What is a bounded type parameter?

Expert Posts
,
1

Bounded Type Parameter

  • A bounded type parameter in Java is a generic type parameter that is restricted (or bounded) to a specific type or a set of types.
  • This type parameter can only accept values of the specified type or its subclasses (in case of upper bounds) or its superclasses (in case of lower bounds).
  • This allows you to enforce type safety while still maintaining flexibility with generics.

Types of Bounded Type Parameters:

1. Upper Bounded Type Parameter (extends):

  • Restricts the type to a specific class or its subclasses.
  • Example:

java public class Box<T extends Number> { private T value; } * Here, T can only be a subclass of Number (e.g., Integer, Double).

2. Lower Bounded Type Parameter (super):

  • Restricts the type to a specific class or its superclasses.
  • Example:

java public static <T> void addNumber(List<? super Integer> list) { list.add(10); }

Why Use Bounded Type Parameters?

1. Type Safety:

  • Ensures only specific types are allowed, preventing incorrect usage.
  • Example: T extends Number ensures only number types like Integer or Double can be used.

2. Access to Methods:

  • Allows the use of methods specific to the bounded type.
  • Example: T extends Number lets you call doubleValue() on any T.

3. Flexibility with Restrictions:

  • Enables generic classes or methods to work with a range of types while maintaining constraints.