創建完美的程式碼：理解創建模式

這是一系列關於設計模式的部落格的開始。在本部落格中，我們將討論第一種設計模式，即創建模式。這裡將透過一些現實世界的例子來討論屬於創建模式的類型。我將使用 Java 作為我的選擇語言。

什麼是設計模式？

設計模式在軟體開發中發揮著至關重要的作用，為常見問題提供經過驗證的解決方案並推廣最佳實踐。它們就像預製的藍圖，您可以自訂它們來解決程式碼中反覆出現的設計問題。

探索 Java 中的創意設計模式

在物件導向程式設計中，創建設計模式發揮著重要作用，因為它們使物件實例化與其使用分離成為可能，從而提高了物件創建的靈活性和可擴展性。這篇部落格文章將重點放在五種主要類型的創建設計模式：工廠方法、抽象工廠、建構器、原型和單例。為了展示每個方法的工作原理，我們將使用 Java 中的實際範例。

1。工廠方法

工廠方法模式定義了一個用於創建物件的接口，但允許子類別更改將創建的物件的類型。此模式支援 Java 中的松耦合，無需將特定於應用程式的類別綁定到程式碼中。

現實場景：假設一家物流公司使用卡車和船舶等各種車輛運輸貨物。車輛類型取決於所需的運輸方式。

// Product Interface
interface Transport {
    void deliver();
}

// Concrete Products
class Truck implements Transport {
    @Override
    public void deliver() {
        System.out.println("Deliver by land in a truck.");
    }
}

class Ship implements Transport {
    @Override
    public void deliver() {
        System.out.println("Deliver by sea in a ship.");
    }
}

// Creator
abstract class Logistics {
    public abstract Transport createTransport();

    public void planDelivery() {
        Transport transport = createTransport();
        transport.deliver();
    }
}

// Concrete Creators
class RoadLogistics extends Logistics {
    @Override
    public Transport createTransport() {
        return new Truck();
    }
}

class SeaLogistics extends Logistics {
    @Override
    public Transport createTransport() {
        return new Ship();
    }
}

// let's call the main class
public class Main {
    public static void main(String[] args) {
        Logistics logistics = new RoadLogistics();
        logistics.planDelivery();

        logistics = new SeaLogistics();
        logistics.planDelivery();
    }
}

2。抽象工廠

抽象工廠模式提供了一個介面，用於建立相關或依賴物件系列，而無需指定它們的特定類別。當系統需要獨立於其物件的創建方式時，它非常有用。

現實生活場景：想像一家家具店，出售不同類型的家具套裝，例如維多利亞風格和現代風格。每套都包含椅子、沙發等產品。

// Abstract Products
interface Chair {
    void sitOn();
}

interface Sofa {
    void lieOn();
}

// Concrete Products
class VictorianChair implements Chair {
    @Override
    public void sitOn() {
        System.out.println("Sitting on a Victorian chair.");
    }
}

class ModernChair implements Chair {
    @Override
    public void sitOn() {
        System.out.println("Sitting on a Modern chair.");
    }
}

class VictorianSofa implements Sofa {
    @Override
    public void lieOn() {
        System.out.println("Lying on a Victorian sofa.");
    }
}

class ModernSofa implements Sofa {
    @Override
    public void lieOn() {
        System.out.println("Lying on a Modern sofa.");
    }
}

// Abstract Factory
interface FurnitureFactory {
    Chair createChair();
    Sofa createSofa();
}

// Concrete Factories
class VictorianFurnitureFactory implements FurnitureFactory {
    @Override
    public Chair createChair() {
        return new VictorianChair();
    }

    @Override
    public Sofa createSofa() {
        return new VictorianSofa();
    }
}

class ModernFurnitureFactory implements FurnitureFactory {
    @Override
    public Chair createChair() {
        return new ModernChair();
    }

    @Override
    public Sofa createSofa() {
        return new ModernSofa();
    }
}

// Client code
public class Main {
    private static void createFurniture(FurnitureFactory factory) {
        Chair chair = factory.createChair();
        Sofa sofa = factory.createSofa();
        chair.sitOn();
        sofa.lieOn();
    }

    public static void main(String[] args) {
        FurnitureFactory victorianFactory = new VictorianFurnitureFactory();
        createFurniture(victorianFactory);

        FurnitureFactory modernFactory = new ModernFurnitureFactory();
        createFurniture(modernFactory);
    }
}

3。建造者

Builder 模式將複雜物件的建構與其表示分離，允許相同的建構過程建立不同的表示。它對於創建具有許多可選屬性的物件特別有用。

現實場景：考慮一個線上披薩訂購系統，客戶可以使用各種配料、尺寸和外皮類型客製化披薩。

// Product
class Pizza {
    private String dough = "";
    private String sauce = "";
    private String topping = "";

    public void setDough(String dough) { this.dough = dough; }
    public void setSauce(String sauce) { this.sauce = sauce; }
    public void setTopping(String topping) { this.topping = topping; }

    @Override
    public String toString() {
        return "Pizza [dough=" + dough + ", sauce=" + sauce + ", topping=" + topping + "]";
    }
}

// Builder Interface
interface PizzaBuilder {
    void buildDough();
    void buildSauce();
    void buildTopping();
    Pizza getPizza();
}

