Java精确测量代码运行时间 代码执行时间 纳秒 nanoTime 拂晓风起

Java精确测量代码运行时间：

        long startTime = System.nanoTime();  //開始時間
        for(int i = 0;i<10000;i++){
            ;
        }
        long consumingTime = System.nanoTime() - startTime; //消耗時間
        System.out.println(consumingTime);
        System.out.println(consumingTime/1000+"微秒");

JDK的解释：

public static long 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; 

返回：

The current value of the system timer, in nanoseconds.

自从：

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