EffectiveJava-第2条 遇到多个构造器参数时要考虑用构建器
遇到多个构造器参数时要考虑用构建器，且看最佳实践代码
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 parametersprivate final int servingSize;private final int servings;// Optional parameters - initialized to default valuesprivate 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;//对象域抛出异常if(this.fat>this.sodium){ throw new IllegalArgumentException("The fat must be little than sodium!!");}}public static void main(String[] args){NutritionFacts cocaCola = new NutritionFacts.Builder(240,8).calories(100).sodium(35).carbohydrate(27).build();System.out.println(cocaCola);}}