Mastering Java: The Ultimate Quiz for 'Thinking in Java'

Why might you use List<? extends Object> instead of List<?>?

1. To clarify that objects in the List extend Object

2. To allow addition of any object type to the List

3. There is no practical use; they mean the same thing

4. To differentiate from raw types in method signatures

The correct answer is: There is no practical use; they mean the same thing

List<?> and List<? extends Object> essentially have the same meaning, as both are wildcard types that can store any type of objects. Therefore, there is no practical difference in using one over the other. Option A is incorrect because the keyword "extends" is not necessary when using the wildcard "?". Option B is incorrect as both options allow for the addition of any object type to the list. Option D is incorrect because the usage of wildcard types is not related to differentiating from raw types in method signatures.