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javapolymorphismparameterized

Java: parameterizing Map object

I have the following global variable:

private Map<String,List<String>> network;

I instantiate it in my constructor like this:

network = new Hashtable<String,ArrayList<String>>();

The above instantiation does not compile. Apparently when I parametrize the Map, I must declare that it is a mapping specifically from String to ArrayList instead of using the more general List? Any insight as to why I must do this?

Solution

  • Sorry, you can't subclass the internal class:

    network = new Hashtable<String,List<String>>();

    But when you add a member, you can create the value as an arraylist.

    network.put("Key", new ArrayList<String>());