Java inheritance

Usage of inheritance in Java

• Code Reusability: All subclasses share the code written in the Superclass. The parent class code can be used directly by child classes.
• Method Overriding:Only inheritance allows for Method Overriding. It is one method for achieving Run Time Polymorphism in Java.
• Abstraction:Inheritance allows us to achieve the concept of abstraction, where we are not required to provide all the details. Abstraction only makes the user aware of the functionality.

Important Terms used in Inheritance

• Class: A class is a collection of objects that have similar traits, behaviours, and attributes. Class does not exist in the real world. It simply serves as a model, blueprint, or prototype from which objects can be made.
• Super Class or Parent Class:A superclass is a class from which features are inherited
• Sub Class or Child Class:A subclass is a class that inherits from another class (or a derived class, extended class, or child class). In addition to the fields and methods of the superclass, the subclass may also add additional fields and methods.
• Reusability:The idea of "reusability" is supported by inheritance; for example, if we want to create a new class but an existing class already contains some of the code we need, we can derive our new class from the existing class. We are utilising the fields and methods of the pre-existing class by doing this.

Fact about Java inheritance

• Default superclass: Every class, with the exception of the Object class, has a single direct superclass (single inheritance). Every class is implicitly a subclass of the Object class in the absence of any other explicit superclass.
• Only one Superclass:Any number of subclasses can exist under a superclass. But there can only be one superclass per subclass. This is due to Java's lack of support for multiple class inheritances. Java does support multiple inheritances, but only with interfaces.
• Inherite Constructors:Fields, methods, and nested classes are all members that a subclass inherits from its superclass. Subclasses cannot inherit constructors because they are not members; however, they may call the constructor of the superclass.
• Inheritance with Private member :The private members of a parent class are not inherited by a subclass. However, the subclass may also use the public or protected methods that the superclass provides (such as getters and setters) to access its private fields.

The syntax of Java Inheritance

• Java uses the extends keyword to describe inheritance. When you use the extends keyword, it shows that you are a derived class. In other words, "extends" means that the functionality has been increased.

Syntax

 class  Subclass-name extends   Superclass-name   

     statements;  

  } 

Types of inheritance in java

• In Java, there are three different types of inheritance that can be used:
  • single inheritance
  • multilevel inheritance
  • hierarchical inheritance
• Multiple and hybrid inheritance are only supported through interfaces in Java programming.

1.Single Inheritance

Subclasses inherit the characteristics of a single superclass under single inheritance.

Java program with single inheritance

 // Java program with single inheritance  

class Shape{  
    void Draw(){
        System.out.println("Drawing...");
    }  
 }  
  class Circle extends Shape{ 
      void CircleDraw(){
          System.out.println("Circle Drawing....");
      }
 }  
  class Inheritance{  
      public static void main(String args[]){  
          Circle Circle=new Circle(); 
          Circle.Draw(); 
          Circle.CircleDraw();  	
      }
 }
  

Drawing... 

 
 Circle Drawing.... 

2.Multilevel Inheritance

A derived class will inherit a base class in multilevel inheritance, and in addition, the derived class will serve as the base class for other classes.

Java program with Multilevel inheritance

 // Java program with Multilevel inheritance 

class Shape{  
    void Draw(){
        System.out.println("Drawing...");
    }  
  }  
  class Circle extends Shape{ 
      void CircleDraw(){
          System.out.println("Circle Drawing....");
      }
  }  
  class SemiCircle extends Circle{ 
      void SemiCircleDraw(){
          System.out.println("Semicircle Drawing....");
      }
  }
  class Inheritance{  
      public static void main(String args[]){  
          SemiCircle semiCircle=new SemiCircle(); 
          semiCircle.Draw(); 
          semiCircle.CircleDraw();
          semiCircle.SemiCircleDraw();
      }
  }
  

Drawing... 

 
 Circle Drawing.... 

 
 Semicircle Drawing.... 

3.Hierarchical Inheritance

One class acts as the superclass (base class) for multiple subclasses in hierarchical inheritance.

Java program using hierarchical Inheritance

 // Java program  using hierarchical Inheritance 

class Shape{  
    void Draw(){
        System.out.println("Drawing...");
    }  
  }  
  class Circle extends Shape{ 
      void CircleDraw(){
          System.out.println("Circle Drawing....");
      }
  }  
  class SemiCircle extends Shape{ 
      void SemiCircleDraw(){
          System.out.println("Semicircle Drawing....");
      }
  }
  class Inheritance{  
      public static void main(String args[]){  
          SemiCircle semiCircle=new SemiCircle(); 
          semiCircle.Draw(); 
  //		semiCircle.CircleDraw();    //Compile Time Error
          semiCircle.SemiCircleDraw();
      }
  }
  

Drawing... 

 
 Semicircle Drawing.... 

4.Multiple Inheritance in java using Interfaces

A class can have more than one superclass and receive features from all of its parent classes when there are multiple inheritances. Please be aware that multiple inheritances with classes are not supported by Java. Only by using interfaces in Java is multiple inheritance possible.

Java program Multiple Inheritance using Interfaces

 // Java program Multiple Inheritance using Interfaces 

  import java.util.*;

    interface  Shape{  
        public void Draw(); 
    }  
    interface  Circle extends Shape{ 
        public void CircleDraw();
    }  
    interface  SemiCircle extends Circle, Shape{ 
        public void SemiCircleDraw();
    }
    class Test implements SemiCircle {
    
        @Override
        public void CircleDraw() {
            System.out.println("Circle Drawing....");		
        }
        @Override
        public void Draw() {
            System.out.println("Drawing....");	
        }
        @Override
        public void SemiCircleDraw() {
            System.out.println("Semi Circle Drawing....");	
        }
    }
    
    class Inheritance{  
        public static void main(String args[]){  
            Test test=new Test(); 
            test.Draw(); 
            test.CircleDraw();   
            test.SemiCircleDraw();
        }
    }
    

Drawing... 

 
 Circle Drawing.... 

 
 Semicircle Drawing.... 

5.Hybrid Inheritance using Interfaces

It combines two or more of the already defined inheritance patterns. Hybrid inheritance is not possible with classes because Java does not support multiple inheritances. Only by using interfaces in Java is hybrid inheritance possible.