整理機能javaアイテム2用語

Telescotting Constructor Pattern(レイヤジェネレータアレイ単位)

public class Test{
	private final String fieldA;
    private String fieldB;
    private String fieldC;
    private String fieldD;
    
    public Test(String fieldA){ ... }
    public Test(String fieldA, String fieldB){ ... }
    public Test(String fieldA, String fieldB, String fieldC){ ... }
    public Test(String fieldA, String fieldB, String fieldC, String fieldD){ ... }
}

パラメータの順序を誤って変更した場合、コンパイラは気づかず、最終的には実行時に予想外の動作をします。

public class Test{
    private String fieldA;
    private String fieldB;
    
    public Test(String fieldA, String fieldB){ ... }
}

Test test = new Test(fieldB, fieldA); // 두 인자의 순서가 바뀜 하지만 컴파일 오류는 없음

public class Test{
	private String fieldA;
    private String fieldB;
    
    public Test(){ ... };
    
    public void setFieldA(String fieldA){ ... }
    public void setFieldB(String fieldB){ ... }
}

Test test = new Test();
test.setFieldA("");
test.setFieldB("");

ビルダー・モード(Builder Pattern)

public class NutritionFacts {
    private final int servingSize;
    private final int servings;
    private final int calories;
    private final int fat;
    private final int sodium;
    private final int carbohydrate;

    public static class Builder {
        private final int servingSize;
        private final int servings;

        private int calories = 0;
        private int fat = 0;
        private int sodium = 0;
        private int carbohydrate = 0;

        public Builder(int servingSize, int servings) {
            this.servingSize = servingSize;
            this.servings = servings;
        }

        public Builder calories(int val) {
            calories = val;
            return this;
        }

        public Builder fat(int val) {
            fat = val;
            return this;
        }

        public Builder sodium(int val) {
            sodium = val;
            return this;
        }

        public Builder carbohydrate(int val) {
            carbohydrate = val;
            return this;
        }
    }

    public NutritionFacts(Builder builder) {
        this.servingSize = builder.servingSize;
        this.servings = builder.servings;
        this.calories = builder.calories;
        this.fat = builder.fat;
        this.sodium = builder.sodium;
        this.carbohydrate = builder.carbohydrate;
    }
}

FLUENT APIまたはメソッドメカニズム

シミュレーションself-type習語(シミュレーションself-type慣用句)

public class SimulatedSelfTypeIdiomTest {
    public static abstract class Pizza {
        public enum Topping {HAM, MUSHROOM, ONION, PEPPER, SAUSAGE}

        final Set<Topping> toppings;

        abstract static class Builder<T extends Builder<T>> {
            EnumSet<Topping> toppings = EnumSet.noneOf(Topping.class);

            public T addTopping(Topping topping) {
                toppings.add(Objects.requireNonNull(topping));
                return self();
            }

            abstract Pizza build();

            // sub class는 이 method를 overriding하여
            // "this"를 반환하도록 해야 한다.
            protected abstract T self();
        }

        Pizza(Builder<?> builder) {
            // 불변식 보장을 위해 매개변수 복사
            toppings = builder.toppings.clone();
        }
    }

    public static class NYPizza extends Pizza {
        public enum Size {SMALL, MEDIUM, LARGE}

        private final Size size;

        public static class Builder extends Pizza.Builder<Builder> {
            private final Size size;

            public Builder(Size size) {
                this.size = Objects.requireNonNull(size);
            }

            @Override
            public NYPizza build() {
                return new NYPizza(this);
            }

            @Override
            protected Builder self() {
                return this;
            }
        }

        private NYPizza(Builder builder) {
            super(builder);
            size = builder.size;
        }
    }
}

コヒーレント戻りタイプ(共通戻りタイプ)

protected abstract T self();

@Override
protected Builder self() {
	return this;
}