A possible way for generic type arrays?

Does creating an array of generic objects, in this fashion, has any downsides or performance issues?

Que开发者_开发技巧ryObjects instances[] = (QueryObjects<String,String,String>[]) new Object[10];

Edit: I was even thinking if I could instead rely on this:-

QueryObjects instances[] = new QueryObjects[10];

The primary reason for this being, I do not want to fix the generic to <String,String,String> because sometimes it can also be like <Integer,Integer,Integer> for some elements of array. So I would like to give it as a runtime choice. Since this is mostly for application's internal work and not for any client side input, perhaps I should not be facing the danger of wrong inputs.

Your code will generate a ClassCastException at run time.

You should create an array of type QueryObjects[] and cast it to QueryObjects<String, String, String>[], or in the future, if you need to create an array of a variable type (e.g., T[]), use reflection: How to create a generic array in Java?

Creating it in this way does have a downside: you now have what is really an array of any kind of Object disguised as an array of QueryObjects. If someone else has a reference to the same array (and know that it is an Object[]), they could put some Object into it, e.g. a String, and then the program will throw a ClassCastException when you try to access that String through your reference to the array. Solution: create it like this:

QueryObjects<String, String, String> instances[] = new QueryObjects[10];

the "righteous" way is

QueryObjects<?,?,?>[] instances = new QueryObjects<?,?,?>[10];

the raw way is just fine:

QueryObjects[] instances = new QueryObjects[10];

notice the type declaration:

Type[] var

not

Type var[]

I don't care why Java allows the 2nd syntax, it still doesn't make any sense.

It begs the question "If you're using generics, why use an array instead of an a typed structure?"

Instead of trying to achieve QueryObjects[] and doing it poorly, why not create a type for it? Then you can add whatever methods you want. Yay object orientation!

class QuerySet<O extends QueryObjects<A,B,C>> {
    O[] objects;
}