What is the difference between of using Collection<?> and Collection<Object>

[santhosh.R gowda]

Dear All,

I want to know the difference between Collection<?> and Collection<Object>

 

public void print(Collection<Object>0)
{

}


public void print(Collection<?>0)
{

}

they are telling

Object is not a super type of all kinds of collections

Please can you elaborate this statement because Object is super of all the kinds as i know

[Christophe Verré]

You can use the Edit button () to edit your post. I have copy/pasted your second message into the first one this time.

[Rob Spoor]

Collection<Object> is just that - a Collection with generic type Object. You can retrieve elements as Object references and put any object in it.
Collection<?> is a Collection with an unknown generic type. It could be Integer, String or anything else. Since the type is unknown elements can only be retrieved as references to the common super type -- Object. However, since you don't know the type you can't add anything but null. Anything else might lead to problems later on (e.g. if the actual generic type is Integer and you add a String -- oops!).

So that's the difference: with <?> you can't add anything, with <Object> you can.