# HAS-A Relationship

## Introduction 
1. While developing applications we do not code from scratch,Instead we enhance the already available code
2. For this we use a relationship
  Advantages Of Using Relationship
  a. Optimisation Of Code
  b. Code Reusability
  c.  Execution Time

## Types Of Relationship
1. IS-A
2. HAS-A
IS-A relationship basically implies inheritance using extends keyword

##  HAS-A
1. It defines an association between two entities/classes
2. This helps in communication and data transfer between two entities/classes.
3. In Java we have 4 types of association

a. one to one
b. one to many
c. many to many
d. many to one

## How to achieve association
1. To achieve association between two entities we have to display either a single reference or an array  of reference in other class entities
  

## Key Terms In HAS A relationship
1.  Dependency Injection:   The process of inserting the dependent object into target object is called dependency injection

2. Target Object: The object which is given to the developer to the user is called as the target object
3. Dependent Object:   The object that helps the target object is called a a dependent object

Note 1. The object which helps is the dependent object
           2. The object who needs help is the target object

example: student object needs the address object
student object is the target object
address object is the dependent object 

## How to perform dependency injection 
1. This can be done through constructor
2. Through settter