CODEWITHSUNDEEP
javaarraylistinteger
programmingIsFun
programmingIsFun

Reputation: 1075

Why can't I have 'int' as the type of an ArrayList?

I want to declare an ArrayList of type int.

Why does the following give me an error:

ArrayList<int> list1 = new ArrayList<int>();

But the following works: 

ArrayList<Integer> list1 = new ArrayList<Integer>();

?

Upvotes: 45

Views: 65245

Answers (7)

user929542
user929542

Reputation: 59

int is a primitive. It is not a Object.

Refer this link for further details.

Upvotes: 0

Soutik Samanta
Soutik Samanta

Reputation: 1

int is not an Object and hence if list type is int, implementations of the list cannot be done.

Upvotes: 0

Harish
Harish

Reputation: 3483

All the answers above answer why but the root of this question is frequent auto boxing and unboxing of the primitive data types. This problem is already solved by IntBuffer or ChadBuffer or you name the primitive type it's already there in the nio folder. Next time if you want to use primitive ArrayList don't use List instead use IntBuffer

Upvotes: 1

Suprit Behera
Suprit Behera

Reputation: 1

int is a primitive data type but Integer is a class so an arrayList array can only take reference types as its parameter not primitive type

Upvotes: 0

Zach Latta
Zach Latta

Reputation: 3341

ArrayList can only reference types, not primitives. Integer is a class, not a primitive.

When you declare ArrayList<Integer> list1 = new ArrayList<Integer>(), you're creating an ArrayList which will store the Integer type, not the int primitive.

If you want to read about the difference between primitive and reference types, check out http://pages.cs.wisc.edu/~hasti/cs302/examples/primitiveVsRef.html

Upvotes: 41

ameed
ameed

Reputation: 1170

The short answer is that generics (like ArrayList<Integer>) do not accept primitive types (int), only objects (Integer).

This is because classes like ArrayList are implemented as using Objects. Since every class inherits from Object, the compiler can just plug in other classes. But primitive types (like int) do not inherit from Object, for they are not classes. So, Sun/Oracle made the Integer class to help with this.

So, in short: int is not an Object.

Upvotes: 12

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272772

Because int is a primitive type. Only reference types can be used as generic parameters.

Upvotes: 14

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