Java - generic array creation and the need for type casting [duplicate]

Question

Why doesn't Java allow for generic array creation? What difference does it make if it is allowed? If it is problematic then why type casting object array is not?

This is an implementation artifact of arrays - which store the type of element in the type - and generics which don't know the concrete type and are "erased". Thus all generic arrays are Object[], which requires a cast on access. Simply avoid arrays directly when dealing with generics to avoid this - or, in the implementation, apply the appropriate cast from "known context". — user2864740
– user2864740, Commented Jan 5, 2015 at 19:26
It does. You're free to do this: Object [] putAnyTypeHere = new Object[10]; — duffymo
– duffymo, Commented Jan 5, 2015 at 19:26

padawan · Accepted Answer · 2015-01-05 19:30:09Z

-1

I think what you mean by "generic array" is Object[].

Well, it creates problems because when you initialize an array with size n, you allocate n identical blocks.
For instance:

Integer[] x = new Integer[10];

Allocates 10 blocks of 4 bytes = 40 bytes.

However,

Object[] x = new Object[10];

is ambiguous because it cannot be known if you're going to store Doubles, Strings or just custom objects you've created.

answered Jan 5, 2015 at 19:30

padawan

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1 Comment

user2864740 Over a year ago

This is incorrect. Integer and Object take up the same amount of "allocation" space. Only primitive types (eg. int) behave differently from [all other] reference types. Java does not support the equivalent of C#'s value types.

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