A Guide to Java Abstraction

Abstraction is a fundamental concept in object oriented programming (OOP) that allows developers to represent complex systems by simplifying them into their essential characteristics, while hiding unnecessary implementation details. This programming tutorial will discuss abstraction, its benefits and how it can be implemented in Java.

What is Abstraction in Java?

Abstraction refers to the practice of hiding implementation details and providing a simplified view of a system to its users. It is used to simplify complex systems by exposing only the necessary features and behaviors, while hiding the underlying complexity.

Abstraction is important because it helps to simplify code, making it easier to use, maintain, and extend. By providing a simplified view of a system, abstraction helps to encapsulate complexity, making it easier to manage and work with.

Abstraction also promotes code reuse, as abstract classes and interfaces can be used as templates for creating new classes with similar behavior. In Java, abstraction is implemented through two primary mechanisms: abstract classes and interfaces.

Before going further, if you need to refresh your memory on OOP concepts – or are new to object oriented programming – we recommend checking out the following tutorials:

What is an Abstract Class in Java?

A class in Java can be either concrete or abstract. Unlike a concrete class, an abstract class provides a common interface for its subclasses to implement and cannot be instantiated.

The following code example illustrates how to implement an abstract class in Java:

abstract class Vehicle {
    abstract void move();
}
public class Car extends Vehicle {
    void move() {
        System.out.println("Inside the move method of the Car class...");
    }
    public static void main(String args[]) {
        Vehicle obj = new Car();
        obj.move();
    }
}

Here are some important points to remember regarding abstract classes in Java:

• An abstract class in Java is declared using the abstract keyword
• An abstract class in Java can have constructors, final methods, and also static members
• You can extend an abstract class in Java but you can’t instantiate it
• An abstract class in Java comprises abstract as well as non-abstract members

You can learn more about constructors in our tutorial: Working with Constructors in Java.

What is an Abstract Method in Java?

Abstract methods are those that do not have any implementation in the abstract class and are declared using the abstract keyword, and they must be implemented by the subclasses that extend the abstract class.

The preceding code example illustrates an abstract method named move. Note how the method is implemented in the Car class. Here is another code example that shows an abstract method accelerate () in a class named Vehicle:

public abstract class Vehicle {
   protected int yearOfManufacture;
   
   public Vehicle(int yearOfManufacture) {
      this.yearOfManufacture = yearOfManufacture;
   }
      public abstract void accelerate();
}

What is an Interface in Java?

An interface is a type that is used to define a contract for a set of behaviors that a class can implement. It provides a way to achieve abstraction and is used to define the API (Application Programming Interface) for a module or component.

In order to declare an interface, programmers use the interface keyword, and by default, the methods inside the interface are public and abstract. In order to implement an interface, a class must implement all methods declared in the interface.

Here is an example of an interface in Java:

public interface Shape {
   public double getArea();
   public double getPerimeter();
}

An interface in Java is a collection of abstract methods and constants that defines a contract between a class and the outside world. Interfaces allow for loose coupling between classes and enable a high degree of flexibility and modularity in Java code.

How to use the abstract Keyword in Java

The abstract keyword in Java is a non-access specifier that can be used to define both abstract methods and abstract classes. Note that, while you can apply the abstract keyword on classes and methods, you cannot use this keyword on variables or objects.

How to use the extends Keyword in Java

Programmers can take advantage of the extends keyword in Java to create a subclass that inherits behavior and characteristics from a Superclass. To use the extends keyword, create a parent class and then create a subclass that extends the parent class to inherit members from the parent class except those that are private.

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Benefits of Abstraction in Java

Abstraction in Java provides developers several benefits:

• Encapsulation: Abstraction helps encapsulate the complexity of a system by exposing only the necessary features and behavior, making the system easier to use and maintain.
• Flexibility: Abstraction promotes flexibility and extensibility in software designs. Adding new features to a system is easier because the interface remains the same, and the implementation details can be hidden behind it.
• Maintainability: Abstraction helps to reduce code duplication by providing a way to define common behavior in a single location.
• Polymorphism: Abstraction allows for polymorphism by providing a way for multiple classes to implement the same interface, even if they have different implementations for the methods defined in the interface.

Disadvantages of Abstraction

Despite the benefits, there are certain downsides to Java abstraction as well:

• Complexity: Abstraction can add complexity to the code, especially when there are many layers of abstraction, making it harder to understand and maintain.
• Performance: Abstraction can come at a performance cost, as there may be extra overhead involved in providing a common interface and hiding implementation details.
• Over-Engineering: Abstraction can also lead to over-engineering if not properly designed, leading to unnecessary complexity and increased development time.
• Learning Curve: Abstraction requires a certain level of knowledge and understanding, which can make it difficult for beginners to grasp the concepts and write effective code.

Best Practices for Abstraction in Java

Here are some best practices for abstraction in Java, including using meaningful names, extension design, following the Liskov Substitution Principle, avoiding leaky abstractions, and refactoring your abstraction:

• Keep it simple: Abstraction is meant to simplify code, not make it more complex. Avoid over-engineering and creating unnecessary abstraction layers that add complexity without adding any value.
• Focus on the essential: Abstraction should focus on the essential parts of the system, while hiding implementation details that are not relevant to the user. Identify the core features and behaviors that need to be exposed, and abstract them out.
• Use meaningful names: Use meaningful names for abstract classes, methods, and interfaces. Names should be self-explanatory and clearly indicate the purpose and behavior of the abstraction.
• Design for extension: When designing an abstraction, consider how it will be extended in the future. Use the Open-Closed Principle to ensure that the abstraction is open for extension but closed for modification.
• Follow the Liskov Substitution Principle: Any implementation of an abstraction should be a valid substitute for the abstraction. This means that it should provide the same behavior and features as the abstraction.
• Avoid leaky abstractions:, A leaky abstraction is one that exposes too much implementation detail to the user, breaking the abstraction. Ensure that abstractions are complete and do not leak implementation details.
• Test abstraction: When testing code that uses an abstraction, ensure that it behaves correctly according to the abstraction’s contract. Write tests that cover the expected behavior of the abstraction.
• Refactor abstraction when necessary: Abstractions should evolve as the system evolves. To maintain relevance and to meet the changing requirements of the system as time goes on, abstractions should be refactored when necessary.

Final Thoughts on Java Abstraction

Abstraction is a powerful tool for simplifying code, enhancing maintainability, and promoting code reuse. It helps in creating modular and flexible code, by reducing the complexity of the system, making it easy to maintain, test, debug and update.

Despite the benefits, abstraction can also lead to over-engineering, add complexity to the code, and impact performance. It’s important to use abstraction judiciously and strike a balance between the benefits and downsides to achieve optimal results.

Read: Tips to Improve Performance in Java