How do I store multiple values on a map?

How do I store multiple values on a map?

21 Answers

1. Use a map that has a list as the value. Map> .
2. Create a new wrapper class and place instances of this wrapper in the map. Map .
3. Use a tuple like class (saves creating lots of wrappers). Map> .
4. Use mulitple maps side-by-side.

Can a Key have multiple values in Java?

It seems like an oversight for the standard Java API not to have a collection class that allows a key to have multiple values. Stick with the standard APIs and add a collection class like a ‘Vector’ or ‘ArrayList’ to your map or set. Use the MultiMap and MultiValueMap classes from the Apache Commons library.

Can we insert duplicate key in HashMap?

HashMap doesn’t allow duplicate keys but allows duplicate values. HashMap allows null key also but only once and multiple null values.

Can a C++ map have duplicate keys?

STL map does not allow same Keys to be used. You may want to go for multi-map for that. a map will not throw any compile/run time error while inserting value using duplicate key. but while inserting, using the duplicate key it will not insert a new value, it will return the same exiting value only.

How do you access values in a multimap?

To retrieve the value of a multimap you need to use its name. Once you have its value, you can copy it into another multimap, or you can call member functions on it to decompose its value into smaller logical subvalues.

How to map multiple values under the same key?

If you call put (K, V) twice, with the same key but different values, the multimap contains mappings from the key to both values. I use Map for associating multiple values with a key in a Map.

Can a map have more than one value?

As others pointed, Map by specification can have only one value for a given key. You have 2 solutions: As described in Map interface documentation Map contains a set of keys, so it is not capable of containing multiple non-unique keys. I suggest you to use lists as values for this map.

How to associate multiple values with the same key?

A collection similar to a Map, but which may associate multiple values with a single key. If you call put (K, V) twice, with the same key but different values, the multimap contains mappings from the key to both values. I use Map for associating multiple values with a key in a Map.

How to add multiple map entries without overwriting?

You can use putAt and getAt for syntatic sugar in map operations. You can also try a mixin in a map object.