Bounded Type Parameters in Java
Table of Contents
- Introduction
- Understanding Bounded Type Parameters in Java
- Practical Example
- Key Takeaways
- Conclusion
1. Introduction
In Java, generics enable types (classes and interfaces) to be parameters when defining classes, interfaces, and methods. A specific feature within generics is bounded type parameters. This article explains bounded type parameters, their importance, and how they can improve the reusability and type safety of your Java code.
Bounded type parameters allow you to restrict the types that can be used as arguments for a generic type. For instance, you can declare that a type parameter must be a subclass of a particular class or implement a specific interface.
2. Understanding Bounded Type Parameters in Java
When working with generics, there may be cases where you want to restrict the types that can be used as arguments. This is where bounded type parameters come in. A bounded type parameter is one that is restricted to a specific range of types.
For example:
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class Data<K extends Integer, V> { // Class implementation } |
Here, the type parameter K is bound to the type Integer, which means you can only use Integer (or its subclasses, if any) as the type argument for K.
Types of Bounded Type Parameters:
- Upper Bounded: Restricts the type parameter to be a specific type or any subclass of that type.
Syntax:
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<T extends ClassName> |
- Lower Bounded: Allows you to specify that the type parameter can be any type that is a superclass of a given type.
Syntax:
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<T super ClassName> |
Bounded types ensure type safety in Java and are particularly useful when you want to enforce a specific hierarchy or behavior.
3. Practical Example
Let’s analyze a simple Java program that demonstrates the use of bounded type parameters:
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package org.studyeasy; import java.util.List; class Data<K extends Integer, V> { private K key; private V value; public Data(K key, V value) { this.key = key; this.value = value; } public K getKey() { return key; } public V getValue() { return value; } public <N extends Number, E> void display(N number, E element) { System.out.println("Number: " + number + " Element: " + element); } } public class Main { public static void main(String[] args) { Data<Integer, String> data = new Data<>(1, "Chaand"); data.display(25.5254f, '£'); } } |
3.1 Code Walkthrough
- Class Declaration: The class
Datauses bounded type parameters. The type parameterKis restricted toIntegeror its subclasses. The second type parameter,V, is unbounded, meaning it can accept any object type. - Constructor: The constructor of the
Dataclass initializes the key-value pair. - Method with Bounded Type: The
displaymethod uses two more type parameters:N, which extendsNumber, andE, which can be any type. This method demonstrates how bounded types can be used with method arguments.
Output:
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Number: 25.5254 Element: £ |
When you run the program, it will output the above result, demonstrating the flexibility of bounded type parameters in Java.
4. Key Takeaways
Bounded type parameters in Java allow you to restrict generic type parameters to specific types or interfaces. They improve type safety and help enforce relationships between generic types.
| Bounded Type Parameter | Description | Example |
|---|---|---|
Upper Bounded (extends) |
Restricts to a specific class and its subclasses | <T extends Number> |
Lower Bounded (super) |
Allows a type and its superclasses | <T super Number> |
5. Conclusion
Bounded type parameters in Java provide flexibility and control over generic types, ensuring that your code is safe, extensible, and type-specific. They allow you to work with a limited range of types, making your programs more predictable and less prone to runtime errors.