Hi Dinesh pun,
Inheritance and Aggregation are used for code re-usability. But both have slightly different purpose of usability. It's depend on you which one better to use.
Inheritance is 'is a' relationship while Aggregation is 'has a' relationship base usage.
For example, i) suppose you have Wheel class
public class Wheel
and want to use in Car class then you don't have Car extend Wheel. Car has wheels. In this case you have to use aggregation as:
public class Car
// other memebers
ii) suppose you have Vehicle class then you can inherit to new class Car as Car is a vehicle:
public class Vehicle
public class Car : Vehicle
// inherits Vehicle properties and methods