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1 public class Main5{ 2 3 private final int servingSize; 4 5 private final int servings; 6 7 private final int calories; 8 9 private final int fat;10 11 private final int sodium;12 13 private final int carbohydrate;14 15 public static class Builder{16 17 private final int servingSize;18 19 private final int servings;20 21 private int calories = 0;22 23 private int fat = 0;24 25 private int sodium = 0;26 27 private int carbohydrate = 0;28 29 public Builder(int servingSize,int servings){30 this.servingSize = servingSize;31 this.servings = servings;32 }33 34 public Builder calories(int calories){35 this.calories = calories;36 return this;37 }38 39 public Builder fat(int fat){40 this.fat = fat;41 return this;42 }43 44 public Builder sodium(int sodium){45 this.sodium = sodium;46 return this;47 }48 49 public Builder carbohydrate(int carbohydrate){50 this.carbohydrate = carbohydrate;51 return this;52 }53 54 public Main5 build(){55 return new Main5(this);56 }57 }58 59 private Main5(Builder builder){60 servingSize = builder.servingSize;61 servings = builder.servings;62 calories = builder.calories;63 fat = builder.fat;64 sodium = builder.sodium;65 carbohydrate = builder.carbohydrate;66 }67 }
当一个类有很多属性
有很多的熟悉可以是默认的值的时候
可以通过写多个不同参数的构造方法去实现
但是很麻烦
这种方式设计上很灵活
基本上可以上任意的组合见Effective java （中文第二版） 第11页