Framework-level interface defining an amount of time, such as "6 hours", "8 days" or "2 years and 3 months". !(p) This is the base interface type for amounts of time. An amount is distinct from a date or time-of-day _in that it is not tied to any specific point on the time-line. !(p) The amount can be thought of as a {@code Map} of {@link TemporalUnit} to {@code long}, exposed via {@link #getUnits()} and {@link #get(TemporalUnit)}. A simple case might have a single unit-value pair, such as "6 hours". A more complex case may have multiple unit-value pairs, such as "7 years, 3 months and 5 days". !(p) There are two common implementations. {@link Period} is a date-based implementation, storing years, months and days. {@link Duration} is a time-based implementation, storing seconds and nanoseconds, but providing some access using other duration based units such as minutes, hours and fixed 24-hour days. !(p) This interface is a framework-level interface that should not be widely used _in application code. Instead, applications should create and pass around instances of concrete types, such as {@code Period} and {@code Duration}.