time of execution

[Puneet N Vyas]

i have used time of execution class to know the time of execution of the operation,but upon running the program different times it gives different time of execution,can any one tell why it is happening or anyother way to get the time of execution

  /**
 * @(#)MiningExecutionTime.java
 *
 *
 * @author puneet vyas
 * @version 1.00 2008/4/16
 */
 
//for knowing the mining execution time in miliseconds
 

 //execution timer methods
    //for knowing the time of execution of the mining
  
   //end of timer methods for getting the mining duration 
 

public class MiningExecutionTime 
 
{
 public long start;
  public long end;
    public MiningExecutionTime() 
    {
    
    reset();
    
    }
    
    public void start() 
  {
    start = System.currentTimeMillis();
  }
 
  public void end() {
    end = System.currentTimeMillis();
  }
 
  public long duration(){
    return (end-start);
  }
 
  public void reset() {
    start = 0;  
    end   = 0;
  }
 
}/**
 * @(#)loop.java
 *
 *
 * @author 
 * @version 1.00 2008/5/9
 */
 

public class loop {
 
   
    
    public static void main(String args[])
    {
   
   MiningExecutionTime t1=new MiningExecutionTime();
   t1.start();
   for (int i = 0; i<1000; i++) 
   {
   System.out.println("time of execution");
   
   }
   t1.end();
   System.out.println("time of execution"+t1.duration());
   
    }
    
}  

thanks for support

[Joanne Neal]

How big a difference are you seeing in the times ? No program will have the same execution time every time it runs.

[Jesper de Jong]

Note that the accuracy of the timer used by System.currentTimeMillis() is not very good on some operating systems. So if you time very short events, you will not get very accurate time measurements if you use this.

If you're using Java 5 or newer, you could use System.nanoTime() instead, which will probably use a more accurate timer, but even that timer does not have a guaranteed accuracy.

[Bill Shirley]

The time of execution should not be expected to be a constant.

If you're playing video on your machine, and defragging the hard drive, it will effect other processes. All machines are running many, many processes, and they're all sharing the resources.