Introduction to Builder Pattern and Prototype Pattern in Java Design Patterns (Code Example)

This article brings you an introduction to the builder pattern and prototype pattern in Java design patterns (code examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you. help.

Preface

In the previous article we learned about the factory pattern and introduced the simple factory pattern, factory method and abstract factory pattern. This article introduces the builder pattern and prototype pattern, which are creative patterns in design patterns.

Builder Pattern

Introduction

The builder pattern is a creational pattern. The builder pattern uses multiple simple objects to build a complex object step by step. This type of design pattern is a creational pattern, which provides an optimal way to create objects.
To put it simply, it is to extract a complex thing and provide a simple call to the outside world, which can create different representations in the same construction process. It is very similar to the factory mode, but it pays more attention to the assembly of components.

Here is an example to illustrate.
The food we eat every day includes pancakes, lunch boxes, ramen, soy milk, milk and juice. It is divided into three meals, breakfast, lunch and dinner. The meals mainly include food (commonly known as rice) and drink (soy milk, juice, etc.), then we can have pancakes and soy milk as breakfast, and box lunch and juice as lunch, so We can know exactly what to eat for breakfast and lunch.

First we define a food category with two attributes, food and drink.

class Meal{
    private String food;
    private String drinks;
    
    public String getFood() {
        return food;
    }
    public void setFood(String food) {
        this.food = food;
    }
    
    public String getDrinks() {
        return drinks;
    }
    public void setDrinks(String drinks) {
        this.drinks = drinks;
    }
}

When we define food, we are defining a standard interface for food. What does a piece of food contain? In fact, it means eating and drinking.

interface IBuilderFood{
    void buildFood();
    void buildDrinks();
    Meal createMeal();
}

The food interface defines an eating and a drinking component, and then returns the food we need through the createMeal() method.
So now we can define a breakfast and lunch.
Code example:

class Breakfast implements IBuilderFood{
    Meal meal;

    public Breakfast(){
        meal=new Meal();
    }
    
    @Override
    public void buildFood() {
        meal.setFood("煎饼");
    }

    @Override
    public void buildDrinks() {
        meal.setDrinks("豆浆");   
    }
    
    @Override
    public Meal createMeal() {
        return meal;
    }
}

class Lunch implements IBuilderFood{
    Meal meal;

    public Lunch(){
        meal=new Meal();
    }
    
    @Override
    public void buildFood() {
        meal.setFood("盒饭");
    }

    @Override
    public void buildDrinks() {
        meal.setDrinks("果汁");   
    }
    
    @Override
    public Meal createMeal() {
        return meal;
    }
}

After the definition, the process of creating breakfast and lunch is complete. But this is not the builder mode. It has a core Director, which is used to create parts of complex objects, create the parts completely or create them according to certain rules. So here we can create a Director to create a meal. As for what meal is created, it does not need to know, this is decided by the caller.

Here we can define a restaurant and create a meal. The customer decides what meal to create.
Code example:

class FoodStore{
    public Meal createBreakfast(IBuilderFood bf){
        bf.buildDrinks();
        bf.buildFood();
        return bf.createMeal();
    }
}

After creating this Director, we will call the test again.

Code example:

public class BuilderTest {

    public static void main(String[] args) {
        FoodStore foodStore=new FoodStore();
        Meal meal=foodStore.createBreakfast(new Breakfast());
        Meal meal2=foodStore.createBreakfast(new Lunch());
        System.out.println("小明早上吃的是:"+meal.getFood()+",喝的饮料是:"+meal.getDrinks());
        System.out.println("小明中午吃的是:"+meal2.getFood()+",喝的饮料是:"+meal2.getDrinks()); 
    }

}

Output result:

小明早上吃的是:煎饼,喝的饮料是:豆浆
小明中午吃的是:盒饭,喝的饮料是:果汁

Briefly introduces the operating principle of the builder mode. It can be summarized as these 4 points:

1. Builder: Specifies an abstract interface, stipulates the creation of the required implementation components for the product, and does not involve the creation of specific object components.

2. ConcreteBuilder: It is necessary to implement the Builder interface, and create different methods for different logics, and finally provide an instance of the product.

3. Director: Used to create the part of complex objects. Create this part completely or according to certain rules.

4. Product: Indicates the constructed complex object.

Usage scenarios:
Applicable when some basic components are inconvenient, but the combination changes frequently. For example, a supermarket promotion gift package.

Advantages:

1. The builder is independent and easy to expand.

2. Easy to control detailed risks.

Disadvantages

1. The internal structure is complex and difficult to understand.

2. The products directly need to have something in common and the scope should be controlled.

Prototype Pattern

The Prototype Pattern (Prototype Pattern) is used to create repeated objects while ensuring performance. This type of design pattern is a creational pattern, which provides an optimal way to create objects.

Generally speaking, when we create an object, we create it directly. However, when the cost of creating the object is high, repeated creation is not cost-effective. In this case, we can use the prototype mode.
For example, we have all sent emails. During festivals, we usually send blessings. Most of these blessings are the same except for the names. At this time we can use this mode to create accordingly.

Here is a simple example to illustrate.
Xiao Ming and Xiao Hong have their birthdays on the same day, so we need to send them emails to wish them well, but because we are lazy, the blessing words are the same except for their names. At this time, we can first complete the writing of the blessing, then clone the blessing, and finally send it according to different names. But I’ll keep it simple here, just print it out.

Code example:

public class PrototypeTest {

    public static void main(String[] args) {
        Mail mail=new Mail();
        mail.setMsg("生日快乐!");
        Mail mail2=(Mail) mail.clone();
        mail.setName("小明");
        mail2.setName("小红");
        System.out.println(mail.toString());
        System.out.println(mail2.toString());
    }
}

 class Mail implements Cloneable {
    private String name;
    private String msg;
    
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
    public Object clone() {
        Object clone = null;
        try {
            clone = super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return clone;
    }

    @Override
    public String toString() {
        return name + ":" + msg ;
    }
    
}

Output result:

小明:生日快乐!
小红:生日快乐!

看完原型模式的创建，是不是感觉就是和Java中克隆即为类似呢?
实际上它的核心也就是克隆。
克隆有两种，浅克隆和深克隆，本文主要介绍的是浅克隆。
浅克隆:

在浅克隆中，如果原型对象的成员变量是值类型，将复制一份给克隆对象；如果原型对象的成员变量是引用类型，则将引用对象的地址复制一份给克隆对象，也就是说原型对象和克隆对象的成员变量指向相同的内存地址。
简单来说，在浅克隆中，当对象被复制时只复制它本身和其中包含的值类型的成员变量，而引用类型的成员对象并没有复制。
实现Cloneable接口并重写Object类中的clone()方法；

深克隆:

在深克隆中，无论原型对象的成员变量是值类型还是引用类型，都将复制一份给克隆对象，深克隆将原型对象的所有引用对象也复制一份给克隆对象。

简单来说，在深克隆中，除了对象本身被复制外，对象所包含的所有成员变量也将复制。
实现Serializable接口，通过对象的序列化和反序列化实现克隆，可以实现真正的深度克隆。

使用场景:

1. 类初始化的时候需要消耗大量资源的时候；

2. 获取数据库连接繁琐的时候；

3. 一个对象，有很多个修改者的时候；

优点:
1.可以提升性能；

缺点:
1.因为必须实现Cloneable 接口，所以用起来可能不太方便。

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Java设计模式中工厂模式的介绍（代码示例）

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