자바 프로그램 수행 시간 측정 하는 법 (성능 평가)

자바 프로그램 수행 시간 측정 하는 법 (성능 평가)

1. 사용 예제

public class NanoTimer {

    public static void main(String[] args) {


long starttime = System.nanoTime();// 시작점 시간 저장 save time when your code started

/*----------------------------------------
        코드 your codes
----------------------------------------*/

long endtime = System.nanoTime(); // 모든 코드가 실행되고 시간 저장 save time when your code ended

long estimatedTime = endtime - starttime; //시작점과 끝점을 계산하여 걸린 시간 측정 calculate the spending time of your code
System.out.println(estimatedTime); //걸린시간을 출력 show the time.



    }
}

2. 설명_비교

currentTimeMillis

-ms 밀리초 사용

-날짜와 관련된 시간 계산에 사용

-컴퓨터 시스템 시간 (외부 데이터) 사용

-현재시간부터 1970년 1월 1일까지 사이 시간을 측정

nanoTime

-ns 나노초 사용

-경과시간 계산에 사용

-컴퓨터 시스템 시간 (외부 데이터)과 무관

• currentTimeMillis

  public static long currentTimeMillis()

  Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.

  See the description of the class Date for a discussion of slight discrepancies that may arise between "computer time" and coordinated universal time (UTC).

  Returns:

  the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.

  See Also:

  Date

• nanoTime

  public static long nanoTime()

  Returns the current value of the running Java Virtual Machine's high-resolution time source, 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 origin time (perhaps in the future, so values may be negative). The same origin is used by all invocations of this method in an instance of a Java virtual machine; other virtual machine instances are likely to use a different origin.

  This method provides nanosecond precision, but not necessarily nanosecond resolution (that is, how frequently the value changes) - no guarantees are made except that the resolution is at least as good as that of currentTimeMillis().

  Differences in successive calls that span greater than approximately 292 years (2⁶³ nanoseconds) will not correctly compute elapsed time due to numerical overflow.

  The values returned by this method become meaningful only when the difference between two such values, obtained within the same instance of a Java virtual machine, is computed.

  For example, to measure how long some code takes to execute:

   long startTime = System.nanoTime();
   // ... the code being measured ...
   long estimatedTime = System.nanoTime() - startTime;

  To compare two nanoTime values

   long t0 = System.nanoTime();
   ...
   long t1 = System.nanoTime();

  one should use t1 - t0 < 0, not t1 < t0, because of the possibility of numerical overflow.

  Returns:

  the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds

  Since:

  1.5

API 페이지로 이동

3.설명_시간 단위

1초 

= 0.001초(밀리초ms) = 10^(-3) = 1/1,000

= 0.000001초(마이크로초㎲) = 10^(-6) =  1/1,000,000 

= 0.000000001초(나노초ns) = 10^(-9) = 1/1,000,000,000

= 0.000000000001초(피코초ps) = 10^(-12) = 1/1,000,000,000,000

= 0.000000000000001초(펨토초fs) = 10^(-15) = 1/1,000,000,000,000,000

= 0.000000000000000001초(아토초as)= 10^(-18) = 1/1,000,000,000,000,000,000

4. 결론

코드의 수행시간 측정에는 nanoTime을 사용하자.

currentTimeMillis메서드는 컴퓨터 시간을  날짜계산에 유리하다.