Can't Instantiate Map…well why not?

Question

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 1

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.

Answer 2

接口无法实例化您需要使用一些实现接口的具体类尝试这样的事情

Map<String, ArrayList<Pair<String, Integer>>> k = new  HashMap<String, ArrayList<Pair<String, Integer>>>();