Java Generics: What's the Difference Between `List

Java Generics: Understanding Wildcards

Wildcards in Java generics provide a powerful tool for defining flexible data structures that can operate on various types. Here are the answers to your questions:

1. Difference between List extends T> and List super T>

List extends T> represents a wildcard with an upper bound. It specifies that the type can be T or any subtype of T. This type allows you to add elements of type T or its subtypes to the list, but it does not allow you to retrieve elements of that specific type.

List super T>, on the other hand, represents a wildcard with a lower bound. It specifies that the type can be T or any supertype of T. This type allows you to retrieve elements of type T or its superclass, but it does not allow you to add elements of that specific type.

2. Bounded vs Unbounded Wildcards

• Bounded Wildcards: As explained above, bounded wildcards specify a constraint on the type using upper bounds (extends) or lower bounds (super).
• Unbounded Wildcards: Unbounded wildcards are represented by simply >. They eliminate all type safety checks and allow any type of object to be stored or retrieved from the collection. However, they offer less type safety compared to bounded wildcards.

Additional Resources:

• [Java Tutorials - Wildcards](https://docs.oracle.com/javase/tutorial/extra/generics/wildcards.html)
• [Java Tutorials - More Fun with Wildcards](https://docs.oracle.com/javase/tutorial/extra/generics/wildcardsMoreFun.html)

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