数据结构在Java中，我如何访问在树状图中放置元素的顺序？

Question

假设我把键“a”、“b”、“c”放进aTreeMap。我如何使用“c”来确定它是TreeMap中的第三个词汇顺序元素

从树形图中获取NavigableSet的目的是什么

Answer 1

如果要按插入顺序检索元素，请使用LinkedHashMap

LinkedHashMap

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order). Note that insertion order is not affected if a key is re-inserted into the map. (A key k is reinserted into a map m if m.put(k, v) is invoked when m.containsKey(k) would return true immediately prior to the invocation.)

Answer 2

如果您真正想知道的是映射中包含的已排序键集中c键的索引，那么您可以使用

int index = map.headMap("c").size(); 

请注意，它与插入顺序没有任何关系，树映射不会维护插入顺序