CODEWITHSUNDEEP
java
user2057312
user2057312

Reputation: 33

Generic Type extending an Final Class

In java Final classes can't be extended by normal classes but a generic type can be extended. What does this signify? For example Integer is a final class in JAVA API this class cant be extended but the following code does not show any error. 

public class SampleClass<T extends Integer> {

// memebers

}

Upvotes: 0

Views: 731

Answers (2)

Aniket Inge
Aniket Inge

Reputation: 25725

That is because the compiler expects T to be of type Integer or a type that derives from Integer.

Since Integer is final class, T can only be Integer.

The error can only happen when you're trying to create a type from Integer

for example, the compiler will throw an error here:

class IncompilableInteger extends Integer { }

because it is trying to create a type from Integer, but this won't:

class Compilable <T extends Integer> { }

because it is trying to create a type that contains object(s) of type - either is an Integer or a type that derives from Integer but not a different Integer by itself.

Upvotes: 1

Ted Hopp
Ted Hopp

Reputation: 234847

Although the code shows no errors, any actual binding of the type parameter T will have to be to an Integer since, as you correctly note, Integer is a final class. The generic type parameter, while it uses the extends keyword, is not defining an actual class; hence there is no error in the code you posted.

Upvotes: 4

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