import java.lang.management.*;

/* Example of counting cpu/system/user time.
 * Use the getCpuTime/getUserTime/getSystemTime to capture the timestamp.
 * Capture timestamp before action.
 * Capture timestamp after action.
 * Your running time is between before-action timestamp and after-action timestamp.
 * See example in method work().
 * Tested with Java 11.
 */

public class Timer {

  protected long captureTime;
  protected long runningTime;

  public Timer() {
  }

  public void foo() {
    int s = 0;
    for(int i=0; i<1000000; i++) {
      s += 1;
    }
  }

  public void work() {
    captureTime = getCpuTime();
    foo();
    System.out.println("CPU time: " + (getCpuTime() - captureTime));
  }
  
  /** Get cpu time in nanoseconds. */
  public long getCpuTime() {
    ThreadMXBean bean = ManagementFactory.getThreadMXBean( );
    if ( ! bean.isThreadCpuTimeSupported( ) )
      return 0L;
    return bean.getThreadCpuTime(java.lang.Thread.currentThread().getId());
  }

  /** Get user time in nanoseconds. */
  public long getUserTime( long[] ids ) {
    ThreadMXBean bean = ManagementFactory.getThreadMXBean( );
    if ( ! bean.isThreadCpuTimeSupported( ) )
      return 0L;
    return bean.getThreadUserTime(java.lang.Thread.currentThread().getId());
  }

  /** Get system time in nanoseconds. */
  public long getSystemTime( long[] ids ) {
    ThreadMXBean bean = ManagementFactory.getThreadMXBean( );
    if ( ! bean.isThreadCpuTimeSupported( ) )
      return 0L;
    return bean.getThreadCpuTime(java.lang.Thread.currentThread().getId()) + bean.getThreadUserTime(java.lang.Thread.currentThread().getId()); 
  }

  public static void main(String[] args) {
    new Timer().work();
  }
}