public class TimeExample
{
	  static long someFunction(int n)
	  {
	    long x=0;
	    //this code look familiar?
	    for(int i=0;i<n;i++) for(int j=1;j<i*i;j++) if((j%i)==0) for(int k=0;k<j;k++) x++;
	    return x;
	  }
	  
	  public static void main(String[] args)
	  {
		  //call System.currentTimeMillis() to get the current time (in ms)
		  System.out.println("The current time is"+System.currentTimeMillis()+" milliseconds since Jan 1 1970\n");
		  
		  int n=200;
		  long start,end;
		  long timeTaken;

		  //to measure the time taken of a block of code, record the time before and after, then use the difference
		  start=System.currentTimeMillis();
		  System.out.println("Test 1 starting at "+start);
		  someFunction(n);
		  end=System.currentTimeMillis();
		  System.out.println("Ending at "+end);
		  timeTaken=end-start;
		  System.out.println("Time taken: "+timeTaken+" milliseconds\n");
		  
		  //precise as computers are, in reality numerous factors govern run-time, and make it appear a bit 'random'
		  //  to get a more accurate estimate, run a bunch of tests and take the average
		  int times=10;
		  start=System.currentTimeMillis();
		  System.out.println("Test 2 starting at "+start);
		  for(int i=0;i<times;i++) someFunction(n);
		  //technically, we're confounding our results slightly by including the 'for' stuff in the timing
		  //  but in this case it's so insignificant that it shouldn't matter.
		  //if we were to measure something very fast (e.i. 'x++;'), the looping & call to currentTimeMillis() would 
		  //  completely dominate the time taken, completely skewing our estimate.
		  end=System.currentTimeMillis();
		  System.out.println("Ending at "+end);
		  timeTaken=(end-start)/times;
		  System.out.println("Time taken per iteration on average: "+timeTaken+" milliseconds");

		  ///////////////////////////////////////////////////
		  ///////////////////////////////////////////////////
		  //and now for something completely different: we're going to time the insertion of 50000 elements into an ArrayList
		  //we'll start by adding them to the end; constant time
		  int number=10000;
		  MyArray<Integer> arr=new MyArray<Integer>();
		  start=System.currentTimeMillis();
		  for(int i=0;i<number;i++) arr.add(new Integer(i)); //add to end
		  end=System.currentTimeMillis();
		  timeTaken=end-start;
		  System.out.println("\nTime taken for "+number+" adds: "+timeTaken+" milliseconds");
		  
		  //now we'll add them to the beginning & shifting over; linear time
		  arr=new MyArray<Integer>();
		  start=System.currentTimeMillis();
		  for(int i=0;i<number;i++) arr.addToStart(new Integer(i)); //add at the start
		  end=System.currentTimeMillis();
		  timeTaken=end-start;
		  System.out.println("Time taken for "+number+" adds: "+timeTaken+" milliseconds");
		  
		  //the moral of the story: it can matter significantly *how* you use your datastructures for timing; 
		  //  inserting elements in order in a bst will be quite different from inserting randomly
	  }
}