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Association in Java Programming

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Generalization in java with examples

Generalization basic points

 Type/Subtype Relationship "IS A " Relationship One class has many subclasses  General class can have many Special classes as  subclasses General names can be used to Address special names Top to bottom hierarchy goes towards specialization Bottom to top Hierarchy goes towards generalization

e.g         Soap  
  Bath Soap and Washing Soap is a subclass of Soap

e.g COldDrink
  Pepsi      Team

-Cold Drink is a general class
-Pepsi and team are special classes

e.g    Person

Teacher       Student
e.g            Car
    Sedan           Hatchback
Honda   Suzuki     Suzuki   Toyota
civic        Liana      Alto      vitz
Some Examples from Nature

e.g.               Animal
           Mammals            Reptiles 

  Human           Cow     Snake         Croc

Student Teacher             Cobra Python    

e.g                     Fruits
     Mango       Orange       Banana     Strawberry

Some Examples from Kitchen

e.g             C…

Aggregation in java with example codes

What is aggregation? 
 "Have a" or "May have" relationship Aggregation is special type of association Life time of Component object is independent from its  container objectE.g A school has one student

class Student {
String name;
Student () {name=null; }
Student (String n) {name=n; }
void setName(String n) {name=n;}
String getName() { return name;}
class School{
Student  st;
School (  ) { st=null;}
School (Student s){st=s;}
void studentName(){
class Post{
public static void main (String a[]){
Student st=new Student("Imran");
School s= new School(st);


Problem : A Car must has Engine and body.
          A Car may or may not has Ac

Adding Ac as an Aggregate object in car

class Engine{
void start() {
System.out.println("Engine Start");
class Body{
void type() {
System.out.println("Saloon Type");
class Ac{
void cool() {
System.out.println("Super Cool");

class Car{
Engine e;
Body b;
Ac ac;

Composition in Java with code examples


"Have a " Relationship  OR  "Must have" relationship                    between two or more classes.Container class contains component's class objectFor example a  Car is composed of engine and body. Where Car is a container class and both Engine and Body are components class. Life Time Issue in Composition

Life time of component objects depends on container classIf Container object destroyed, component objects will be also destroyed

Car Example 

There is a composition relationship between car's body and engine.Car must have Engine and bodyIf Car destroyed, both Engine and Body will be destroyed

class Engine{Engine () {   System.out.println("Engine created");}void start() {System.out.println("Engine Start");}}class Body{Body () {System.out.println("Body created");}void type() {System.out.println("Saloon Type");}}class Car{Engine e;Body   b;Car () { e=new Engine();b= new Body();System.out.println("Car cre…