How to keep the order of elements in hashtable

java hashtable linkedhashmap
Thomas Manalil picture Thomas Manalil · Sep 14, 2009 · Viewed 28.8k times · Source

I have a hashtable . values() method returns values in some order different from the order in which i am inserted.How can i get the values in the same order as i inserted?Using LinkedHashmap is an alternative but it is not synchronized.

Answer

cletus picture cletus · Sep 14, 2009

Use a 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.)

combined with Collections.synchronizedMap().

So, for example:

Map<String, String> map = Collections.synchronizedMap(
  new LinkedHashMap<String, String>());

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