Metodedekomponering og ren kode

public class Main {
  // Entry point: reads like a story using small helpers
  public static void main(String[] args) {
    double subtotal = 120.00;
    double discountRate = 0.10; // 10% off
    double taxRate = 0.08;      // 8% tax

    double discounted = applyDiscount(subtotal, discountRate); // pure
    double taxed = addTax(discounted, taxRate);                 // pure
    double total = round2(taxed);                               // pure

    printReceipt(subtotal, discountRate, taxRate, total);       // I/O kept at edge
  }

  // Apply a percentage discount (pure)
  static double applyDiscount(double amount, double rate) {
    return amount - (amount * rate);
  }

  // Add a percentage tax (pure)
  static double addTax(double amount, double rate) {
    return amount + (amount * rate);
  }

  // Round to 2 decimals (pure)
  static double round2(double x) {
    return Math.round(x * 100.0) / 100.0;
  }

  // Handle printing separately (side effect)
  static void printReceipt(double subtotal, double discountRate, double taxRate, double total) {
    System.out.println("Subtotal: " + subtotal);
    System.out.println("Discount: " + (int)(discountRate * 100) + "%");
    System.out.println("Tax: " + (int)(taxRate * 100) + "%");
    System.out.println("Total: " + total);
  }
}