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());
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}
@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)。
