Map map2 = new EnumMap(map1);

Question

class Enum is defined in API as:

public abstract class Enum<E extends Enum<E>>

I have

enum Cards { Trefs(2.3), Clubs(1.0);
    public double d;

    private Cards(double val) {
        this.d = val;
    }       
}

Question 1:

Enum e = Cards.Clubs; //compiles, but with warning: "References to generic type Enum<E> should be parameterized"

Enum<???what-shall-I-write-here??> e1 = Cards.Clubs; //Question 1

Question 2:

this compiles:

        Map<Enum, Integer> map0 = new HashMap<Enum, Integer>();
        Map<Enum, Integer> map1 = new HashMap<Enum, Integer>();
        map1.put(Cards.Clubs, new Integer(54));

        Map<Enum, Integer> map2 = new EnumMap<>(map1);

But can I add anything in angle brackets of RHS (new EnumMap), like I did for map1 above?

Map<Enum, Integer> map2 = new EnumMap<???what-can-I-write-here??>(map1);

P.S. I researched SO, but found nothing DIRECTLY answering above question. My research:

Try using an IDE, it will fill almost everything. – NewUser Jan 22 '17 at 16:31 — NewUser, Jan 22 '17 at 16:31

score 1 · Accepted Answer · edited May 23 '17 at 10:29

First: please use this instead:

Cards e = Cards.Clubs;

Second: Use the diamond operator. If you absolutely want, it is new EnumMap<Cards, Integer>() but why do you want to write it out? And please never use new Integer(54). If for whatever reason you do not like autoboxing, use Integer.valueOf(54) instead. It doesn't waste objects.

So, I recommend this code:

Map<Cards, Integer> map0 = new HashMap<>();
Map<Cards, Integer> map1 = new HashMap<>();
map1.put(Cards.Clubs, 54);

Map<Cards, Integer> map2 = new EnumMap<>(map1);

Shinigami · Answer 2 · 2017-01-22T17:25:46.040

0

The first thing is:

Enum<Cards> e = Cards.Clubs;

Map<Enum<Cards>, Integer> map0 = new HashMap<>();
Map<Enum<Cards>, Integer> map1 = new HashMap<>();
map1.put(Cards.Clubs, 54);

But I don't know why the Map<Enum<Cards>, Integer> map2 = new EnumMap<>(map1); fails

Edit:

So I think what you want is something like this:

Cards e = Cards.Clubs;

Map<Cards, Integer> map0 = new HashMap<>();
Map<Cards, Integer> map1 = new HashMap<>();
map1.put(Cards.Clubs, 54);

EnumMap<Cards, Integer> map2 = new EnumMap<>(map1);

You don't need to wrap you Enum into an Enum

edited Jan 22 '17 at 17:25

answered Jan 22 '17 at 17:11

Shinigami

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Surprisingly, `Enum e = Cards.Clubs;` gives a warning "Enum is a raw type. References to generic type Enum should be parameterized". Is there a way to write this without warning? – LrnBoy Jan 22 '17 at 17:25

Map map2 = new EnumMap(map1);

2 Answers2