What Is a Code Review and Why Teams Do It

Direct Answer

A code review is when a peer examines your code changes before they merge into the shared codebase. Teams do it to catch bugs early, enforce consistent standards, and spread knowledge so no single person is the only one who understands a system.

Code Example

// Pull Request: Add order validation before payment processing
// Context: Customers were able to submit orders with negative quantities

@Service
public class OrderService {
    private final PaymentGateway paymentGateway;
    private final OrderRepository orderRepository;

    public OrderService(PaymentGateway paymentGateway, OrderRepository orderRepository) {
        this.paymentGateway = paymentGateway;
        this.orderRepository = orderRepository;
    }

    public Order processOrder(OrderRequest request) {
        // Validation added to catch business rule violations early
        if (request.quantity() <= 0) {
            throw new InvalidOrderException("Quantity must be positive");
        }
        if (request.totalAmount().compareTo(BigDecimal.ZERO) <= 0) {
            throw new InvalidOrderException("Order total must be positive");
        }

        var order = new Order(request.productId(), request.quantity());
        var payment = paymentGateway.charge(request.totalAmount());

        order.setPaymentId(payment.id());
        return orderRepository.save(order);
    }
}

A clear PR description plus a small, focused diff like this is exactly what makes a change quick to review.

Common Mistakes & Pitfalls

• Skipping review for small changes: Freshers think one-line fixes don't need review, but small changes often have big impacts. A logging level change can flood production logs and fill disk space. A single character typo in a SQL query can corrupt data.
• Treating review as personal criticism: When a reviewer points out issues, freshers feel attacked and get defensive. Code review targets the code, not you. A comment saying your method is hard to understand isn't saying you're a bad developer—it's helping you write clearer code.
• Waiting too long to submit: Freshers work on a feature for two weeks, then submit a massive 2000-line PR. By then, requirements might have changed, merge conflicts are guaranteed, and reviewers can't give thorough feedback on that volume. Submit work incrementally.