Difference between LinkedList<?> and LinkedList<Object> [duplicate]

问题

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What is the difference between ? and Object in Java generics? (6 answers)

What does the question mark in Java generics' type parameter mean? (6 answers)

Closed 2 years ago.

Is there any difference between LinkedList< ? > and LinkedList< Object > in Java?

回答1:

This passes compilation:

LinkedList<?> list1 = new LinkedList<String> ();

This doesn't:

LinkedList<Object> list2 = new LinkedList<String> ();

i.e. a LinkedList<?> variable can be assigned any LinkedList<SomeType>. A LinkedList<Object> variable can only be assigned a LinkedList<Object> (or a raw LinkedList, which is not advised to use).

On the other hand the following add:

LinkedList<?> list1 = new LinkedList<String> ();
list1.add("x");

doesn't pass compilation, while the following does:

LinkedList<Object> list2 = new LinkedList<Object> ();
list2.add("x");

来源：https://stackoverflow.com/questions/44385926/difference-between-linkedlist-and-linkedlistobject