Effective Java 英文 第二版 读书笔记 Item 2:Consider a builder when faced with many constructor parameters.

package builderManyPara;

//JavaBeans Pattern - allows inconsistency,mandates mutability 
public class NutritionFactsBean {
    // Parameters initialized to default values(if any)
    // required
    private int servingSize = -1;
    private int servings = -1;

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

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

    public int getServingSize() {
        return servingSize;
    }

    public void setServingSize(int servingSize) {
        this.servingSize = servingSize;
    }

    public int getServings() {
        return servings;
    }

    public void setServings(int servings) {
        this.servings = servings;
    }

    public int getCalories() {
        return calories;
    }

    public void setCalories(int calories) {
        this.calories = calories;
    }

    public int getFat() {
        return fat;
    }

    public void setFat(int fat) {
        this.fat = fat;
    }

    public int getSodium() {
        return sodium;
    }

    public void setSodium(int sodium) {
        this.sodium = sodium;
    }

    public int getCarbohydrate() {
        return carbohydrate;
    }

    public void setCarbohydrate(int carbohydrate) {
        this.carbohydrate = carbohydrate;
    }

    public static void main(String[] args) {
        NutritionFactsBean nutritionFactsBean=new NutritionFactsBean(240, 8);
        nutritionFactsBean.setFat(8);
    }
}

package builderManyPara;

//Builder Pattern
public class NutritionFactsBuilder {

    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 implements Builders<NutritionFactsBuilder> {
        // Required parameters
        private final int servingSize;
        private final int servings;

        // Optional parameters - initialized to default values
        private int calories = 0;
        private int fat = 0;
        private int sodium = 0;
        private int carbohydrate = 0;

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

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

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

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

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

        public NutritionFactsBuilder build() {
            return new NutritionFactsBuilder(this);
        }

    }

    private NutritionFactsBuilder(Builder builder) {
        servingSize = builder.servingSize;
        servings = builder.servings;
        calories = builder.calories;
        fat = builder.fat;
        sodium = builder.sodium;
        carbohydrate = builder.carbohydrate;
    }

    public static void main(String[] args) {
        NutritionFactsBuilder nutritionFacts = new NutritionFactsBuilder.Builder(240, 8)
                .calories(100).sodium(35).build();
    }
}

package builderManyPara;

//A builder for objects of type
public interface Builders<T> {
    public T build();
}