Why do I get an error if I try to put values into a map in my view class?

Question

I am trying to append values to a map in a scala class.

I have a generic map with question / answerList pairs in my controller class:

static Map<Question, List<Answer>> myMap = new HashMap<Question, List<Answer>>();

Question question1 = new Question("xyz", "Do Androids dream?", 127, "Marcus");
Answer answer11 = new Answer("zab", "xyz", "Only of electric sheep!", 70, "Sarah");

List<Answer> answerList1 = new ArrayList<Answer>();
answerList1.add(answer11);

// puts the question and its answers into the hashmap
myMap.put(question1, answerList1);

public static Result askQuestion(){
return ok(views.html.questionAnswer.render(myMap)); 
}

In my viewclass I add a new question / answer pair into the map:

@import model.Question
@import model.Answer

@(myMap: Map[Question, List[Answer]])

@main("Ask question"){
@myMap.put(new Question("id123", "questiontext", 34, "userID"), new List[Answer]);
}

But when I run the code the error page comes up, saying: "trait List is abstract; cannot be instantiated". Why cant I put a (question, List[answer]) pair into my map?

Answer 1

You get an error because, just as your error message states: you can not instantiate an abstract class.

You'll need to instantiate a subclass of it.

new List[Answer]

will never work. Instantiate a subclass that suits your needs.

Answer 2

As Stultuske and Kulu Limpa have pointed out you need to instantiate a subclass. This will work:

// Note: You need to tell the compiler which type Nill should use
@myMap.put(new Question("id123", "questiontext", 34, "userID"), Nil: List[Answer]);