Understanding Bounded and Unbounded Wildcards in Java Generics

Explore the differences between bounded and unbounded wildcards in Java Generics, understanding their use-cases and practical applications.
---
Disclaimer/Disclosure: Some of the content was synthetically produced using various Generative AI (artificial intelligence) tools; so, there may be inaccuracies or misleading information present in the video. Please consider this before relying on the content to make any decisions or take any actions etc. If you still have any concerns, please feel free to write them in a comment. Thank you.
---
Understanding Bounded and Unbounded Wildcards in Java Generics

In the realm of Java programming, generics play a pivotal role in ensuring type safety and reducing the risk of ClassCastException. They allow developers to write flexible and reusable code. Within this context, wildcards are a powerful feature in Java generics that help in allowing polymorphic type parameters. Wildcards can be categorized into two main types: bounded and unbounded. Let's delve into the differences and uses of each.

Unbounded Wildcards

An unbounded wildcard is represented by a question mark (?). It's used when any type can be accepted as an argument. This wildcard is particularly useful when the code doesn't depend on the specific type parameter.

For example:

[[See Video to Reveal this Text or Code Snippet]]

In this example, the printList method can accept a list of any type.

Bounded Wildcards

A bounded wildcard sets a limit on the type of object that can be used. Bounded wildcards are useful when you want to work within a specific range of types. There are two types of bounded wildcards:

Upper-bounded wildcard: Denoted by ? extends Type, it restricts the unknown type to be a specific type or a subtype of that type.

Lower-bounded wildcard: Denoted by ? super Type, it restricts the unknown type to be a specific type or a supertype of that type.

Upper-Bounded Wildcards

Upper-bounded wildcards are useful in situations where you want to read but not modify the data. For example:

[[See Video to Reveal this Text or Code Snippet]]

Here, the sumOfList method can accept lists of Number or any of its subclasses (e.g., Integer, Double, etc.).

Lower-Bounded Wildcards

Lower-bounded wildcards are beneficial when you want to write to the list. For instance:

[[See Video to Reveal this Text or Code Snippet]]

In this example, the addNumbers method ensures that the list can accept Integer values or values of any supertype of Integer.

Conclusion

Understanding the differences between bounded and unbounded wildcards is essential for utilizing Java generics effectively. Unbounded wildcards offer flexibility when the type of elements is not relevant, while bounded wildcards provide a way to constrain the types to a specific range. Being adept at using these wildcards can help in creating more robust and type-safe Java applications.