Core Java Design Pattern : Creational Pattern :: Factory Design Pattern

• Factory Design Pattern?
• Examples

Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

Also Known As : Virtual Constructor

Use the Factory Method pattern when

• a class can’t anticipate the class of objects it must create.
• a class wants its subclasses to specify the objects it creates.
• classes delegate responsibility to one of several helper subclasses, and you want to localize the knowledge of which helper subclass is the delegate.

Application subclasses redefine an abstract CreateDocument operation on Application to return the appropriate Document subclass. Once an Application subclass is instantiated, it can then instantiate application-specific Documents without knowing their class. We call CreateDocument a factory method because it’s responsible for “manufacturing” an object

Pizza.java

package com.javaskool;

import java.util.ArrayList;

abstract public class Pizza {
	String name;
	String dough;
	String sauce;
	ArrayList<String> toppings = new ArrayList<String>();

	public String getName() {
		return name;
	}

	public void prepare() {
		System.out.println("Preparing " + name);
	}

	public void bake() {
		System.out.println("Baking " + name);
	}

	public void cut() {
		System.out.println("Cutting " + name);
	}

	public void box() {
		System.out.println("Boxing " + name);
	}

	public String toString() {
		// code to display pizza name and ingredients
		StringBuffer display = new StringBuffer();
		display.append("---- " + name + " ----\n");
		display.append(dough + "\n");
		display.append(sauce + "\n");
		for (int i = 0; i < toppings.size(); i++) {
			display.append((String )toppings.get(i) + "\n");
		}
		return display.toString();
	}
}

VeggiePizza.java

package com.javaskool;

public class VeggiePizza extends Pizza {
	public VeggiePizza() {
		name = "Veggie Pizza";
		dough = "Crust";
		sauce = "Marinara sauce";
		toppings.add("Shredded mozzarella");//Mild white Italian cheese
		toppings.add("Grated parmesan");
		toppings.add("Diced onion");
		toppings.add("Sliced mushrooms");
		toppings.add("Sliced red pepper");
		toppings.add("Sliced black olives");
	}
}

CheesePizza.java

package com.javaskool;

public class CheesePizza extends Pizza {
	public CheesePizza() {
		name = "Cheese Pizza";
		dough = "Regular Crust";
		sauce = "Marinara Pizza Sauce";
		toppings.add("Fresh Mozzarella");
		toppings.add("Parmesan");//parmesan=>Hard dry sharp-flavoured Italian cheese
	}
}

PepperoniPizza.java

package com.javaskool;

public class PepperoniPizza extends Pizza {
	public PepperoniPizza() {
		name = "Pepperoni Pizza";
		dough = "Crust";
		sauce = "Marinara sauce";
		toppings.add("Sliced Pepperoni");
		toppings.add("Sliced Onion");
		toppings.add("Grated parmesan cheese");
	}
}

ClamPizza.java

package com.javaskool;

public class ClamPizza extends Pizza {
	public ClamPizza() {
		name = "Clam Pizza";
		dough = "Thin crust";
		sauce = "White garlic sauce";
		toppings.add("Clams");
		toppings.add("Grated parmesan cheese");
	}
}

SimplePizzaFactory.java

package com.javaskool;

public class SimplePizzaFactory {

	public Pizza createPizza(String type) {
		Pizza pizza = null;

		if (type.equals("cheese")) {
			pizza = new CheesePizza();
		} else if (type.equals("pepperoni")) {
			pizza = new PepperoniPizza();
		} else if (type.equals("clam")) {
			pizza = new ClamPizza();
		} else if (type.equals("veggie")) {
			pizza = new VeggiePizza();
		}
		return pizza;
	}
}

PizzaStore.java

package com.javaskool;

public class PizzaStore {
	SimplePizzaFactory factory;
 
	public PizzaStore(SimplePizzaFactory factory) { 
		this.factory = factory;
	}
 
	public Pizza orderPizza(String type) {
		Pizza pizza;
 
		pizza = factory.createPizza(type);
 
		pizza.prepare();
		pizza.bake();
		pizza.cut();
		pizza.box();

		return pizza;
	}

}

PizzaTestDrive.java

package com.javaskool;

public class PizzaTestDrive {
 
	public static void main(String[] args) {
		SimplePizzaFactory factory = new SimplePizzaFactory();
		PizzaStore store = new PizzaStore(factory);

		Pizza pizza = store.orderPizza("cheese");
		System.out.println("We ordered a " + pizza.getName() + "\n");
 
		pizza = store.orderPizza("veggie");
		System.out.println("We ordered a " + pizza.getName() + "\n");
//you can also look for pepperoni and clam pizza.

	}
}

Output

c:\>javac -d . *.java
c:\>java com.javaskool.PizzaTestDrive
Preparing Cheese Pizza
Baking Cheese Pizza
Cutting Cheese Pizza
Boxing Cheese Pizza
We ordered a Cheese Pizza

Preparing Veggie Pizza
Baking Veggie Pizza
Cutting Veggie Pizza
Boxing Veggie Pizza
We ordered a Veggie Pizza

UML Diagram for Pizza Application having Implementation of Factory Design Pattern

Download:

Factory Design Pattern Code (13KB)