This is the seventh day of my participation in the August More text Challenge. For details, see:August is more challenging

The Builder Pattern uses multiple simple objects to build a complex object step by step. This type of design pattern is a creation pattern that provides an optimal way to create objects. A Builder class constructs the final object step by step. The Builder class is independent of other objects.


describe parsing
intentions Separating a complex build from its representation allows the same build process to create different representations.
Mainly to solve The main solution is in the software system, sometimes faced with the creation of “a complex object”, which is usually composed of various parts of the sub-objects with a certain algorithm; As demand changes,
When to use Some of the basic components do not change, and their composition often changes.
How to solve Separate change from invariance.
The key code The builders
Examples of application 1, go to KFC, hamburgers, coke, French fries, fried chicken wings and so on are unchanged, and its combination is often changed, resulting in the so-called “set meal”. 2. JAVA StringBuilder.
advantages 1, the builder is independent, easy to expand. 2, easy to control the details of risk.
disadvantages 1. Products must have something in common and have a limited scope. 2, if the internal changes are complex, there will be many build classes.
Usage scenarios 1. Objects that need to be generated have complex internal structures. 2. The internal properties of the objects that need to be generated depend on each other.
Matters needing attention The difference from the factory pattern is that the builder pattern is more concerned with the order in which parts are assembled.


Consider the business case of a fast food restaurant, where a typical meal could be a Burger and a Cold drink. A Burger, “Burger,” can be a Veg Burger or a Chicken Burger, and they come in a carton. Cold drinks can be Coke (COKE) or Pepsi (Pepsi) and they come in bottles.

  1. We will create one that represents food items such as hamburgers and cold drinksItemInterface and ImplementationItemInterface entity class, and a representation of food packagingPackingInterface and ImplementationPackingIn the physical class of interfaces, burgers come in cartons and cold drinks come in bottles.
  2. And then we create oneMealClass,ItemArrayListAnd one through combinationItemTo create different types ofMealThe object’sMealBuilder.BuilderPatternDemoClass USESMealBuilderTo create aMeal.

Step 1- Create an interface

Create an interface that represents food items and food packaging.

public interface Item {
   public String name();
   public Packing packing();
   public float price();    
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public interface Packing {
   public String pack();
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Step 2- Implement the wrapper interface

Create an entity class that implements the Packing interface.

// Wrapper public class Wrapper implements Packing { @Override public String pack() { return "Wrapper"; }}Copy the code
// public class Bottle implements Packing { @Override public String pack() { return "Bottle"; }}Copy the code

Step 3- Create abstract classes that implement Item: Hamburger and cold drink

Create an abstract class that implements the Item interface and provides the default functionality.

// public abstract class Burger implements Item { @Override public Packing packing() { return new Wrapper();  } @Override public abstract float price(); }Copy the code
public abstract class ColdDrink implements Item {
    public Packing packing() {
       return new Bottle();
    public abstract float price();
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Step 4- Create entity class

Create an entity class that extends Burger and ColdDrink.

// VegBurger. Java public class VegBurger extends Burger {@override public float price() {return 25.0f; } @Override public String name() { return "Veg Burger"; }}Copy the code
Java public class ChickenBurger extends Burger {@override public float price() {return 50.5f; } @Override public String name() { return "Chicken Burger"; }}Copy the code
// public class Coke extends ColdDrink {@override public float price() {return 30.0f; } @Override public String name() { return "Coke"; }}Copy the code
// public class Pepsi extends ColdDrink {@override public float price() {return 35.0f; } @Override public String name() { return "Pepsi"; }}Copy the code

Step 5- Create the package class

Create a Meal class with the Item object defined above.

// import java.util.ArrayList; import java.util.List; 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 : "; System.out.print(", Packing : "+item.packing().pack()); System.out.println(", Price : "+item.price()); }}}Copy the code

Step 6- Set the scenario class

Create a MealBuilder class. The actual Builder class is responsible for creating the Meal object.

// 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; }}Copy the code

Step 7- Call the scenario class

BuiderPatternDemo uses MealBuilder to demonstrate Builder patterns.

// public class BuilderPatternDemo { public static void main(String[] args) { 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()); }}Copy the code

Step 8- Output

Execute the program and print the result:

Veg Meal Item: Veg Burger, Packing: Wrapper, Price: 25.0 Item: Coke, Packing: Bottle, Price: 30.0 55.0 Non-veg Meal Item: Chicken Burger, Packing: Wrapper, Price: 50.5 Item: Pepsi, Packing: Bottle, Price: 35.0 the Total Cost: 85.5Copy the code