What are bounded type parameters in Java?

Table of Contents

• Introduction
• Bounded Type Parameters in Java
  • Upper Bounded Type Parameters
  • Example: Using Upper Bounded Type Parameters
  • Multiple Bounded Type Parameters
  • Example: Multiple Bounds
• Benefits of Bounded Type Parameters
• Conclusion

Introduction

In Java, bounded type parameters are used to place restrictions on the types that can be accepted by generic classes or methods. By setting these bounds, you can limit a generic type to a specific hierarchy of classes, ensuring type safety and flexibility while allowing the class or method to operate on a restricted set of types. This feature is particularly useful when you want to work with generic types but also want to enforce that the type conforms to a certain class or interface.

Bounded Type Parameters in Java

Upper Bounded Type Parameters

An upper bound on a type parameter restricts the generic type to be a specific class or any subclass of that class. In Java, the **extends** keyword is used to set an upper bound for a generic type parameter.

Syntax:

Here, T can be any class that is a subclass of SuperClass or the SuperClass itself.

Example: Using Upper Bounded Type Parameters

Let's create a generic method that works only with types that extend Number, ensuring that only numeric types can be passed.

In this example, the method add uses T extends Number, meaning T can be any type that extends Number, such as Integer, Double, or Float. This ensures type safety by allowing only numeric types while still being flexible enough to work with different number subclasses.

Multiple Bounded Type Parameters

You can also define multiple bounds for a generic type by using the & operator. This allows you to enforce that a type must extend multiple classes or implement multiple interfaces.

Syntax:

Example: Multiple Bounds

In this case, T must be a subclass of Number and also implement MyInterface. This adds further constraints and ensures that any type passed to this class meets both criteria.

Benefits of Bounded Type Parameters

1. Type Safety: Bounded type parameters ensure that generic code only operates on allowed types, reducing runtime errors.
2. Code Reusability: By defining bounds, you can reuse the same generic code for different but related types.
3. Flexibility: Bounded type parameters provide flexibility by allowing different types to be passed, as long as they meet the specified bounds.

Conclusion

Bounded type parameters in Java provide a powerful way to enforce constraints on generic types, ensuring that your code remains both type-safe and flexible. By using the extends keyword for upper bounds or combining multiple bounds, you can create generic classes and methods that are adaptable yet restricted to specific hierarchies of types. This enhances the reusability and robustness of your code, making it easier to maintain and extend.