Notes

Facade:
public class FacadePatternDemo {
public static void main(String[] args) {
ShapeMaker shapeMaker = new ShapeMaker();

shapeMaker.drawCircle();
shapeMaker.drawRectangle();
shapeMaker.drawSquare();
}
}

interface Shape {
void draw();
}

class Circle implements Shape {

@Override
public void draw() {
System.out.println("Circle::draw()");
}
}

class Square implements Shape {

@Override
public void draw() {
System.out.println("Square::draw()");
}
}

class Rectangle implements Shape {

@Override
public void draw() {
System.out.println("Rectangle::draw()");
}
}

class ShapeMaker {
private Shape circle;
private Shape rectangle;
private Shape square;

public ShapeMaker() {
circle = new Circle();
rectangle = new Rectangle();
square = new Square();
}

public void drawCircle(){
circle.draw();
}
public void drawRectangle(){
rectangle.draw();
}
public void drawSquare(){
square.draw();
}
}


Restaurant:
import java.util.ArrayList;
import java.util.List;


public class RestaurantOrderSystem {
public static void main(String[] args) {
Chef chef = new Chef();

Command burgerCommand = new BurgerCommand(chef);
Command pizzaCommand = new PizzaCommand(chef);

Waiter waiter = new Waiter();
waiter.takeOrder(burgerCommand);
waiter.takeOrder(pizzaCommand);
waiter.submitOrders();
}
}


class Chef {
public void makeBurger() {
System.out.println("Chef is making a burger.");
}
public void makePizza() {
System.out.println("Chef is making a pizza.");
}
}


interface Command {
void execute();
}


class BurgerCommand implements Command {
private Chef chef;
public BurgerCommand(Chef chef) {
this.chef = chef;
}

@Override
public void execute() {
chef.makeBurger();
}
}


class PizzaCommand implements Command {
private Chef chef;
public PizzaCommand(Chef chef) {
this.chef = chef;
}

@Override
public void execute() {
chef.makePizza();
}
}


class Waiter {
private List<Command> orders = new ArrayList<>();
public void takeOrder(Command command) {
orders.add(command);
}

public void submitOrders() {
for (Command command : orders) {
command.execute();
}
orders.clear();
}
}

Observer:
import java.util.ArrayList;
import java.util.List;


interface Subject {
void registerObserver(Observer observer);
void removeObserver(Observer observer);
void notifyObservers(String post);
}


class FacebookUser implements Subject {
private String username;
private List<Observer> followers;
private String latestPost;

public FacebookUser(String username) {
this.username = username;
this.followers = new ArrayList<>();
}

public void postUpdate(String post) {
latestPost = post;
notifyObservers(post);
}

@Override
public void registerObserver(Observer observer) {
followers.add(observer);
}

@Override
public void removeObserver(Observer observer) {
followers.remove(observer);
}

@Override
public void notifyObservers(String post) {
for (Observer follower : followers) {
follower.update(username, post);
}
}
}


interface Observer {
void update(String username, String post);
}


class FacebookFollower implements Observer {
private String followerName;

public FacebookFollower(String followerName) {
this.followerName = followerName;
}

@Override
public void update(String username, String post) {
System.out.println(followerName + " received an update from " + username + ":");
System.out.println(post);
System.out.println();
}
}

public class ObserverPatternDemo {
public static void main(String[] args) {

FacebookUser alice = new FacebookUser("Alice");
FacebookUser bob = new FacebookUser("Bob");


FacebookFollower follower1 = new FacebookFollower("Follower 1");
FacebookFollower follower2 = new FacebookFollower("Follower 2");


alice.registerObserver(follower1);
alice.registerObserver(follower2);
bob.registerObserver(follower2);


alice.postUpdate("Hello, everyone! This is my first post.");
bob.postUpdate("Feeling excited about the weekend!");


alice.removeObserver(follower1);


alice.postUpdate("A beautiful sunset today!");


}
}