CODEWITHSUNDEEP
javagenerics
mikesol
mikesol

Reputation: 1197

Java generics for class and new instance

In Java, if I have:

public class Foo<T> {

  public Foo() { }

}

I can do Foo<Integer> foo = new Foo<Integer>(); but I cannot find an equivalent syntax for using the class field, meaning that something like Foo<Integer> foo = Foo<Integer>.class.newInstance(); doesn't work. Is there a way to use generics via the newInstance method?

Upvotes: 1

Views: 150

Answers (3)

newacct
newacct

Reputation: 122489

.newInstance() (and anything that uses Class) is a reflection API that fundamentally works at runtime. Therefore it has little to do with Generics which operates at compile-time.

Upvotes: 1

H&#233;ctor
H&#233;ctor

Reputation: 26084

You can do it only without parameterized type. Class.newInstance() is not quite recommendable. You can do this:

//Class<Foo<Integer>> clazz = Foo<Integer>.class; <-- Error
Class<Foo> clazz = Foo.class; // <-- Ok
Foo instance = clazz.getConstructor().newInstance();

Why is Class.newInstance() evil?

Hope it helps.

Upvotes: 1

D.R.
D.R.

Reputation: 21224

newInstance() is an API from the early days of Java - no generics back then. You have to cast the return value.

Also: there will be no future method doing that, newInstance() is used to create objects dynamically at runtime. Due to type erasure in Java there is no generic information at runtime anymore.

Upvotes: 0

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