Java学习笔记-02碰到多个构造器参数时要考虑用构建器[Java编程]

　　静态工厂和构造器有个共同的范围性:它们都不能很好地扩大到大量的可选参数.考虑用一个类表示包装食物表面显示的营养成份标签.这些标签中有几个域是必须的:每份的含量、每罐的含量以及每份的卡路里,还有超越20哥可选域:总脂肪量、饱和脂肪量、转化脂肪、胆固醇、钠等等.大大都产品在某几个可选域中城市有非零的值.

　　关于这样的类,应当用哪类构造器大概静态办法来编写呢?

　　1. 重叠构造器情势

　　[java]

　　// Telescoping constructor pattern - does not scale well!

　　public class NutritionFacts {

　　private final int servingSize; // (mL) required

　　private final int servings; // (per container) required

　　private final int calories; // optional

　　private final int fat; // (g) optional

　　private final int sodium; // (mg) optional

　　private final int carbohydrate; // (g) optional

　　public NutritionFacts(int servingSize, int servings) {

　　this(servingSize, servings, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories) {

　　this(servingSize, servings, calories, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat) {

　　this(servingSize, servings, calories, fat, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium) {

　　this(servingSize, servings, calories, fat, sodium, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium, int carbohydrate) {

　　this.servingSize = servingSize;

　　this.servings = servings;

　　this.calories = calories;

　　this.fat = fat;

　　this.sodium = sodium;

　　this.carbohydrate = carbohydrate;

　　}

　　public static void main(String[] args) {

　　NutritionFacts cocaCola =

　　new NutritionFacts(240, 8, 100, 0, 35, 27);

　　}

　　}

　　// Telescoping constructor pattern - does not scale well!

　　public class NutritionFacts {

　　private final int servingSize; // (mL) required

　　private final int servings; // (per container) required

　　private final int calories; // optional

　　private final int fat; // (g) optional

　　private final int sodium; // (mg) optional

　　private final int carbohydrate; // (g) optional

　　public NutritionFacts(int servingSize, int servings) {

　　this(servingSize, servings, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories) {

　　this(servingSize, servings, calories, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat) {

　　this(servingSize, servings, calories, fat, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium) {

　　this(servingSize, servings, calories, fat, sodium, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium, int carbohydrate) {

　　this.servingSize = servingSize;

　　this.servings = servings;

　　this.calories = calories;

　　this.fat = fat;

　　this.sodium = sodium;

　　this.carbohydrate = carbohydrate;

　　}

　　public static void main(String[] args) {

　　NutritionFacts cocaCola =

　　new NutritionFacts(240, 8, 100, 0, 35, 27);

　　}

　　}2. JavaBeans情势

　　[java]

　　// Telescoping constructor pattern - does not scale well!

　　public class NutritionFacts {

　　private final int servingSize; // (mL) required

　　private final int servings; // (per container) required

　　private final int calories; // optional

　　private final int fat; // (g) optional

　　private final int sodium; // (mg) optional

　　private final int carbohydrate; // (g) optional

　　public NutritionFacts(int servingSize, int servings) {

　　this(servingSize, servings, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories) {

　　this(servingSize, servings, calories, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat) {

　　this(servingSize, servings, calories, fat, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium) {

　　this(servingSize, servings, calories, fat, sodium, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium, int carbohydrate) {

　　this.servingSize = servingSize;

　　this.servings = servings;

　　this.calories = calories;

　　this.fat = fat;

　　this.sodium = sodium;

　　this.carbohydrate = carbohydrate;

　　}

　　public static void main(String[] args) {

　　NutritionFacts cocaCola =

　　new NutritionFacts(240, 8, 100, 0, 35, 27);

　　}

　　}

　　// Telescoping constructor pattern - does not scale well!

　　public class NutritionFacts {

　　private final int servingSize; // (mL) required

　　private final int servings; // (per container) required

　　private final int calories; // optional

　　private final int fat; // (g) optional

　　private final int sodium; // (mg) optional

　　private final int carbohydrate; // (g) optional

　　public NutritionFacts(int servingSize, int servings) {

　　this(servingSize, servings, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories) {

　　this(servingSize, servings, calories, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat) {

　　this(servingSize, servings, calories, fat, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium) {

　　this(servingSize, servings, calories, fat, sodium, 0);

　　}

　　public NutritionFacts(int servingSize, int servings,

　　int calories, int fat, int sodium, int carbohydrate) {

　　this.servingSize = servingSize;

　　this.servings = servings;

　　this.calories = calories;

　　this.fat = fat;

　　this.sodium = sodium;

　　this.carbohydrate = carbohydrate;

　　}

　　public static void main(String[] args) {

　　NutritionFacts cocaCola =

　　new NutritionFacts(240, 8, 100, 0, 35, 27);

　　}

　　}3. Builder情势,既能保证安全性,又能保证可读性.

　　[java]

　　// 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 {

　　// 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 carbohydrate = 0;

　　private int sodium = 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 carbohydrate(int val)

　　{ carbohydrate = val; return this; }

　　public Builder sodium(int val)

　　{ sodium = val; return this; }

　　public NutritionFacts build() {

　　return new NutritionFacts(this);

　　}

　　}

　　private NutritionFacts(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) {

　　NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8).

　　calories(100).sodium(35).carbohydrate(27).build();

　　}

　　}

　　// 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 {

　　// Required parameters

　　private final int servingSize;

　　private final int servings;

　　// Optional parameters - initialized to default values

　　private int calories = 0;