Clocks and Time
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- Absolute Time - Represents a specific point in time given by milliseconds plus nanoseconds past some point in time fixed by the clock. For the default real-time clock the fixed point is the Epoch (January 1, 1970, 00:00:00 GMT)
- Relative Time - A value expressed as relative to some other time value (usually the current value). e.g. 10000 milliseconds.
- Standard Java only has a wall clock - calendar time. But real time systems require:
- A monotonic clock.
- A countdown clock.
- A CPU execution time clock - measures amount of CPU time consumed by a particular thread or object.
- Time is supported through the HighResolutionTime abstract class. Three implementing concrete classes - absolute, relative and rational.
- Clock is supported through an abstract Clock class.
