Thread: Making a countdown timer using the currentTimeMillis method

Hey guys,

Recently I made the decision to learn Java programming on my own (I only bought a book, no course). So far I've covered the following relevant topics:
-Elementary Programming: Identifiers, Variables, Data types...
-Selections: boolean, if (else if, else) statements, logical operators, switch statements...
-Loops: while, do-while, for, nested loops, keywords break and continue... (=> Currently doing the exercises of this chapter).

In one of the last exercises of the latter chapter I'm asked to make a countdown timer. The only method to capture time the book has covered yet is the currentTimeMillis method in the System class.
I'm aware this problem probably can be solved in an easier and more efficient way using the Timer class, but imagine I follow the book strictly and I have never heard of it.

So far I have tried a number of things, without succes obviously, this is the best I came up with:

import java.util.Scanner;
	public class Exercise4_43 {
		public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
 
		System.out.print("Enter the number of seconds: ");
		int interval = input.nextInt();
		long startTime = System.currentTimeMillis();
		long endTime = System.currentTimeMillis() + (interval * 1000);
 
		while (System.currentTimeMillis() < endTime) {
			if ((endTime - System.currentTimeMillis()) % 1000 == 0){
				System.out.println(((endTime - System.currentTimeMillis()) / 1000) + " seconds remaining.");
				}
			}
		System.out.println("Stopped.");
	}
}

When I run the program and e.g. enter 10 as input I get the following output:

10 seconds remaining
//1 second later
9 seconds remaining
9 seconds remaining
9 seconds remaining
9 seconds remaining
//another second later
8 seconds remaining
8 seconds remaining
8 seconds remaining
8 seconds remaining
//another second later
7 seconds remaining
7 seconds remaining
7 seconds remaining
7 seconds remaining

....

0 seconds remaining
Stopped.

Can someone please give me a hint so I can solve this problem? (Please, don't give a possible solution, if I can't solve the problem myself I miss the opportunity to acquire some extra insight in this kind of problems).
Thanks in advance!

Cheers
Michael

Excuse me for not being clear enough explaining the problem.
The timer works fine, but why does it give every second 3-4 times the same output instead of just showing it once every second?

Thank you for your respons! Although I couldn't figure out why the program kept repeating the same output, I found another possible solution.
I got lost of the remainder operator and tried something else.

import java.util.Scanner;
public class Exercise4_43{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
 
		System.out.print("Enter the number of seconds: ");
		int interval = input.nextInt();
 
		long startTime = System.currentTimeMillis() / 1000;
		long endTime = startTime + interval;
 
		while (System.currentTimeMillis() / 1000 < endTime) {
			while (startTime != System.currentTimeMillis() / 1000) {
				startTime += 1;
				if (endTime - startTime > 1)
					System.out.println(endTime - startTime + " seconds remaining.");
				else if (endTime - startTime == 1) {
					System.out.println("1 second remaining.");
					}
				}
			}
		System.out.println("Time up.");
		}
	}

Now the programs works properly. Only too bad of the precison loss of the first second... //(long / 1000)

Yes. Every time I wanted to print the remaining value I used: (endTime - System.currentTimeMillis()) / 1000).
Once printed, 3-4 identical lines with the remaining seconds t appeared. One second later, another 3-4 identical lines with the t-1 remaining seconds appeared.
My processor is an Intel Core i3 CPU 530 @ 2.93 GHz, so far from high-end. I doubt this would be the cause of the problem because tons of PC's are faster than mine.
Or maybe no one has tried to put a remainder in their algorithm?

Thanks man, I didn't know that.
Lucky for me I tried something else, otherwise I would still be fooling around with the remainder operator.

Dear Michael, I don't know if you already found the answer,so sry if i repeat something already written, but i was programming the same exercise myself and found your method really useful! Just added a few lines to complete! Here it is!
import java.util.Scanner;

public class Exercise_4_43 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the number of seconds:");
int seconds = input.nextInt();
long startTime = System.currentTimeMillis();
long endTime = System.currentTimeMillis() + (seconds * 1000);
long temp = startTime + 1000 ;
System.out.print(seconds + " seconds remaining.\n" );
while (startTime < endTime) {
if (startTime == temp) {
seconds--;
System.out.print(seconds + " seconds remaining.\n");
temp += 1000;
}
startTime = System.currentTimeMillis();
}
System.out.println("Stopped.");
}
}