CODEWITHSUNDEEP
javahashmap
raman r
raman r

Reputation: 41

Why Hashmap value type takes double[] but not double?

I'm developing an java application in which I use Hashmap which takes string as key and double as value, but I know Hashmap cannot take primitive type as generics but it can take double[].May I know why ?

Upvotes: 2

Views: 1685

Answers (3)

Chathura Buddhika
Chathura Buddhika

Reputation: 2195

You can't use double since it is a primitive. But you can use Double instead.

Refer following question for more detail.

Why can Java Collections not directly store Primitives types?

Upvotes: 7

Danilo M. Oliveira
Danilo M. Oliveira

Reputation: 728

You cannot use primitive types (int, boolean, double, etc.) as map keys or values. But each primitive type has one wrapper class (int - Integer, double - Double, etc.) that you can use instead.

Since Java 1.5 the conversion of primitive values to wrapper objects is automatic (it's called auto boxing/unboxing):

Map<String, Double> m = new HashMap<>();

m.add("a", 1.0 );

double a = m.get("a");

Upvotes: -1

Thilo
Thilo

Reputation: 262554

All arrays are objects in Java, including arrays of primitive types.

This means that you can use them as generic type parameters (whereas primitives cannot be used), for example as List elements or Map values. They can stand in anywhere you need an Object.

But note that arrays do not have "proper" implementations of equals or hashCode, and thus make terrible keys in a Map (values are fine).

Upvotes: 4

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