Abstract Classes in Java

        

          

            

              
              

          
 
          

          
          

          

              

                  
              

          








Introduction to Abstract Classes in Java



Abstract classes in Java are classes that cannot be instantiated directly. They must be extended by other classes, which are known as subclasses. Abstract classes can contain both abstract and non-abstract methods. Abstract methods are methods that do not have an implementation in the abstract class. Subclasses must provide their own implementations for abstract methods.



Abstract classes are used to provide a common functionality for a group of related classes. For example, you could create an abstract class called `Animal` that contains abstract methods such as `eat()` and `sleep()`. Then, you could create subclasses of `Animal` such as `Dog`, `Cat`, and `Bird`. Each subclass would provide its own implementation for the abstract methods in the `Animal` class.



Here is an example of an abstract class in Java:



public abstract class Animal {
  public abstract void eat();
  public abstract void sleep();
}




Here is an example of a subclass of the `Animal` class:



public class Dog extends Animal {
  @Override
  public void eat() {
    System.out.println("The dog is eating.");
  }

  @Override
  public void sleep() {
    System.out.println("The dog is sleeping.");
  }
}




Abstract classes can be a very useful tool for organizing your code and making it more reusable. However, it is important to use them carefully. If you overuse abstract classes, your code can become difficult to read and maintain.



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



    
  
  • Improved code organization: Abstract classes can help you to organize your code into a hierarchy of related classes. This can make your code more readable and maintainable.
    • 
  
  • Increased code reusability: Abstract classes can help you to write more reusable code by allowing you to define common functionality for a group of related classes.
    • 
  
  • Reduced errors: Abstract classes can help to reduce errors in your code by preventing you from instantiating classes that are not meant to be instantiated directly.
    • 




Overall, abstract classes are a powerful tool that can help you to write more organized, reusable, and reliable Java code.



Here are some tips for using abstract classes effectively:



    
  
  • Use abstract classes to provide a common functionality for a group of related classes.
    • 
  
  • Be careful not to overuse abstract classes, as this can make your code difficult to read and maintain.
    • 
  
  • Document the reasons for using abstract classes in your code.
    • 




If you are working with Java, I encourage you to learn more about abstract classes and how to use them effectively.







  


Exercises


Demo code for creating an object for a class that inherits an abstract class in Java



  package javaprogrammingdemo;
  public class javalabclass {
  
    public static void main(String[] args) {
      //cannot instantiate an abstract class
      //constructors are allowed for an abstract class
      //final methods are allowed 
      square s = new square(2);
      s.calculate_area();
      s.display_area();
      square.test();
    }	
  }
  
  //an abstract class is given below
  abstract class shape
  {
    float area;
    public shape() {
      this.area=0.0F;
    }
    //abstract method declaration
    abstract public void calculate_area();
    public static void test()
    {
      System.out.println("hello from static method");
    }
    public final void display_area()
    {
      System.out.println(area);
    }
  }
  
  //extending the abstract class.
  class square extends shape
  {
    int side;
    public square(int side) {
      this.side = side;
    }	
    //implementing the abstract method 
    //its mandatory to provide the implementation of the 
    //abstract methods inherited.
    public void calculate_area() {
      this.area=side*side;
    }
  }