哈希映射不保留插入顺序。 的例子。Hashmap 如果您正在插入键作为

1  3
5  9
4   6
7   15
3   10

它可以存储为

4  6
5  9
3  10
1  3
7  15

链接Hashmap保留插入顺序。

的例子。 如果您正在插入键

1  3
5  9
4   6
7   15
3   10

它将存储为

1  3
5  9
4   6
7   15
3   10

和我们插入的一样。

树映射以键的递增顺序存储山谷。 的例子。 如果您正在插入键

1  3
5  9
4   6
7   15
3   10

它将存储为

1  3
3  10
4   6
5   9
7   15

@Amit: SortedMap is an interface whereas TreeMap is a class which implements the SortedMap interface. That means if follows the protocol which SortedMap asks its implementers to do. A tree unless implemented as search tree, can't give you ordered data because tree can be any kind of tree. So to make TreeMap work like Sorted order, it implements SortedMap ( e.g, Binary Search Tree - BST, balanced BST like AVL and R-B Tree , even Ternary Search Tree - mostly used for iterative searches in ordered way ).

public class TreeMap<K,V>
extends AbstractMap<K,V>
implements SortedMap<K,V>, Cloneable, Serializable

在坚果壳 HashMap:给出O(1)的数据，没有排序

TreeMap:给出O(log N)，以2为底的数据。使用有序键

LinkedHashMap:是具有链表(想想索引- skiplist)功能的哈希表，以插入树的方式存储数据。最适合实现LRU(最近最少使用)。

哈希映射不保留插入顺序。 的例子。Hashmap 如果您正在插入键作为

1  3
5  9
4   6
7   15
3   10

它可以存储为

4  6
5  9
3  10
1  3
7  15

链接Hashmap保留插入顺序。

的例子。 如果您正在插入键

1  3
5  9
4   6
7   15
3   10

它将存储为

1  3
5  9
4   6
7   15
3   10

和我们插入的一样。

树映射以键的递增顺序存储山谷。 的例子。 如果您正在插入键

1  3
5  9
4   6
7   15
3   10

它将存储为

1  3
3  10
4   6
5   9
7   15

它们都提供一个key->值映射和一种遍历键的方法。最重要的区别 这些类是时间保证和键的顺序。

HashMap offers 0(1) lookup and insertion. If you iterate through the keys, though, the ordering of the keys is essentially arbitrary. It is implemented by an array of linked lists. TreeMap offers O(log N) lookup and insertion. Keys are ordered, so if you need to iterate through the keys in sorted order, you can. This means that keys must implement the Comparable interface.TreeMap is implemented by a Red-Black Tree. LinkedHashMap offers 0(1) lookup and insertion. Keys are ordered by their insertion order. It is implemented by doubly-linked buckets.

假设你将一个空的TreeMap, HashMap和LinkedHashMap传递给下面的函数:

void insertAndPrint(AbstractMap<Integer, String> map) {
  int[] array= {1, -1, 0};
  for (int x : array) {
    map.put(x, Integer.toString(x));
  }
  for (int k: map.keySet()) {
   System.out.print(k + ", ");
  }
}

它们的输出如下所示。

对于HashMap，在我自己的测试中，输出是{0,1，-1}，但它可以是任何顺序。没有任何保证 排序。 Treemap，输出为{- 1,0,1} LinkedList，输出为{1，-1,0}

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.

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.