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// Composite Design Pattern

// ========================

// The Composite pattern lets clients treat individual objects and compositions

// of objects uniformly.

// Structure

// ---------

// The Composite pattern consists of three types of objects: the component,

// the leaf, and the composite. A component declares the interface for objects

// in the composition, and implements default behavior for the interface common

// to all classes, as appropriate. The base Component class can declare an

// interface for accessing and managing its child components. (optional)

// A leaf represents the end objects of a composition. A leaf has no children.

// It defines behavior for primitive objects in the composition. A composite

// defines behavior for components having children. It stores child components

// and implements child-related operations in the Component interface.

// Using the Composite pattern makes sense only when the core

// model of your app can be represented as a tree.

// Problem:

// --------

// Imagine that you are creating an online store. The store sells products

// and services. Each product or service can be sold individually or as part

// of a bundle. For example, a customer can buy a book, a music CD, and a

// video DVD as a bundle. The customer can also buy each of these items

// individually.

// The Composite pattern lets you treat individual objects and compositions

// uniformly. The client code can work with simple or complex elements without

// depending on their concrete classes.

import java.util.ArrayList;

import java.util.List;

// Component

public abstract class Product {

public abstract double getPrice();

}

// Leaf

public class Book extends Product {

private String title;

private double price;

public Book(String title, double price) {

this.title = title;

this.price = price;

}

public double getPrice() {

return price;

}

// Leaf

public class MusicCD extends Product {

private String title;

private double price;

public MusicCD(String title, double price) {

this.title = title;

this.price = price;

}

public double getPrice() {

return price;

}

// Leaf

public class VideoDVD extends Product {

private String title;

private double price;

public VideoDVD(String title, double price) {

this.title = title;

this.price = price;

}

public double getPrice() {

return price;

}

// Composite

public class Bundle extends Product {

private String name;

private List<Product> products = new ArrayList<>();

public Bundle(String name, Product... products) {

this.name = name;

for (Product product : products) {

this.products.add(product);

}

public void addProduct(Product product) {

products.add(product);

}

public void removeProduct(Product product) {

products.remove(product);

}

public double getPrice() {

double totalPrice = 0;

for (Product product : products) {

totalPrice += product.getPrice();

}

return totalPrice;

}

// Client code

public class OnlineStore {

public static void main(String[] args) {

Book book = new Book("The Lord of the Rings", 20.0);

MusicCD musicCD = new MusicCD("Abbey Road", 15.0);

VideoDVD videoDVD = new VideoDVD("The Godfather", 25.0);

Bundle bundle = new Bundle("Entertainment Bundle", book, musicCD, videoDVD);

System.out.println("Total price: " + bundle.getPrice());

}

// Use the Composite pattern only when your core model can be

// represented as a tree.

// Use the Composite pattern when you want clients to be able to

// ignore the difference between compositions of objects and individual

// objects. Clients will treat all objects in the composite structure

// uniformly.

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