The method put> is not applicable for the argument >

Question

public class Declaration {}

public class Class_object extends Declaration{}

above is my class declaration, so basically Class_object is subclass of class Declaration.

    Map<String,ArrayList<Declaration>> structure = new HashMap<String,ArrayList<Declaration>>();
    ArrayList<Class_object> co = new ArrayList<Class_object>();
    structure.put("CLASS", co);//here gives error:The method put(String, ArrayList<Declaration>) in the type Map<String,ArrayList<Declaration>> is not applicable for the arguments (String, ArrayList<Class_object>)

In another class, I try to create a hashmap to contain different subclasses of Declaration, but it gives me error message. Could anyone tell me how to fix it?

Do you know why `ArrayList d = new ArrayList();` isn't allowed? — user253751, Feb 13 '15 at 23:21

Reimeus · Answer 1 · 2015-02-13T23:27:52.583

1

Generics are invariant. You could do

Map<String, List<? extends Declaration>> structure 
            = new HashMap<String, List<? extends Declaration>>();

edited Feb 13 '15 at 23:27

answered Feb 13 '15 at 23:08

Reimeus

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score 0 · Answer 2 · answered Feb 13 '15 at 23:09

You will have to use the extends keyword to be able to put subclasses of Declaration in your map. Define it like so:

Map<String,ArrayList<? extends Declaration>> structure = new HashMap<String,ArrayList<? extends Declaration>>();

? extends Declaration lets java know that you want to be able to use use any classes that extend Declaration, such as Class_object.

The method put> is not applicable for the argument >

2 Answers2