Objects & Relations: Three most common relationships among classes in Java:
Use-A relation: When we create an object of a class inside a method of another class, this relationship is called dependence relationship in Java, or simply Uses-A relationship.
| BankEmployee use Customer Account objects to perform their transactions |
Is-A relation: Is-A relationship defines the relationship between two classes in which one class extends another class.
| Every Employee is a Person Every Manager is an Employee |
Has-A relation: When an object of one class is created as data member inside another class, it is called association relationship in java or simply Has-A relationship.
| Every Person object Has Address object |
There are two types of Has-A relationship that are as follows:
Aggregation :
- Establish a weak Has-A relation between objects.
- For example, Library Has Students.
- If we destroy Library, Still student objects alive.
Composition :
- Establish a Strong Has-A relation between objects.
- For example, Person Has Aadhar.
- If the Person died, Aadhar will not work there after.