행동 매개변수화

import java.util.ArrayList;
import java.util.List;

public final class DuplicatedProductFilters {
    record Product(String name, int price, int stock) {
    }

    static List<Product> expensive(List<Product> products, int minimum) {
        List<Product> result = new ArrayList<>();
        for (Product product : products) {
            if (product.price() >= minimum) {
                result.add(product);
            }
        }
        return result;
    }

    static List<Product> available(List<Product> products) {
        List<Product> result = new ArrayList<>();
        for (Product product : products) {
            if (product.stock() > 0) {
                result.add(product);
            }
        }
        return result;
    }

    public static void main(String[] args) {
        System.out.println("compile-only duplicated loop counterexample");
    }
}

import java.util.ArrayList;
import java.util.List;

public final class BehaviorParameterization {
    record Product(String name, String category, int price, int stock) {
    }

    @FunctionalInterface
    interface ProductRule {
        boolean test(Product product);

        default ProductRule and(ProductRule other) {
            return product -> test(product) && other.test(product);
        }

        default ProductRule negate() {
            return product -> !test(product);
        }
    }

    static List<Product> select(List<Product> products, ProductRule rule) {
        List<Product> selected = new ArrayList<>();
        for (Product product : products) {
            if (rule.test(product)) {
                selected.add(product);
            }
        }
        return List.copyOf(selected);
    }

    static final class CategoryRule implements ProductRule {
        private final String category;

        CategoryRule(String category) {
            this.category = category;
        }

        @Override
        public boolean test(Product product) {
            return product.category().equals(category);
        }
    }

    public static void main(String[] args) {
        List<Product> products = List.of(
                new Product("Keyboard", "device", 120, 3),
                new Product("Cable", "device", 15, 0),
                new Product("Book", "book", 35, 8));
        ProductRule device = new CategoryRule("device");
        ProductRule available = product -> product.stock() > 0;
        ProductRule affordable = product -> product.price() <= 100;

        System.out.println(select(products, device.and(available)));
        System.out.println(select(products, available.and(affordable)));
        System.out.println(select(products, available.negate()));
    }
}

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public final class ComparatorPolicy {
    record Ticket(String id, int severity, long openedAt) {
    }

    static List<Ticket> orderedCopy(List<Ticket> tickets, Comparator<Ticket> order) {
        List<Ticket> copy = new ArrayList<>(tickets);
        copy.sort(order);
        return List.copyOf(copy);
    }

    public static void main(String[] args) {
        List<Ticket> tickets = List.of(
                new Ticket("T-3", 2, 300),
                new Ticket("T-1", 1, 200),
                new Ticket("T-2", 1, 100));
        Comparator<Ticket> queueOrder = Comparator
                .comparingInt(Ticket::severity)
                .thenComparingLong(Ticket::openedAt)
                .thenComparing(Ticket::id);
        Comparator<Ticket> newestFirst = Comparator
                .comparingLong(Ticket::openedAt)
                .reversed();

        System.out.println(orderedCopy(tickets, queueOrder));
        System.out.println(orderedCopy(tickets, newestFirst));
        System.out.println("original=" + tickets);
    }
}