Design Patterns - Builder
// Design Patterns - The Builder Pattern:
Builder patterns builds a complex object using simple objects.
// Step 1: Create the Item interface representing food item
// and the Packing interface.
public interface Item {
public String name();
public Packing packing();
public float price();
}
public interface Packing {
public String pack();
}
// Step 2: Create concrete classes implementing the Packing interface.
public class Wrapper implements Packing {
public String pack() {
return "Wrapper";
}
}
public class Bottle implements Packing {
public String pack() {
return "Bottle";
}
}
// Step 3: Create abstract classes implementing the Item interface providing
// default functionalities.
public abstract class Burger implements Item {
public Packing packing() {
return new Wrapper();
}
public abstract float price();
}
public abstract class ColdDrink implements Item {
public Packing packing() {
return new Bottle();
}
public abstract float price();
}
// Step 4: Create concrete classes extending Burger and ColdDrink classes
public class VegBurger extends Burger {
public float price() {
return 25.0f;
}
public String name() {
return "Veg Burger";
}
}
public class ChickenBurger extends Burger {
public float price() {
return 50.5f;
}
public String name() {
return "Chicken Burger";
}
}
public class Coke extends ColdDrink {
public float price() {
return 30.0f;
}
public String name() {
return "Coke";
}
}
public class Pepsi extends ColdDrink {
public float price() {
return 35.0f;
}
public String name() {
return "Pepsi";
}
}
// Step 5: Create a Meal class having Item objects defined above.
public class Meal {
private List<Item> items = new ArrayList<Item>();
public void addItem(Item item){
items.add(item);
}
public float getCost(){
float cost = 0.0f;
for (Item item : items) {
cost += item.price();
}
return cost;
}
public void showItems(){
for (Item item : items) {
System.out.print("Item : " + item.name());
System.out.print(", Packing : " + item.packing().pack());
System.out.println(", Price : " + item.price());
}
}
}
// Step 6: Create a MealBuilder class, the actual builder class responsible to
// create Meal objects.
public class MealBuilder {
public Meal prepareVegMeal (){
Meal meal = new Meal();
meal.addItem(new VegBurger());
meal.addItem(new Coke());
return meal;
}
public Meal prepareNonVegMeal (){
Meal meal = new Meal();
meal.addItem(new ChickenBurger());
meal.addItem(new Pepsi());
return meal;
}
}
// Use the builder class
MealBuilder mealBuilder = new MealBuilder();
Meal vegMeal = mealBuilder.prepareVegMeal();
System.out.println("Veg Meal");
vegMeal.showItems();
System.out.println("Total Cost: " + vegMeal.getCost());
Meal nonVegMeal = mealBuilder.prepareNonVegMeal();
System.out.println("\n\nNon-Veg Meal");
nonVegMeal.showItems();
System.out.println("Total Cost: " + nonVegMeal.getCost());
public class ItemBuilder {
private Item item = new Item();
public ItemBuilder id(int id) {
item.setId(id);
return this;
}
public ItemBuilder description(String description) {
item.setDescription(description);
return this;
}
public ItemBuilder checked() {
item.setChecked(true);
return this;
}
public Item build() {
return item;
}
}
// Now we can start writing things like this:
Item myItem = new ItemBuilder().id(1).checked().description("My first item").build();
page revision: 4, last edited: 11 Nov 2017 15:25