生成器模式

📢 本文由 gemini-3-flash-preview 翻譯

Builder Pattern 物件建立型模式

意圖

將一個複雜物件的建構與它的表示分離，使得同樣的建構過程可以建立不同的表示。

結構

其中：

Builder 為建立一個 Product 物件的各個部件指定抽象介面。
ConcreteBuilder 實作 Builder 的介面以建構和裝配該產品的各個部件，定義並明確它所建立的表示，提供一個取得產品的介面。
Director 建構一個使用 Builder 介面的物件。
Product 表示被建構的複雜物件。ConcreteBuilder 建立該產品的內部表示並定義它的裝配過程。包含定義組成元件的類別，包括將這些元件裝配成最終產品的介面。

適用性

Builder 模式適用於：

當建立複雜物件的演算法應該獨立於該物件的組成部分以及它們的裝配方式。
當建構過程必須允許被建構的物件有不同的表示時。

範例 1

某速食店主要製作並出售兒童套餐，一般包括主餐（各類披薩）、飲料和玩具，其餐點種類可能不同，但其製作過程相同。前台服務員（Waiter）排程廚師製作套餐。現採用生成器模式實作製作過程。類別圖如下：

生成器模式-範例

Java

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class Pizza {
    private String parts;
    public void setParts(String parts) { this.parts = parts; }
    public String toString() { return this.parts; }
}

abstract class PizzaBuilder {
    protected Pizza pizza;
    public Pizza getPizza() { return pizza; }
    public void createNewPizza() { pizza = new Pizza(); }
    public abstract void buildParts();
}

class HawaiianPizzaBuilder extends PizzaBuilder {
    public void buildParts(){
        pizza.setParts("cross + mild + ham&pineapp1e");
    }
}

class SpicyPizzaBuilder extends PizzaBuilder {
    public void buildParts() {
        pizza.setParts("panbaked + hot + pepperoni&salami");
    }
}

class Waiter {
    private PizzaBuilder pizzaBuilder;
    public void setPizzaBuilder(PizzaBuilder pizzaBuilder) {/* 設定生成器 */
        this.pizzaBuilder = pizzaBuilder;
    }
    public Pizza getPizza() { return pizzaBuilder.getPizza(); }
    public void construct() { /* 建構 */
        pizzaBuilder.createNewPizza();
        pizzaBuilder.buildParts();
    }
}
class FastFoodOrdering {
    public static void main(String[] args) {
        Waiter waiter = new Waiter();
        PizzaBuilder hawaiian_pizzabuilder = new HawaiianPizzaBuilder();
        waiter.setPizzaBuilder(hawaiian_pizzabuilder);
        waiter.construct();
        System.out.println("披薩：" + waiter.getPizza());
        // 輸出：披薩：cross + mild + ham&pineapp1e
    }
}

C++

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#include <iostream>
#include <string>
using namespace std;

class Pizza
{
private:
    string parts;

public:
    void setParts(string parts) { this->parts = parts; }
    string getParts() { return parts; }
};

class PizzaBuilder
{
protected:
    Pizza *pizza;

public:
    Pizza *getPizza() { return pizza; }
    void createNewPizza() { pizza = new Pizza(); }
    virtual void buildParts() = 0;
};

class HawaiianPizzaBuilder : public PizzaBuilder
{
public:
    void buildParts() { pizza->setParts("cross + mild + ham&pineapple"); }
};

class SpicyPizzaBuilder : public PizzaBuilder
{
public:
    void buildParts()
    {
        pizza->setParts("pan baked + hot + pepperoni&salami");
    }
};

class Waiter
{
private:
    PizzaBuilder *pizzaBuilder;

public:
    void setPizzaBuilder(PizzaBuilder *pizzaBuilder)
    { /* 設定生成器 */
        this->pizzaBuilder = pizzaBuilder;
    }
    Pizza *getPizza() { return pizzaBuilder->getPizza(); }
    void construct()
    {
        pizzaBuilder->createNewPizza();
        pizzaBuilder->buildParts();
    }
};

int main()
{
    Waiter *waiter = new Waiter();
    PizzaBuilder *hawaiian_pizzabuilder = new HawaiianPizzaBuilder();
    waiter->setPizzaBuilder(hawaiian_pizzabuilder);
    waiter->construct();
    cout << "pizza: " << waiter->getPizza()->getParts() << endl;
}

// 程式的輸出結果為：
// pizza：cross + mild + ham*pineapple

範例 2

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import java.util.*;

public class Main{
    public static void main(String[] args) {
        Director d = new Director();
        Builder b1 = new Builder1();

        d.Construct(b1);
        Product p1 = b1.getResult();
        p1.show();
    }
}

class Product{
    List<String> parts = new ArrayList<String>();
    
    public void Add(String part){
        parts.add(part);
    }
    
    public void show(){
        System.out.println("產品資訊：");
        for(String s : parts)
            System.out.print(s + " ");
        System.out.println();
    }
}

abstract class Builder{
    public abstract void BuildPart();
    public abstract Product getResult();
}

class Builder1 extends Builder{
    Product p = new Product();

    @Override
    public void BuildPart(){
        p.Add("A1");
        p.Add("A2");
        p.Add("C");
    }

    @Override
    public Product getResult(){
        return p;
    }
}

class Builder2 extends Builder{
    Product p = new Product();

    @Override
    public void BuildPart(){
        p.Add("B1");
        p.Add("B2");
        p.Add("C");
    }

    @Override
    public Product getResult(){
        return p;
    }
}

class Director{
    public void Construct(Builder builder){
        builder.BuildPart();
    }
}