[SOLVED] Is it my math or my logic/code? Number Formatting difficulties

[Brian LaRue]

Hey all, I can't decide what's going wrong here. I'm trying to write a program (for an assignment at school) which times how long the process takes to search a list. I can get the program to run, but I'm getting unexpected results. It's always telling me that it takes 0 ms to run. I don't know if it's my math, the formatting of the result, or somewhere in my program logic that's producing these results. Here's what I've got so far:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
public class ArrayTimer {
    public static void main(String[] args) {
    
        String[] product = new String[19];
        int[] amount = new int[19];
        long startTime;
        long endTime;
        long responseTime;
        BufferedReader reader = null;
        String lookupName = "";
boolean namefound = false;
 
        product[0] = "IPOD";
        product[1] = "THINKPAD";
        product[2] = "MACBOOK";
        product[3] = "VAIO";
        product[4] = "ATARI";
        product[5] = "COMMODORE";
        product[6] = "PCJR";
        product[7] = "MACBOOKPRO";
        product[8] = "MACBOOKAIR";
        product[9] = "IPHONE";
        product[10] = "ZUNE";
        product[11] = "BLACKBERRY";
        product[12] = "IDEABOOK";
        product[13] = "BLACKJACK";
        product[14] = "PENCIL";
        product[15] = "PAPER";
        product[16] = "ABACUS";
        product[17] = "STONETABLET";
        product[18] = "TABLETPC";
    
        amount[0] = 52;
        amount[1] = 35;
        amount[2] = 23;
        amount[3] = 39;
        amount[4] = 2;
        amount[5] = 1;
        amount[6] = 2;
        amount[7] = 99;
        amount[8] = 3;
        amount[9] = 44;
        amount[10] = 29;
        amount[11] = 59;
        amount[12] = 2;
        amount[13] = 43;
        amount[14] = 3;
        amount[15] = 1;
        amount[16] = 13;
        amount[17] = 22;
        amount[18] = 98;
 
try {
            reader = new BufferedReader(new InputStreamReader(System.in));
            System.out.print("Enter a product name to look up: ");
            lookupName = reader.readLine().trim();
            lookupName = lookupName.toUpperCase();
            startTime = System.currentTimeMillis();
 
            for(int d = 0; d < product.length; d++) {
                if(product[d].startsWith(lookupName)) {
                    System.out.println("You are looking for: " + product[d]);
                    System.out.println(product[d] + "'s were found.");
                    System.out.println("We have " + amount[d] + " of them.");
                    endTime = System.currentTimeMillis();
                    responseTime = (endTime - startTime);
                    System.out.println("Total time: " + responseTime + " ms");
                    namefound = true;
                    break;
                }
            }
 
            if(!namefound) {
                System.out.println("Sorry that name could not be found");
            }
 
        } catch(Exception e) {
            System.out.println(e.toString());
        } // end of try/catch
    } // end of main
} // end of class

Where could it be? Ive read the javadocs and discovered that currentTimeMillis() returns a long, so Ive declared the variables as such (to be large enough to handle them). I'm sure there's a better collection, implementation but as this is for an assignment, I have no choice but to use this particular set up. Either that or is my Core2 Duo laptop so smoking that it takes a nanosecond to locate it?

TIA

[ February 26, 2008: Message edited by: Brian LaRue ]
[ February 26, 2008: Message edited by: Brian LaRue ]

[Jesper de Jong]

At first sight it looks like there's nothing wrong with your program.

You're looking up the product in an array of strings that contains 19 elements. This most likely takes only a fraction of a millisecond, that's why you see "0 ms". Note that the precision of the timer that you query with System.currentTimeMillis(); depends on the operating system. For some versions of Windows, the precision can be as low as about 55 ms - so if you do anything that takes less than 55 ms, you can't time it accurately with this timer.

If you're using Java 5 or newer, you could try using System.nanoTime(), which possibly uses a more precise timer.

[Brian LaRue]

Well thanks for the suggestion of the System.nanoTime() method. I was underwear of that one and now I'm getting something other than "0 ms", which is what I ultimately wanted. It's giving me an output of: "Total Time: 781359 ms". I know the ms isn't true but that's an easy fix. The actual time changes depending on which product I choose to search for. That's neat!

How can I convert the nano seconds to seconds? I'm getting a possible loss of precsion here. I'm guessing that you have to cast the long down into a double? Or would float be more appropriate? I would like it to say "Total Time: 0.000781359 seconds". I read that a nano second is like multiplying your answer by 0.000000001 or 10^-9.

long startTime;
long endTime;
long responseTime;
[...]
startTime = System.nanoTime();
[...]
endTime = System.nanoTime();
responseTime = (endTime - startTime);
double response = (double)(responseTime * 0.000000001);
System.out.print("Total Time: " + response + " seconds.");

gives me the "possible loss of precision" compiler error. What am I doing wrong now?

Thanks again

[Bryce Martin]

Try using BigDecimal. Its made just for this occasion

Try looking here...

Hope this helps.

[Campbell Ritchie]

Alternative to BigDecimal:

System.out.printf("It took %d.%09d seconds%n", nanoSeconds / 1000000000, nanoSeconds % 1000000000);

You can alter the numbers to get milliseconds or microseconds.

[Brian LaRue]

Sweet! Thanks, I tried the printf() while tailoring it to my specific needs, it works! Thanks for everyone's help.