Object-oriented programming · interview question

In a class representing an e-commerce order, you want to ensure that the quantity of items is never negative. Which approach should you take to enforce this invariant?

Multiple choiceHardchapter-3-curatedpremiumoopinvariants-and-validation

java

class Order {
  private int quantity;
  public Order(int quantity) {
    if (quantity < 0) throw new IllegalArgumentException("Quantity cannot be negative");
    this.quantity = quantity;
  }
  public void setQuantity(int quantity) {
    if (quantity < 0) throw new IllegalArgumentException("Quantity cannot be negative");
    this.quantity = quantity;
  }
}

Use a static method to check quantity before every operation.Set the quantity field as public and trust external validation.Initialize the quantity to zero and never check it again.Use a private field for quantity and validate it in the constructor and all modifying methods.

Answer and explanation

Correct answer

D. Use a private field for quantity and validate it in the constructor and all modifying methods.

Why

Using a private field ensures that the quantity can only be accessed and modified through controlled methods. By validating in the constructor and all modifying methods, the class enforces its invariants, maintaining integrity.

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In a class representing an e-commerce order, you want to ensure that the quantity of items is never negative. Which approach should you take to enforce this invariant?

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