Builder Pattern (Item 2)

item2.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;
  }
}