良いコード／悪いコードで学ぶ設計入門を読んで書いたコード

thinkingAbout_6_3.java

import java.util.HashMap;
import java.util.Map;
import java.util.HashSet;
import java.util.Set;

class Main {
    public static void main(String[] args) {
        final Customer customerA = new Customer("ID-0001");
        final Customer customerB = new Customer("ID-0002");
        final Customer customerC = new Customer("ID-0003");

        System.out.println(customerA.name() + " : " + customerA.stageRank());
        System.out.println(customerB.name() + " : " + customerB.stageRank());
        System.out.println(customerC.name() + " : " + customerC.stageRank());
    }
}

/**
 * Customerクラスを定義
 * こうすることでより見通しが良くなる気がする。
 */
class Customer {
    private final String id;
    private final String name;
    private final PurchaseHistory history;
    private final GoldCustomerPolicy goldCustomerPolicy = new GoldCustomerPolicy();
    private final SilverCustomerPolicy silverCustomerPolicy = new SilverCustomerPolicy();

    Customer(final String id) {
        this.id = id;
        final CustomerDate customerDate = new CustomerDate();
        final CustomerDetail customerDetail = customerDate.getCustomerDetail(id);
        this.name = customerDetail.name();
        this.history = customerDetail.history();
    }

    String stageRank() {
        if (goldCustomerPolicy.complyWithAll(history)) return "Gold";
        if (silverCustomerPolicy.complyWithAll(history)) return "Silver";
        return "Normal";
    }

    String name() {
        return this.name;
    }
}

class CustomerDate {
    final Map<String, CustomerDetail> customers = new HashMap<>();
    CustomerDate() {
        customers.put("ID-0001", new CustomerDetail("アリス", new PurchaseHistory(2000000, 24, 0.0001f)));
        customers.put("ID-0002", new CustomerDetail("ボブ", new PurchaseHistory(20000, 12, 0.0f)));
        customers.put("ID-0003", new CustomerDetail("チャーリー", new PurchaseHistory(300000, 15, 0.003f)));
    }

    CustomerDetail getCustomerDetail(final String id) {
        return customers.get(id);
    }
}

class CustomerDetail {
    private final String name;
    private final PurchaseHistory history;

    CustomerDetail(final String name, final PurchaseHistory history) {
        this.name = name;
        this.history = history;
    }

    String name() {
        return this.name;
    }

    PurchaseHistory history() {
        return this.history;
    }
}

class PurchaseHistory {
    final int totalAmount;
    final int purchaseFrequencyPerMonth;
    final float returnRate;

    PurchaseHistory(final int totalAmount, final int purchaseFrequencyPerMonth, final float returnRate){
        this.totalAmount = totalAmount;
        this.purchaseFrequencyPerMonth = purchaseFrequencyPerMonth;
        this.returnRate = returnRate;
    }
}

/**
 * ECサイトにおいて優良顧客かどうかを判定するロジックを
 * if switch はなるべく使わないように、Interfaceを用いて実装する。
 */

interface ExcellentCustomerRule {
    boolean ok(final PurchaseHistory history);
}

class GoldCustomerPurchaseAmountRule implements ExcellentCustomerRule {
    public boolean ok(final PurchaseHistory history) {
        return 100000 <= history.totalAmount;
    }
}

class PurchaseFrequencyRule implements ExcellentCustomerRule {
    public boolean ok(final PurchaseHistory history) {
        return 10 <= history.purchaseFrequencyPerMonth;
    }
}

class ReturnRateRule implements ExcellentCustomerRule {
    public boolean ok(final PurchaseHistory history) {
        return history.returnRate <= 0.001;
    }
}

class ExcellentCustomerPolicy {
    private final Set<ExcellentCustomerRule> rules;

    ExcellentCustomerPolicy() {
        rules = new HashSet();
    }

    void add(final ExcellentCustomerRule rule) {
        rules.add(rule);
    }

    boolean complyWithAll(final PurchaseHistory history) {
        for (ExcellentCustomerRule each : rules) {
            if (!each.ok(history)) return false;
        }
        return true;
    }
}

class GoldCustomerPolicy {
    private final ExcellentCustomerPolicy policy;

    GoldCustomerPolicy() {
        policy = new ExcellentCustomerPolicy();
        policy.add(new GoldCustomerPurchaseAmountRule());
        policy.add(new PurchaseFrequencyRule());
        policy.add(new ReturnRateRule());
    }

    boolean complyWithAll(final PurchaseHistory history) {
        return policy.complyWithAll(history);
    }
}

class SilverCustomerPolicy {
    private final ExcellentCustomerPolicy policy;

    SilverCustomerPolicy() {
        policy = new ExcellentCustomerPolicy();
        policy.add(new PurchaseFrequencyRule());
        policy.add(new ReturnRateRule());
    }

    boolean complyWithAll(final PurchaseHistory history) {
        return policy.complyWithAll(history);
    }
}