CODEWITHSUNDEEP
javagenerics
user1079065
user1079065

Reputation: 2205

Generics in Java -- implementing interfaces

I have an interface with prototype

public interface genericInterface <E extends Comparable <E>>{}

and now I want to implement this inerface in my class, what I should wirte in class definition? The following line is giving me an error (I have implemented all the methods in the interface)

public class MyClass<Integer> implements genericInterface**<Integer Comparable<Integer>>**{ }

Syntax...

genericInterface<Integer Comparable<Integer>> -- error

genericInterface<Integer> -- error

what I should write in place of <Integer Comparable<Integer>> to make it compatible?

Upvotes: 1

Views: 116

Answers (2)

Russell Zahniser
Russell Zahniser

Reputation: 16354

The class declaration should just be:

class MyClass implements genericInterface<Integer>

Generic parameters after the class name are for parameters of that class, not of classes that it is implementing.

So, for example:

interface genericInterface<E extends Comparable <E>> {
    E getKey();
}
class MyClass<T> implements genericInterface<Integer> {
    T getValue();
}

MyClass<String> m = new MyClass<String>();
Integer a = m.getKey(); // Because MyClass always has E = Integer
String b = m.getValue(); // Because m has T = String

genericInterface<Integer> g = new MyClass<Boolean>();
Integer c = g.getKey();

You can also do:

class MyClass<E extends Comparable <E>> implements genericInterface<E>

Then you can have instances of MyClass parameterized with any type that would work for genericInterface.

Upvotes: 9

mkrakhin
mkrakhin

Reputation: 3486

Generics are available in Java only since version 1.5. You should use raw types.

Upvotes: 0

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