Java Generics: What\'s the Difference Between `List`, `List`, and `List`?

Java Generics: List, List

Introduction

Java Generics provide a mechanism for creating type-safe collections that can hold objects of specific types. In this article, we'll explore the differences between three variations of the List interface: List, List

Understanding the Differences

1. List (Raw Type)

List is the raw type of the List interface. It does not specify any type arguments, which means it can hold objects of any type. However, raw types are generally discouraged as they introduce potential type safety issues.

2. List

List

3. List> (Wildcard Type)

List> is a wildcard type that denotes a list of unknown type. It can hold objects of any type, but it cannot be used to add new objects to the list. The wildcard type is primarily used as a parameter type to indicate that a method can accept lists of any type.

When to Use Each Type

1. List (Raw Type)

• Use List when the type of objects stored in the list is irrelevant or not known at compile time.
• However, be aware of potential type safety issues and consider using parameterized types whenever possible.

2. List

• Use List
• Note that this type is less flexible than the wildcard type.

3. List> (Wildcard Type)

• Use List> when you need a method parameter that can accept lists of any type.
• This type provides greater flexibility but prohibits adding new objects to the list.

Example Method Signatures

1. CanYouGiveMeAnAnswer(List l)

This method can accept any type of list, including raw lists and parameterized lists, because List is the superclass of all list types.

2. CanYouGiveMeAnAnswer(List

This method can only accept parameterized lists of type Object. It cannot accept raw lists or lists of any other type.

3. CanYouGiveMeAnAnswer(List> l)

This method can accept any type of list, including raw lists and parameterized lists, but it cannot add new objects to the list.

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