Does "put" overwrite existing values?

java hashmap hashtable
Ben picture Ben · Aug 27, 2011 · Viewed 88.8k times · Source

New to hashtables with a simple question. For some reason googling hasn't gotten me a straight answer. Say I've got an <int,String> hashtable set up:

myHashtable.put(1,"bird");
myHashtable.put(2,"iguana");

and I want to change "bird" to "fish" (and leave the index the same). Can I just do a simple put, or do I need to delete the entry, or what?

Answer

Paul Bellora picture Paul Bellora · Aug 27, 2011

Yes.

If a mapping to the specified key already exists, the old value will be replaced (and returned). See Hashtable.put().

For multi-threaded environment, I'd recommend ConcurrentHashMap or another ConcurrentMap implementation. Though Hashtable is synchronized, there are more sophisticated implementations available now for concurrent mapping, such as Guava's MapMaker and CacheBuilder.

Also keep in mind the Map is going to have the type parameters <Integer, String> since primitive type parameters aren't supported.

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