Debugging & Logging

A real application logs instead of using System.out.println — logging can be turned on/off or filtered by severity without editing code, and includes a timestamp and source location automatically.

import java.util.logging.Logger;

class OrderService {
    private static final Logger log = Logger.getLogger(OrderService.class.getName());

    void placeOrder(String id) {
        log.info("Placing order " + id);
    }
}

In real projects, SLF4J with Logback is far more common than the built-in java.util.logging shown above, but the core idea — log levels (INFO, WARN, ERROR) instead of always printing — is the same either way.