Core Java Design Pattern : Structural Pattern : Facade Design Pattern

• Facade Design Pattern
• Examples

Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.

Use the Facade pattern when

• you want to provide a simple interface to a complex subsystem. Subsystems often get more complex as they evolve.
• there are many dependencies between clients and the implementation classes of an abstraction. Introduce a facade to decouple the subsystem from clients and other subsystems, thereby promoting subsystem independence and portability.
• you want to layer your subsystems. Use a facade to define an entry point to each subsystem level

Structuring a system into subsystems helps reduce complexity. A common design goal is to minimize the communication and dependencies between subsystems. One way to achieve this goal is to introduce a facade object that provides a single, simplified interface to the more general facilities of a subsystem.

RoomType.java

package com.javaskool.model;

public enum RoomType {	
	SINGLE, DOUBLE;
}

Room.java

package com.javaskool.model;

public class Room {
	private int rno;
	private RoomType type;
	private boolean vacant;
	
	public int getRno() {
		return rno;
	}
	public void setRno(int rno) {
		this.rno = rno;
	}
	public RoomType getType() {
		return type;
	}
	public void setType(RoomType type) {
		this.type = type;
	}
	public boolean isVacant() {
		return vacant;
	}
	public void setVacant(boolean vacant) {
		this.vacant = vacant;
	}
		
	public Room(int rno, RoomType type, boolean vacant) {
		super();
		this.rno = rno;
		this.type = type;
		this.vacant = vacant;
	}
	public Room() {
		super();
		
	}
	@Override
	public String toString() {
		return rno+" "+type+" "+vacant;
	}
}

HotelSearchService.java

package com.javaskool.model;

import java.util.LinkedList;
import java.util.List;

public class HotelSearchService {
	private List<Room> rooms; 
	public HotelSearchService() {
	// TODO Auto-generated constructor stub
		rooms=new LinkedList<Room>();
	}
	public void addRoom(Room room){
		rooms.add(room);
	}
	public List<Room> search(RoomType rt){
		List<Room> searchList=new LinkedList<Room>();
		for(Room r:rooms)
			if(r.isVacant() && r.getType().equals(rt))
				searchList.add(r);
		return searchList;
	}
	public void reserve(int rno){
		for(Room r:rooms){
			if(r.getRno()==rno)
			{
				r.setVacant(false);
				return;
			}
		}
	}
}

HotelFacade.java

package com.javaskool.facade;
import java.util.List;

import com.javaskool.model.HotelSearchService;
import com.javaskool.model.Room;
import com.javaskool.model.RoomType;

public class HotelFacade {
	HotelSearchService service;
	
	public HotelFacade() {
		super();
		service=new HotelSearchService();
		for(int i=0;i<20;i++)
			if(i%2==0)
				service.addRoom(new Room(i+1,RoomType.SINGLE,true));
			else
				service.addRoom(new Room(i+1,RoomType.DOUBLE,true));		
	}

	public String reserve(RoomType rt){//choice from reception
		List<Room>r=service.search(rt);
		if(r.size()>0)
		{
			
			service.reserve(r.get(0).getRno());
			return "success";
		}
		else
			return "failure";
		
	}
	public String reserve(RoomType rt, int i){//choice from customer
		List<Room>r=service.search(rt);
		if(r.size()>0)
		{
			
			service.reserve(i);//r.get(0).getRno());
			return "success";
		}
		else
			return "failure";
		
	}
	public void displayAvailableRooms(){
		System.out.println(service.search(RoomType.SINGLE));
		System.out.println(service.search(RoomType.DOUBLE));		
	}
}

TestDrive.java

package  com.javaskool;

import java.util.Scanner;

import com.facade.HotelFacade;
import com.model.RoomType;

public class TestDrive {
	public static void main(String arg[]){
		
		HotelFacade facade=new HotelFacade();
		facade.displayAvailableRooms();
		
		//Automatically from facade
		System.out.println(facade.reserve(RoomType.DOUBLE));

		//For Customer Choice
		/*Scanner sc=new Scanner(System.in);
		System.out.println("Enter Room No :");
		int i=sc.nextInt();
		System.out.println(facade.reserve(RoomType.SINGLE,i));*/
		
		//System.out.println(facade.reserve(RoomType.DOUBLE));
		System.out.println(facade.reserve(RoomType.SINGLE));		
		facade.displayAvailableRooms();		
	}
}

Output

c:\>javac -d . *.java
c:\>java com.javaskool.TestDrive

[1 SINGLE true, 3 SINGLE true, 5 SINGLE true, 7 SINGLE true, 9 SINGLE true, 11 SINGLE true, 13 SINGLE true, 15 SINGLE true, 17 SINGLE true, 19 SINGLE true]
[2 DOUBLE true, 4 DOUBLE true, 6 DOUBLE true, 8 DOUBLE true, 10 DOUBLE true, 12 DOUBLE true, 14 DOUBLE true, 16 DOUBLE true, 18 DOUBLE true, 20 DOUBLE true]
success
success
[3 SINGLE true, 5 SINGLE true, 7 SINGLE true, 9 SINGLE true, 11 SINGLE true, 13 SINGLE true, 15 SINGLE true, 17 SINGLE true, 19 SINGLE true]
[4 DOUBLE true, 6 DOUBLE true, 8 DOUBLE true, 10 DOUBLE true, 12 DOUBLE true, 14 DOUBLE true, 16 DOUBLE true, 18 DOUBLE true, 20 DOUBLE true]

UML Diagram for Hotel room Service Application having Implementation of Facade Design Pattern

Download:

Facade Design Pattern Code (11 KB)