12-17 01:36:37

HashMap, LinkedHashMap和TreeMap之间的区别

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