What is aggregation?

Question Posted / jyotishankar

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What is aggregation?..

Answer / bnaga

# Aggregation: If class have an entity reference,it is known as Aggregation. Aggregation represents HAS-A relationship.
Suppose.
Let suppose person have lots of information like name, address,phone number , id , education. so here we can further divide education in parts of education like
1)Post graduation
2)Graduation
3)Senior secondary
4)Higher secondary
in this case person have entity reference education

For example:

/*
class Person{
String name;
int id;
int Monumber;
String educatoin//entity refrence

}
*/

Why we use Aggregation : for code reusability in program.

By example :

Education.java
/*
public class Education {
String postgraduation,gradution,seniorsecondary,highersecondary;

public Education(String postgraduation,
String gradution,String seniorsecondary,String highersecondary) {

this.postgraduation = postgraduation;
this.gradution = gradution;
this.seniorsecondary = seniorsecondary;
this.highersecondary = highersecondary;
}

}

*/

Persona.java
/*
class Person{
String name;
int id;
Education edu; // entity reference

Person( String name, int id, Education edu){

this.name = name;
this.id = id;
this.edu = edu;
}

void showdata(){

System.out.println("Name:="+name+"Id:="+id);
System.out.println(edu.postgraduation+""+ edu.gradution+""+edu.seniorsecondary+""+edu.highersecondary)
}
public static void main(String args[]){
Education ed1 = new Education("MSC","BSC","10th","12th");
Education ed2 = new Education("MSC","BSC","10th","12th");

Person p1 = new Person("Bang",1,ed1);
Person p2 = new Person("Babu",2,ed2);

p1.showdata();
p2.showdata();

}
}
*/

Aggregatoin(HAS-A) is better than Composition(IS-A) relationship.

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