本文解析了Java中的System.nanoTime方法，该方法提供纳秒级精度的时间戳，主要用于测量时间间隔而非确切时间点。文章强调了其在计算代码执行时间等场景中的正确使用方式，并指出其不适用于获取实际时间。
System.nanoTime只能用于计算时间差，不能用于计算时间的准确度（System.out.println(new Date(System.nanoTime()));这种是绝对错误的）。
Returns the current value of the most precise available system timer, in nanoseconds.
This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time. The value returned represents nanoseconds since some fixed but arbitrary time (perhaps in the future, so values may be negative). This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees are made about how frequently values change. Differences in successive calls that span greater than approximately 292 years (263 nanoseconds) will not accurately compute elapsed time due to numerical overflow.
For example, to measure how long some code takes to execute:
Returns:
The current value of the system timer, in nanoseconds.
Since:
1.5
long java.lang.System.nanoTime()Returns the current value of the most precise available system timer, in nanoseconds.
This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time. The value returned represents nanoseconds since some fixed but arbitrary time (perhaps in the future, so values may be negative). This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees are made about how frequently values change. Differences in successive calls that span greater than approximately 292 years (263 nanoseconds) will not accurately compute elapsed time due to numerical overflow.
For example, to measure how long some code takes to execute:
long startTime = System.nanoTime();
// ... the code being measured ...
long estimatedTime = System.nanoTime() - startTime;Returns:
The current value of the system timer, in nanoseconds.
Since:
1.5
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