CODEWITHSUNDEEP
javagenerics
Vaibhav
Vaibhav

Reputation: 106

Java Generics code error

I am new to Generics and trying to understand why this code compiles:

public Collection<Class<Subclass>> testFunction() {

    return Collections.singleton(Subclass.class);
}

And this code doesn't:

public Collection<Class<? extends SuperClass>> testFunction() {

    return Collections.singleton(Subclass.class);
}

My SubClass looks like this:

public class Subclass extends SuperClass{

}

Upvotes: 2

Views: 100

Answers (1)

GhostCat
GhostCat

Reputation: 140427

The above compiles fine with Java8:

class SuperClass { }
class Subclass extends SuperClass{ }

class Test {
  public Collection<Class<? extends SuperClass>> testFunction() {
    return Collections.singleton(Subclass.class);
  }
}

The point is: with Java 8, type inference was heavily reworked and improved.

So my guess here is: this doesn't compile for you because you are using Java 7; where simply spoken the compiler wasn't "good enough" to correctly resolve such kind of code.

Upvotes: 3

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