Duration & Period

Time spans come in two flavors, and Java models them with two separate types. Duration measures machine time in seconds and nanoseconds, suited to cache TTLs, flash-sale countdowns, and SLA windows. Period measures calendar time in years, months, and days, suited to free-trial lengths, subscription terms, and return windows. This lesson covers both, then walks through the daylight saving time trap that exists precisely because they are not interchangeable.