Abstract Class Program in Java

Last Updated on April 26, 2023 by Prepbytes

Java is an object-oriented programming language that allows you to create classes and objects that can be used to model real-world entities and concepts. One of the key features of Java is the ability to create abstract classes, which are classes that cannot be instantiated but provide a base for other classes to extend and inherit common properties and methods. Here, we’ll explore the abstract class program in Java and see how it can be used to improve the design and structure of your code.

What is an Abstract Class in Java?

An abstract class in Java is a class that is declared with the abstract keyword. It is a class that cannot be instantiated, meaning you cannot create objects of an abstract class directly. Instead, it serves as a blueprint or a template for other classes to extend from. Abstract classes are used to define the common characteristics and behaviors of a group of related classes, and they can contain both abstract and non-abstract methods.

An abstract method is a method that is declared without any implementation. It is used to declare a behavior that must be implemented by any class that extends the abstract class. Abstract methods are defined using the abstract keyword, and they do not have a body. Any class that extends the abstract class must implement all of its abstract methods, or it will also be declared as an abstract class.

An abstract class may contain non-abstract methods as well. These methods have a body, and they are used to provide a default implementation of behavior that can be overridden by any class that extends the abstract class.

Examples of Abstract Class Program in Java

Here are some examples of abstract class program in Java:

Example 1 of Abstract Class Program in Java: Shape Class
The Shape class is a classic example of an abstract class in Java. It provides a base class for different types of shapes, such as circles, squares, and triangles.

Code:

abstract class Shape {
    private int x;
    private int y;

    public Shape(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public abstract double getArea();
    public abstract double getPerimeter();

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }
}

In this example, the Shape class is declared as abstract using the abstract keyword. It has two instance variables x and y, and a constructor that initializes these variables. The Shape class also has two abstract methods getArea() and getPerimeter(), which are used to calculate the area and perimeter of the shape. These methods do not have any implementation in the Shape class, but they must be implemented by any subclass that extends the Shape class.

Example 2 of Abstract Class Program in Java: Animal Class
The Animal class is another example of an abstract class in Java. It provides a base class for different types of animals, such as cats, dogs, and birds.

Code:

abstract class Animal {
    private String name;

    public Animal(String name) {
        this.name = name;
    }

    public abstract String getSound();

    public String getName() {
        return name;
    }
}

In this example, the Animal class is declared as abstract using the abstract keyword. It has an instance variable name and a constructor that initializes this variable. The Animal class also has an abstract method getSound(), which is used to get the sound that the animal makes. This method does not have any implementation in the Animal class, but it must be implemented by any subclass that extends the Animal class.

Advantages of Abstract Class Program in Java

Here are some of the benefits of using abstract classes in Java:

• Code reusability: Abstract classes in Java can be used to define a common interface for a group of related classes, which helps to avoid code duplication and makes your code more organized and easier to maintain.
• Polymorphism: Abstract classes allow for polymorphism, which is the ability of objects to take on many different forms. By creating a hierarchy of classes that share common characteristics and behaviors, you can create objects that can be used interchangeably with other objects in the hierarchy.
• Flexibility: Abstract classes provide a flexible way to create new classes that share common characteristics and behaviors. By defining these characteristics and behaviors in an abstract class, you can easily create new classes that extend the abstract class and inherit its properties and methods.

Conclusion
In this article, we’ve explored abstract class program in Java and seen how they can be used to define a common interface for a group of related classes. We’ve also seen how abstract classes can be extended and used in your code to provide code reusability, polymorphism, and flexibility. By using abstract classes in your Java code, we can create more organized, maintainable, and flexible code that is easier to work with and understand.

Frequently Asked Questions(FAQs)

Here are some frequently asked questions on the abstract class program in Java.

Ques 1. Can you instantiate an abstract class in Java?
Ans. No, you cannot instantiate an abstract class in Java. You must first create a subclass that extends the abstract class and implements all the abstract methods.

Ques 2. Can an abstract class have a constructor?
Ans. Yes, an abstract class can have a constructor. However, it cannot be used to create objects of the abstract class, only objects of its subclasses.

Ques 3. Can an abstract class have non-abstract methods?
Ans. Yes, an abstract class can have both abstract and non-abstract methods.

Ques 4. Can an abstract class be final?
Ans. No, an abstract class cannot be final because it is intended to be a base class for other classes to inherit from.

Ques 5. Can an abstract class be private or protected?
Ans. No, an abstract class cannot be private because it is intended to be a base class for other classes to inherit from. It can be protected, but this is not common practice.