Item2:Consider a builder when faced with many constructor parameters
当构造方法有多个参数时，可以考虑使用builder方式进行处理。
实例代码：
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{
//以下两个参数是必须的
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 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;
}
}
使用方式：
public class Test {
public static void main(String[] args) {
NutritionFacts nf = new NutritionFacts.Builder(200, 80)
.calories(100).sodium(35).carbohydrate(20).build();
}
}