Java Abstraction

Abstract Classes and Methods

Abstract classes and methods are fundamental concepts in Java's object-oriented programming paradigm. They provide a way to define common behavior and enforce certain rules across a group of related classes. Here's an overview of abstract classes and methods:

Abstract Classes:

• An abstract class is a class that cannot be instantiated directly. It serves as a blueprint for other classes and may contain one or more abstract methods.
• Abstract classes may also include concrete methods (methods with a body) that provide default behavior or utility methods.
• Abstract classes are declared using the abstract keyword.

Example of an abstract class:

    public abstract class Shape {
        // Abstract method
        public abstract double area();
        
        // Concrete method
        public void display() {
            System.out.println("This is a shape.");
        }
    }
   

Abstract Methods:

• An abstract method is a method declared without a body. It must be implemented by any non-abstract subclass of the abstract class.
• Abstract methods are declared using the abstract keyword and do not have a method body.
• Abstract methods define a contract that subclasses must follow, ensuring that certain behavior is implemented in all concrete subclasses.

Example of an abstract method within the Shape class:

public abstract double area();

Creating Concrete Subclasses:

• Concrete subclasses of an abstract class must implement all abstract methods declared in the superclass.
• Failure to implement all abstract methods in a subclass results in a compilation error.

Example of a concrete subclass of the Shape class:

        public class Circle extends Shape {
            private double radius;
        
            public Circle(double radius) {
                this.radius = radius;
            }
        
            @Override
            public double area() {
                return Math.PI * radius * radius;
            }
        }
     

Benefits of Abstract Classes and Methods:

• Code Reusability: Abstract classes provide a common interface and behavior that can be shared among multiple subclasses.
• Contractual Obligation: Abstract methods define a contract that concrete subclasses must adhere to, ensuring consistency in behavior across subclasses.
• Abstraction: Abstract classes and methods promote abstraction by separating interface from implementation, allowing developers to focus on the "what" rather than the "how."