Example programs on Fly Weight Design pattern : Student marks list

//Extrinsic.java
package com.demo;

public interface Extrinsic {
String getDivision();

}

//ExtrinsicFactory.java

package com.demo;

import java.util.*;

public class ExtrinsicFactory {

public static Map<String, Extrinsic>m=new HashMap<String,Extrinsic>();

 public static int count;

 //static factorymethod that gives Extrinsic object by checking buffer/cache(m)

public static Extrinsic getExtrinsic(String division)

{

//here Fly Weight logic is implementing

if(m.containsKey(division))

{

Object o=m.get(division);

Extrinsic i=(Extrinsic)o;

return(i);

}

Extrinsic extr=new ExtrinsicFactory.ExtrinsicClass(division);

m.put(division,extr);

return(extr);

}//end of factory method

//inner class acting as Extrinsic class having logic to hold division

public static class ExtrinsicClass implements Extrinsic

{

private String division;

private ExtrinsicClass(String division)

{

this.division=division;

count++;

System.out.println("no.of Extrinsic object="+count);

}

public String getDivision()

{

return(division);

}

}//End of Extrinsic class

}//end of ExtrinsicFactory class

//ICard.java

package com.demo;

public class ICard 

{

//Intrinsic properties

 private String empname;

 private int empid;

 //Extrinsic properties

 private Extrinsic extr;

 public ICard(String empname, int empid, Extrinsic extr)

 {

this.empname=empname;

this.empid=empid;

this.extr=extr;

 

 }

 public void print()

 {

System.out.println("Emp name :"+empname);

System.out.println("Emp id :"+empid);

System.out.println("Division :"+extr.getDivision());

 

 }

}

//MainApp.java

package com.demo;

public class MainApp {

public static void main(String args[])

{

ICard ic1=new ICard("raj",111,ExtrinsicFactory.getExtrinsic("A"));

ICard ic2=new ICard("RAVI",222,ExtrinsicFactory.getExtrinsic("A"));

ICard ic3=new ICard("RAMESH",666,ExtrinsicFactory.getExtrinsic("B"));

ICard ic4=new ICard("RAMANA",999,ExtrinsicFactory.getExtrinsic("A"));

System.out.println("------------");

ic1.print();

System.out.println("------------");

ic2.print();

System.out.println("------------");

ic3.print();

System.out.println("------------");

ic4.print();

}

}

/*

 * output:

 * no.of Extrinsic object=1

no.of Extrinsic object=2

------------

Emp name :raj

Emp id :111

Division :A

------------

Emp name :RAVI

Emp id :222

Division :A

------------

Emp name :RAMESH

Emp id :666

Division :B

------------

Emp name :RAMANA

Emp id :999

Division :A

 */

This Buffer or cache development have Extrinsic Data is nothing but implementation of private Design pattern

Fly Weight Design Pattern

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