Types of Inheritance in Java

Posted on July 24, 2019
java
inheritance
57

Inheritance types:

On the basis of class, there can be three types of inheritance in java: single, multilevel and hierarchical.

In java programming, multiple and hybrid inheritance is supported through interface only.

Single Inheritance :

 In single inheritance, subclasses inherit the features of one superclass. In image below, the class A serves as a base class for the derived class B.

Single Inheritance Example:

//SingleInheritance.java

class Animal
{  
   void eat()
   {
      System.out.println("eating...");   
    }  
}  
class Dog extends Animal
{  
   void bark()
   {
      System.out.println("barking...");
   }  
}  
class SingleInheritance
{  
    public static void main(String args[])
    {  
       Dog d=new Dog();  
       d.bark();  
       d.eat();  
     }
}  

Multilevel Inheritance:

 In Multilevel Inheritance, a derived class will be inheriting a base class and as well as the derived class also act as the base class to other class. In below image, the class A serves as a base class for the derived class B, which in turn serves as a base class for the derived class C. In Java, a class cannot directly access the grandparent's members.
 

Multilevel Inheritance Example:

//MultilevelInheritance.java

class Animal
{  
  void eat()
  {
      System.out.println("eating...");
   }  
}  
class Dog extends Animal
{  
  void bark()
  { 
      System.out.println("barking...");
   }  
}  
class BabyDog extends Dog
{  
   void weep()
   {
      System.out.println("weeping...");
   }  
}  
class MultilevelInheritance
{  
     public static void main(String args[])
     {  
           BabyDog d=new BabyDog();  
           d.weep();  
           d.bark();  
           d.eat();  
     }
}  
 

Hierarchical Inheritance :

 In Hierarchical Inheritance, one class serves as a superclass (base class) for more than one sub class.

Hierarchical Inheritance Example:

//HierarchicalInheritance.java

class Animal
{  
    void eat()
    {
        System.out.println("eating...");
    }  
}  
class Dog extends Animal
{  
    void bark()
    {
        System.out.println("barking...");
    }  
}  
class Cat extends Animal
{  
    void meow()
    {
        System.out.println("meowing...");
    }  
}  
class HierarchicalInheritance
{  
    public static void main(String args[])
    {  
        Cat c=new Cat();  
        c.meow();  
        c.eat();  
    }
}  

Why multiple inheritance is not supported in java?

To reduce the complexity and simplify the language, multiple inheritance is not supported in java. 

Consider a scenario where A, B, and C are three classes. The C class inherits A and B classes. If A and B classes have the same method and you call it from child class object, there will be ambiguity to call the method of A or B class.

Since compile-time errors are better than runtime errors, Java renders compile-time error if you inherit 2 classes. So whether you have same method or different, there will be compile time error.

Example :

class A
{  
    void msg()
    {
        System.out.println("Hello");
    }  
}  
class B
{  
    void msg()
    {
        System.out.println("Welcome");
    }  
}  
class C extends A,B //suppose if it were
{
   
    public static void main(String args[])  
    {  
        C obj=new C();  
        obj.msg();//Now which msg() method would be invoked?  
    }  
}  

 




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