Calling static method from type variable

Question

I have the class:

public class AbstractHandler {
    public static void handle(){ 
        throw new UnsupportedOperationException("Not implemented");
    }
}

which is going to have some number subclasses.

Also I have the following class which is going to use that class:

public class Consumer<T extends AbstractHandler>{

    public static void handle(){
        //I need to call the method 
        //T.handle() somehow
        //Is that possible?
    }
}

Why is #handle static anyway? Makes no sense to me, especially if you want polymorphism. — Tom
– Tom, Commented May 13, 2015 at 12:33
As stated by others - static is basically a violation of "OO concepts". One should only use it with great care; as it can make unit testing extremely hard. So besides the fact that your intended "usage" is plain wrong ... even it would somehow work: don't do it. Only make methods/objects static if there is no other way! — GhostCat
– GhostCat, Commented May 13, 2015 at 12:37
By the way, did you actually try calling T.handle();? It compiles and runs. — Radiodef
– Radiodef, Commented May 13, 2015 at 12:50

Konstantin Yovkov · Accepted Answer · 2015-05-13 12:31:56Z

5

Since the method is static, there's no need to know what exactly T is.

Just do:

AbstractHandler.handle();

answered May 13, 2015 at 12:31

Konstantin Yovkov

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Luan Nico · Accepted Answer · 2015-05-13 12:32:01Z

2

Static methods are not inherited.

So you have AbstractHandler.handle, and that does not mean every T shall have one too.

If they do, it is not the same method either - there is no connection between then, even if they have the same name.

answered May 13, 2015 at 12:32

Luan Nico

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4 Comments

Radiodef Over a year ago

"that does not mean every T shall have one too" But you can call a static method using the subclass, right? class Sub extends AbstractHandler {} Sub.handle();

Luan Nico Over a year ago

@Radiodef indeed you are correct, but only when Sub does not redefine handle; it's simply a syntax sugar as I see it, because if you do declare handle you can't add @Override annotation, can't call super.handle, et cetera, which suggests they aren't related :)

Radiodef Over a year ago

So then why can't T.handle() be the same as AbstractHandler.handle()? ; )

Luan Nico Over a year ago

I'm guessing that's because T is erased at runtime, and therefore there would be no way to know whether handle would match a child that had handle or the parent's version - unlike if, for example, you had a T t object, whose class is not erased (though T is), and then the method chain could be fetched normally. But your argument is good, it would make sense if it were possible.

Mena · Accepted Answer · 2015-05-13 12:33:05Z

1

Since the method you plan to invoke is static, simply invoke:

AbstractHandler.handle();

... in your Consumer#handle method body.

I doubt this is actually what you want to do though.

You'd probably want to change the signature of handle as instance (i.e. not static), and invoke T.handle() in your Consumer#handle method body.

answered May 13, 2015 at 12:33

Mena

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