Item 2: Consider a Builder When Faced with Many Constructor Parameters

Key Concepts:

When a class has many optional parameters, constructors can become confusing and hard to read.

Solutions:

1. Telescoping Constructor Pattern (Not Recommended)

   Hard to maintain as parameters increase.

   public class NutritionFacts {
       private final int servingSize;
       private final int calories;
   
       public NutritionFacts(int servingSize) { this(servingSize, 0); }
       public NutritionFacts(int servingSize, int calories) { ... }
   }

2. JavaBeans Pattern (Mutable, not thread-safe)

   Allows inconsistency since the object is mutable.

   NutritionFacts nf = new NutritionFacts();
   nf.setServingSize(240);
   nf.setCalories(100);

3. Builder Pattern (Recommended)

   public class NutritionFacts {
       private final int calories;
       private final int fat;
   
       public static class Builder {
           private int calories = 0;
           private int fat = 0;
   
           public Builder calories(int val) { this.calories = val; return this; }
           public Builder fat(int val) { this.fat = val; return this; }
           public NutritionFacts build() { return new NutritionFacts(this); }
       }
   
       private NutritionFacts(Builder builder) {
           calories = builder.calories;
           fat = builder.fat;
       }
   }
   
   // Usage
   NutritionFacts nf = new NutritionFacts.Builder().calories(100).fat(5).build();