Generics in Java -- implementing interfaces

Question

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?

You can't use generics pre java 1.5.

Ben Thurley
– Ben Thurley

2014-02-11 15:05:31 +00:00
Commented Feb 11, 2014 at 15:05 — Ben Thurley
– Ben Thurley, Commented Feb 11, 2014 at 15:05
I am using java 1.7...

user1079065
– user1079065

2014-02-11 15:06:13 +00:00
Commented Feb 11, 2014 at 15:06 — user1079065
– user1079065, Commented Feb 11, 2014 at 15:06
You should change your Java 1.4 tag then.

Tyler
– Tyler

2014-02-11 15:07:34 +00:00
Commented Feb 11, 2014 at 15:07 — Tyler
– Tyler, Commented Feb 11, 2014 at 15:07

Russell Zahniser · Accepted Answer · 2014-02-11 15:13:25Z

9

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.

edited Feb 11, 2014 at 15:13

answered Feb 11, 2014 at 15:07

Russell Zahniser

16.4k41 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user1079065 Over a year ago

Hi, thanks a lot but then if I have a method in the interface method(Myclass<E> arg1) would give me an error right? saying that myclass is not generic , it should be parametrized with <E>

mkrakhin · Accepted Answer · 2014-02-11 15:05:17Z

0

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

answered Feb 11, 2014 at 15:05

mkrakhin

3,4861 gold badge24 silver badges34 bronze badges

2 Comments

Kumar Abhinav Over a year ago

He said he is using java 1.7.So there should be no reason why he should not be using powerful features of geenrics

mkrakhin Over a year ago

I left answer before he left comment about 1.7. Also, previously question had tag java 1.4

Collectives™ on Stack Overflow

Generics in Java -- implementing interfaces

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related