Can't Instantiate Map...well why not?

java instantiation
PinkElephantsOnParade picture PinkElephantsOnParade · Oct 25, 2013 · Viewed 56.2k times · Source 
Map<String, ArrayList<Pair<String, Integer>>> k = new  Map<String, ArrayList<Pair<String, Integer>>>();

This line is in my code. I'd like to instantiate a Map that contains a String then an ArrayList of Pairs of Strings and Integers.

Pair is a class that I wrote that is in my package.

I get "Cannot Instantiate the type Map>>();

Why not? Seems reasonable to me...

Answer

rgettman picture rgettman · Oct 25, 2013

The built-in Map is an interface, which cannot be instantiated. You can choose between lots of implementing concrete classes on the right side of your assignment, such as:

  • ConcurrentHashMap
  • HashMap
  • LinkedHashMap
  • TreeMap

and many others. The Javadocs for Map lists many direct concrete implementations.

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