CODEWITHSUNDEEP
javagenericsmethodsinterface
MDP
MDP

Reputation: 4267

Generic method inside interface

Let's say I have this interface:

public interface i{ 
     void setImage(Image image);
}

I want that class methods that implements that interface method are allowed to accept as method paramether not only Image, but all classes that extends Image.

What I need inside the interface is something like:

<T extends Image> void setImage(T image);

But of course, this is not the right way to do it How should I write a generic method in an Interface?

Upvotes: 2

Views: 3084

Answers (2)

Andy Turner
Andy Turner

Reputation: 140319

You are allowed to declare the method with the generic in the interface:

<T extends Image> void setImage(T image);

but this actually isn't very much use: the only methods you can invoke on image are those defined on Image, so you might as well just declare it non-generically:

void setImage(Image image);

and this will accept parameters of type Image or any subclass.

Declaring a method-level type variable might be useful if, say, you wanted to return a variable of the same type as the parameter:

<T extends Image> T setImage(T image);

or if you need to constrain generic parameters to types related to other parameters:

<T extends Image> void setImage(T image, List<T> imageList);

It wouldn't help you without generic parameters, e.g.

<T extends Image> void setImage(T image1, T image2)

since you could pass in any two subclasses of Image; again, you may as well do it non-generically.

Upvotes: 8

Rambler
Rambler

Reputation: 5482

You can try like this : 

public interface i<M extends Image>{ 
     void setImage(M image);
}

Upvotes: 0

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