Book/모던자바인액션/ 9장. 리팩토링, 테스팅, 디버깅

//람다 표현식
Map<CaloricLevel, List<Dish>> dishesByCaloricLevel = menu.stream()
                        .collect(groupingBy(dish -> {
                                    if (dish.getCalories() <= 400) return CaloricLevel.DIET;
                                    else if (dish.getCalories() <= 700) return CaloricLevel.NORMAL;
                                    else return CaloricLevel.FAT;
}));
//메서드 참조
Map<CaloricLevel, List<Dish>> dishesByCaloricLevel = menu.stream()
                        .collect(groupingBy(Dish::getCaloricLevel));

//스트림을 사용하지 않은 코드
List<String> dishNames = new ArrayList<>();
for(Dish dish: menu) {
    if(dish.getCalories() > 300) {
        dishNames.add(dish.getName());
    }
}
//스트림을 사용한 코드
menu.parallelStream().filter(d -> d.getCalories() > 300)
                     .map(Dish::getName)
                     .collect(toList());

//람다 사용 전
Validator numericValidator = new Validator(new IsNumberic());
boolean b1 = numericValidator.validate("aaaa");
Validator lowerCaseValidator = new Validator(new IsAllLowwerCase());
boolean b2 = lowerCaseValidator.validate("bbbb");

//람다 사용 후
Validator numericValidator = new Validator((String s) -> s.matches("[a-z]+"));
boolean b1 = numericValidator.validate("aaaa");
Validator lowewrCaseValidator = new Validator((String s) -> s.matches("\\d+"));
boolean b2 = lowerCaseValidator.validate("bbbb");

//람다 사용 전
abstract class OnlineBanking {
    public void processCustomer(int id) {
        Customer c = Database.getCustomerWithId(id);
        makeCustomerHappy(c);
    }
    abstract void makeCustomerHappy(Customer c);
}
//람다 사용 후
public void processCustomer(int id, Consumer<Customer> makeCustomerHappy) {
    Customer c = Database.getCustomerWithId(id);
    makeCustomerHappy.accept(c);
}
new OnlineBankingLambda().processCustomer(1337, (Customer c) ->
            System.out.println("Hello " + c.getName());

//람다 사용 전
class Feed implements Subject {
    private final List<Observer> observers = new ArrayList<>();
    public void registerObserver(Observer o) {
        this.observers.add(o);
    }
    public void notifyObservers(String tweet) {
        observers.forEach(o -> o.notify(tweet));
    }
}
//람다 사용 후
f.registerObserver((String tweet) -> {
    if(tweet != null && tweet.contains("money")) {
        System.out.println("Breaking news in NY! " + tweet);
    }
});
f.registerObserver((String tweet) -> {
    if(tweet != null && tweet.contains("queen")) {
        System.out.println("Yet more news from London... " + tweet);
    }
});

//람다 사용 전
public class ProductFactory {
    public static Product createProduct(String name) {
        switch(name) {
            case "loan" : return new Loan();
            case "stock" : return new Stock();
            case "bond" : return new Bond();
            default : throw new RuntimeException("No such product " + name);
        }
    }
}
//람다 사용 후
Supplier<Product> loanSupplier = Loan::new; 
Loan loan = loanSupplier.get();

final static Map<String, Supplier<Product>> map = new HashMap<>();
static {
    map.put("loan", Loan::new);
    map.put("stock", Stock::new);
    map.put("bond", Bond::new);
}

public interface TriFunction <T, U, V, R> {
    R apply(T t, U u, V v);
}
Map<String, TriFunction<Integer, Integer, String, Product>> map = new HashMap<>();

@Test
public void testMoveRightBy() throws Exception {
    Point p1 = new Point(5, 5);
    Point p2 = p1.moveRightBy(10);
    assertEquals(15, p2.getX());
    assertEquals(5, p2.getY());
}

public class Point {
    public final static Comparator<Point> compareByXAndThenY = 
        comparing(Point::getX).thenComparing(Point::getY);
    ...
}

@Test
public void testComparingTwoPoints() throws Exception {
    Point p1 = new Point(10, 15);
    Point p2 = new Point(10, 20);
    int result = Point.compareByXAndThenY.compare(p1, p2);
    assertTrue(result < 0);
}

public static List<Point> moveAllPointsRightBy(List<Point> points, int x) {
    return points.stream()
                 .map(p -> new Point(p.getX() + x, p.getY()))
                 .collect(toList());
}

@Test
public void testMoveAllPointsRightBy() throws Exception {
    List<Point> points = 
            Arrays.asList(new Point(5, 5), new Point(10, 5));
    List<Point> expectedPoints = 
            Arrays.asList(new Point(15, 5), new Point(20, 5));
    List<Point> newPoints = Point.moveAllPointsRightBy(points, 10);
    assertEquals(expectedPointes, newPoints);
}