策略模式

定義

通用類圖

通用類圖.png

說明：Strategy是算法接口，ConcreteStrategy是算法的具體實(shí)現(xiàn)，Context作用就是將算法封裝起來。

通用代碼

// 策略
public interface Strategy {
    public void doSomething();
}

// 具體策略
public class ConcreteStrategy implements Strategy {
    @Override
    public void doSomething() {
        // 具體算法
    }
}

// 算法封裝
public class Context {
    private Strategy strategy;

    public Context(Strategy strategy) {
        this.strategy = strategy;
    }

    public void doSomething() {
        strategy.doSomething();
    }
}

// 客戶端調(diào)用
public class Client {

    public static void main(String[] args) {
        Strategy strategy = new ConcreteStrategy();
        Context context = new Context(strategy);
        context.doSomething();
    }
}

樣例展示

在圖書銷售時，根據(jù)不同類型的圖書有不同的折扣，計(jì)算金額時必須區(qū)別對待，例如計(jì)算機(jī)類圖書7折，英語類圖書6折。

分析：這里的策略是打折，具體打折策略是計(jì)算機(jī)7折，英語6折，然后將這些打折策略封裝起來給客戶端調(diào)用。

樣例類圖

樣例類圖.png

樣例代碼

// 策略接口
public interface Discount {
    public float discount(float price);
}

// 計(jì)算機(jī)打7折
public class ComputerDiscount implements Discount {
    @Override
    public float discount(float price) {
        return (float) (price * 0.7);
    }
}

// 英語打6折
public class EnglishDiscount implements Discount {
    @Override
    public float discount(float price) {
        return (float) (price * 0.6);
    }
}

// 封裝算法
public class Context {

    private Discount discount;

    public Context(Discount discount) {
        this.discount = discount;
    }

    public float sale(float price) {
        return discount.discount(price);
    }
}

// 客戶端調(diào)用
public class Client {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        float price = scanner.nextFloat();
        String classification = new Scanner(System.in).next();
        Context context = null;
        if ("計(jì)算機(jī)".equals(classification)) {
            context = new Context(new ComputerDiscount());
        } else if ("英語".equals(classification)) {
            context = new Context(new EnglishDiscount());
        }

        System.out.println(context.sale(price));
    }
}

當(dāng)然，這里可以巧用枚舉完成相同的功能

public enum Discount {
    COMPUTER_DISCOUNT() {
        @Override
        public float discount(float price) {
            return (float) (price * 0.7);
        }
    },
    ENGLISH_DISCOUNT() {
        @Override
        public float discount(float price) {
            return (float) (price * 0.6);
        }
    };

    public abstract float discount(float price);
}

// 客戶端調(diào)用
 public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        float price = scanner.nextFloat();
        String classification = new Scanner(System.in).next();
        if ("計(jì)算機(jī)".equals(classification)) {
            System.out.println(Discount.COMPUTER_DISCOUNT.discount(price));
        } else if ("英語".equals(classification)) {
            System.out.println(Discount.ENGLISH_DISCOUNT.discount(price));
        }
    }

本文為《設(shè)計(jì)模式之禪》讀后筆記總結(jié)