Learn Inheritance and Constructor in Typescript- Day 10

 In this article, We are learn Inheritance and Constructor.

Inheritance:

•  TypeScript supports the concept of Inheritance.
• Inheritance is the ability of a program to create new classes from an existing class. 
• The class that is extended to create newer classes is called the parent class/super class.
•  The newly created classes are called the child/sub classes.
• A class inherits from another class using the ‘extends’ keyword. 
• Child classes inherit all properties and methods except private members and constructors from the parent class.
• There are 5 types of inheritance:

         1.Single Inheritance

         2.Multilevel Inheritance

         3.Multiple Inheritance

         4.Hybrid Inheritance

         5.Hierarchical Inheritance

• Syntax:

class child_class_name extends parent_class_name

Why use inheritance?

• We can use it for Method Overriding (so runtime polymorphism can be achieved).
• We can use it for Code Reusability.

 

Note: TypeScript supports only single and multilevel inheritance. It doesn't support multiple, hierarchical, and hybrid inheritance.

1.Single Inheritance

• Single inheritance can inherit properties and behavior from at most one parent class. 
• It allow a derived/subclass to inherit the properties and behavior of a base class that enable the code reusability as well as we can add new features to the existing code.

2.Multilevel Inheritance

• When a derived class is derived from another derived class, then this type of inheritance is known as multilevel inheritance.
•  Thus, a multilevel inheritance has more than one parent class.

Example:

Access Modifiers:

• The access modifiers are used for controlling the visibility or availability of its data members.
• There are three types of access modifiers in TypeScript: public, private and protected.

1.Public - 

• By default members (properties and methods) of TypeScript class are public - so you don’t need to prefix members with the public keyword. 
• Public members are accessible everywhere without restrictions.

 2.Private -

• A private member cannot be accessed outside of its containing class.
•  Private members can be accessed only within the class.

3.Protected -

• A protected member cannot be accessed outside of its containing class. P
• Protected members can be accessed only within the class and by the instance of its sub/child class.

Example of Access Modifier:

Constructor:

• In TypeScript, the constructor method is always defined with the name "constructor".
• Constructors are identified with the keyword "constructor". 
• A Constructor  is a  special type of method of a class and it will be automatically invoked when an instance of the class is created. 
• A class may contain at least one constructor declaration. 
• If a class has no constructor, a constructor is provided automatically. 
• A Class can have any number of constructors. 
• When you are using the attribute public or private with constructor parameters, a field is automatically created, which is assigned the value.

• Syntax :

           constructor () {

          // statement

            }                

   Example:                       

Thank you.....