StopwatchCPU.java

/******************************************************************************
 *  Compilation:  javac StopwatchCPU.java
 *  Execution:    none
 *  Dependencies: none
 *
 *  A version of Stopwatch.java that measures CPU time on a single
 *  core or processor (instead of wall clock time).
 *
 ******************************************************************************/

 import java.lang.management.ThreadMXBean;
 import java.lang.management.ManagementFactory;
 
 /**
  *  The {@code StopwatchCPU} data type is for measuring
  *  the CPU time used during a programming task.
  *
  *  See {@link Stopwatch} for a version that measures wall-clock time
  *  (the real time that elapses).
  *
  *  @author Josh Hug
  *  @author Robert Sedgewick
  *  @author Kevin Wayne
  */
 
 public class StopwatchCPU {
     private static final double NANOSECONDS_PER_SECOND = 1000000000;
 
     private final ThreadMXBean threadTimer;
     private final long start;
 
     /**
      * Initializes a new stopwatch.
      */
     public StopwatchCPU() {
         threadTimer = ManagementFactory.getThreadMXBean();
         start = threadTimer.getCurrentThreadCpuTime();
     }
 
     /**
      * Returns the elapsed CPU time (in seconds) since the stopwatch was created.
      *
      * @return elapsed CPU time (in seconds) since the stopwatch was created
      */
     public double elapsedTime() {
         long now = threadTimer.getCurrentThreadCpuTime();
         return (now - start) / NANOSECONDS_PER_SECOND;
     }
 }