Constructing objects for a user-defined generic Array in Java

Question

If I defined my own generic array with this constructor:

public PublisherGenericArray(Class<E> c, int s)
{   
    // Use Array native method to create array  
    // of a type only known at run time
    @SuppressWarnings("unchecked")
    final E[] a = (E[]) Array.newInstance(c, s);
    this.a = a;
}

How do I create an object that satisfies the first parameter (class c)?

Basically:

PublisherGenericArray <String> newArray = new <String> PublisherGenericArray(???,newSize);

What would go in the first parameter labeled "???"

Your <String> in new <String> Publis... serves no purpose here. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Aug 4, 2015 at 0:16

shmosel · Accepted Answer · 2015-08-03 23:49:44Z

2

PublisherGenericArray<String> newArray = new PublisherGenericArray<String>(String.class, newSize);

answered Aug 3, 2015 at 23:49

shmosel

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Comments

William Kinaan · Accepted Answer · 2015-08-04 16:32:45Z

1

The first parameter of your construction is a class of the parametrised type.

The parametrised type is the invocation of the generic type. For example

Foo<T> is a generic type, while in

Foo<Integer> t;

the Foo<Integer> is a parametrised type.

In your code, E is a parameter type (variable type)

there are infinity number of possible constructions. To list some:

PublisherGenericArray<Integer> t = new PublisherGenericArray<Integer>(Integer.class, 3);
    PublisherGenericArray<String> tt = new PublisherGenericArray<String>(String.class, 3);
    PublisherGenericArray<NullPointerException> ttt = new PublisherGenericArray<>(NullPointerException.class, 3);

notice in the ttt, i have used The Diamond and it just works with java SE 7 and later

You can also create your parametrised type by doing the invocation on a raw type as well

class A<T> {
        }
        PublisherGenericArray<A> tttt = new PublisherGenericArray<A>(
                A.class, 4);

edited Aug 4, 2015 at 16:32

answered Aug 4, 2015 at 16:21

William Kinaan

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1 Comment

ML. Over a year ago

Good examples! Thank you!

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