// Concrete Builders
class HawaiianPizzaBuilder implements PizzaBuilder {
    private Pizza pizza;

    public HawaiianPizzaBuilder() {
        this.pizza = new Pizza();
    }

    @Override
    public void buildDough() { pizza.setDough("cross"); }
    @Override
    public void buildSauce() { pizza.setSauce("mild"); }
    @Override
    public void buildTopping() { pizza.setTopping("ham+pineapple"); }
    @Override
    public Pizza getPizza() { return this.pizza; }
}

class SpicyPizzaBuilder implements PizzaBuilder {
    private Pizza pizza;

    public SpicyPizzaBuilder() {
        this.pizza = new Pizza();
    }

    @Override
    public void buildDough() { pizza.setDough("pan baked"); }
    @Override
    public void buildSauce() { pizza.setSauce("hot"); }
    @Override
    public void buildTopping() { pizza.setTopping("pepperoni+salami"); }
    @Override
    public Pizza getPizza() { return this.pizza; }
}

// Director
class Waiter {
    private PizzaBuilder pizzaBuilder;

    public void setPizzaBuilder(PizzaBuilder pb) { pizzaBuilder = pb; }
    public Pizza getPizza() { return pizzaBuilder.getPizza(); }

    public void constructPizza() {
        pizzaBuilder.buildDough();
        pizzaBuilder.buildSauce();
        pizzaBuilder.buildTopping();
    }
}

// Client code
public class Main {
    public static void main(String[] args) {
        Waiter waiter = new Waiter();
        PizzaBuilder hawaiianPizzaBuilder = new HawaiianPizzaBuilder();
        PizzaBuilder spicyPizzaBuilder = new SpicyPizzaBuilder();

        waiter.setPizzaBuilder(hawaiianPizzaBuilder);
        waiter.constructPizza();
        Pizza pizza1 = waiter.getPizza();
        System.out.println("Pizza built: " + pizza1);

        waiter.setPizzaBuilder(spicyPizzaBuilder);
        waiter.constructPizza();
        Pizza pizza2 = waiter.getPizza();
        System.out.println("Pizza built: " + pizza2);
    }
}

4。原型

原型模式用於透過複製現有物件（稱為原型）來建立新物件。當建立新物件的成本昂貴時，此模式很有用。

現實場景：想像一個圖形編輯器，您可以在其中建立、複製和編輯形狀。

import java.util.HashMap;
import java.util.Map;

// Prototype
abstract class Shape implements Cloneable {
    private String id;
    protected String type;

    abstract void draw();

    public String getType() { return type; }
    public String getId() { return id; }
    public void setId(String id) { this.id = id; }

    public Object clone() {
        Object clone = null;
        try {
            clone = super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return clone;
    }
}

// Concrete Prototypes
class Rectangle extends Shape {
    public Rectangle() { type = "Rectangle"; }
    @Override
    public void draw() { System.out.println("Drawing a Rectangle."); }
}

class Circle extends Shape {
    public Circle() { type = "Circle"; }
    @Override
    public void draw() { System.out.println("Drawing a Circle."); }
}

// Prototype Registry
class ShapeCache {
    private static Map<String, Shape> shapeMap = new HashMap<>();

    public static Shape getShape(String shapeId) {
        Shape cachedShape = shapeMap.get(shapeId);
        return (Shape) cachedShape.clone();
    }

    public static void loadCache() {
        Rectangle rectangle = new Rectangle();
        rectangle.setId("1");
        shapeMap.put(rectangle.getId(), rectangle);

        Circle circle = new Circle();
        circle.setId("2");
        shapeMap.put(circle.getId(), circle);
    }
}

// Client code
public class Main {
    public static void main(String[] args) {
        ShapeCache.loadCache();

        Shape clonedShape1 = ShapeCache.getShape("1");
        System.out.println("Shape: " + clonedShape1.getType());

        Shape clonedShape2 = ShapeCache.getShape("2");
        System.out.println("Shape: " + clonedShape2.getType());
    }
}

5。辛格頓

單例模式確保一個類別只有一個實例並提供對其的全域存取點。此模式通常用於日誌記錄、快取和執行緒池。

現實場景：想像一個印表機後台處理程序，其中只有一個實例應該管理所有列印作業。

class PrinterSpooler {
    private static PrinterSpooler instance;

    private PrinterSpooler() {
        // private constructor to prevent instantiation
    }

    public static PrinterSpooler getInstance() {
        if (instance == null) {
            instance = new PrinterSpooler();
        }
        return instance;
    }

    public void print(String document) {
        System.out.println("Printing document: " + document);
    }
}

// Client code
public class Main {
    public static void main(String[] args) {
        PrinterSpooler spooler1 = PrinterSpooler.getInstance();
        PrinterSpooler spooler2 = PrinterSpooler.getInstance();

        spooler1.print("Document 1");
        spooler2.print("Document 2");

        System.out.println("Are both spoolers the same instance? " + (spooler1 == spooler2));
    }
}

參考

https://refactoring.guru/

https://www.javatpoint.com/design-patterns-in-java

https://www.digitalocean.com/community/tutorials/java-design-patterns-example-tutorial

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