java - What is the point of T extends SomeClass?

Question

What is the difference with a method declaration like this:

public <T extends SomeClass> void doSomething(T obj)
{
    // Do something.
}

And this:

public void doSomething(SomeClass obj)
{
    // Do Something.
}

The way I see it, both of them are specifying that the object passed in must be a subclass of type SomeClass, so why bother with the generics at all in this instance?

Answer 1

In your case it doesn't make much difference.

But consider the following:

public <T extends SomeClass> void doSomething(List<T> obj)

In this case you could call the method the following ways:

obj.doSomething(new ArrayList<SubclassOfSomeClass>());
obj.doSomething(new ArrayList<SomeClass>());

If you would use

public void doSomething(List<SomeClass> obj)

You would only be able to do this:

obj.doSomething(new ArrayList<SomeClass>());