Use the modern, immutable java.time package for handling dates and times.
Before Java 8, working with dates and times in Java using `java.util.Date` and `java.util.Calendar` was notoriously difficult and error-prone. These classes had mutable state, were not thread-safe, had poor API design, and used a confusing zero-based month index. The new Date and Time API, located in the `java.time` package, solves all of these problems. The new API is based on the ISO-8601 calendar system and is designed to be immutable and thread-safe. Immutability means that once a date or time object is created, it cannot be changed. Any modification operation, like adding a day, returns a new object, which makes the code much safer, especially in concurrent environments. The core classes of the new API are more intuitive. `LocalDate` represents a date without time (e.g., 2023-10-27). `LocalTime` represents a time without a date (e.g., 15:30:00). `LocalDateTime` combines both date and time but without a time zone. For time zone-aware date and time, you use `ZonedDateTime`. The API provides a rich set of methods for manipulating dates and times, such as `plusDays()`, `minusHours()`, etc., in a fluent and readable style. It also includes classes like `Duration` for measuring time in seconds and nanoseconds, and `Period` for measuring time in years, months, and days. Formatting and parsing dates and times is handled by the `DateTimeFormatter` class, which is also thread-safe. This modern API is a massive improvement and should always be used for any date/time logic in new Java applications.