Inheritance.MD

INHERITANCE

Inheritance is a procedure in which a object acquires all the properties and behaviours of a parent object.

Inheritance is a propety of inheriting all the properties and the behaviour from the parent class into child class.

Terms used in Inheritance :

• Class: It is template from which object is created.
• Sub-Class : Child Class.
• Super-Class : Parent Class.
• Code resuability : It is a mechanism that faciliates to reuse the methods and fields of the existing class when the new class is created.

NOTE :

• Inheritance is being achieved by extends keyword.
• Some of the properties cannot be inherited.

Importance of Inheritance :

• Code Resuability.
• We can achieve polymorphism by inheritance.

Disadvantages :

• Every code is been tightly coupled if we change in the parent class then the whole code will be effected.

Syntax :

class Animal{
    void eat(){
        System.out.println("I am eating");
    }
}

class Dog extends Animal{
    public static void main(String[] args){
        Dog d = new Dog();
        d.eat();
    }
}

Output: I am eating

Here Dog IS-A relationship with Animal.

Types of Inheritance :

• Single Inheritance.
• Multi-level Inheritance.
• Hybrid Inheritance.
• Multiple Inheritance.
• Hierarchial Inheritance.

On the basis of classification Java supports only 3 inheritances Single, Multi-level, Hierarchial and the other two Multiple and Hybrid is been supported by interface only.

Single Inheritance

When a class inherits another class is called Single Inheritance.

class Animal{
    public void eat(){
        System.out.println("Eating");
    }
}

class Dog extends Animal{
    public void bark(){
        System.out.println("Barking");
    }
}

class Test{
    public static void main(String[] args){
        Dog d = new Dog();
        d.eat();
        d.bark();
    }
}

Output:
Eating
Barking

Multi-level Inheritance

When there is a chain of Inheritance is called Multi-level Inheritance.

class Animal{
    public void eat(){
        System.out.println("Eating");
    }
}

class Lion extends Animal{
    public void roar(){
        System.out.println("Roaring");
    }
}

class Cub extends Lion{
    public void weep(){
        System.out.println("Weeping");
    }
}

class multilevelinheritance{
    public static void main(String[] args){
        Cub Simba = new Cub();
        Simba.eat();
        Simba.roar();
        Simba.weep();
    }
}

Output:
Eating
Roaring
Weeping

Hierarchial Inheritance

When two or more classes inherits a single class is called Hierarchial Inheritance.

class Animal{
    public void eat(){
        System.out.println("Eating");
    }
}

class Dog extends Animal{
    public void bark(){
        System.out.println("Barking");
    }
}

class Cat extends Animal{
    public void meow(){
        System.out.println("Meowing");
    }
}

class hierarchialinheritance{
    public static void main(String[] args){
        Cat yu = new Cat();
        yu.eat();
        yu.meow();
        //yu.bark(); // Compile Time Error
    }
}

Multiple and Hybrid Inheritance can't be achieved by the Java classes it can only be possible by the Java interfaces.

Multiple Inheritance

When a class can inherit more than one classes.

In java it means a class cannot extend more than one classes.However, a class can implement more than one or more interfaces from which we can get rid of the impossibility of the Multiple Inheritance.

Hybrid Inheritance

It is a combination of more than one types of inheritances.

We can achieve thorugh Java Classes.

UPDATE WITH IMAGES

         C
         ↑
         |
  ---------------
  ↑             ↑
  |             |
  A             B
  ↑
  |
  D

Explanation :
Class A and B extends class C → Hierarchical inheritance
Class D extends class A → Single inheritance

class C{
   public void disp(){
	System.out.println("C");
   }
}

class A extends C{
   public void disp(){
	System.out.println("A");
   }
}

class B extends C{
   public void disp(){
	System.out.println("B");
   }
}

class D extends A{
   public void disp(){
	System.out.println("D");
   }
   public static void main(String args[]){
	D obj = new D();
	obj.disp();
   }
}

Output:
D

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Why there is no hybrid inheritance in java?

Java supports hybrid inheritance. However, Java doesn't support Multiple Inheritance classes, so in order to achieve hybrid inheritance, multiple inheritances with classes should not be used. Multiple Inheritance with Interfaces is possible.

Why pointers are not used in Java

Java is a highly secured programming language. Pointers provide direct access to a memory address, and an arbitrary memory location can be accessed, and read and write operations can be performed on it. For the purpose of security Java does not support Pointers.

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