Why is the output always infinity?

Question

I wrote a simple command-line program for figuring out how long it will take to transfer a large file via a given interface. I don't understand why, but it always produces output like this: It will take Infinity seconds or Infinity minutes to transfer 10.0 gigabytes/10240.0 megabytes.

I don't understand why it's giving me that output.

import java.util.Scanner;

public class TransferTime {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double speed = 0;
        double gigabytes = 10;
        System.out.println("This will help you find out how long it will take to transfer a file");
        System.out.println();

        System.out.println("How many gigabytes do you want to transfer?");
        gigabytes = input.nextDouble();

        System.out.println("Enter 2 for USB 2, 3 for USB 3, f for FireWire 800 or t for Thunderbolt");
        String connection = input.next();
        System.out.println();
        if (connection == "2") {
            speed = 480;

        } else if (connection == "f")
            speed = 800;

        else if (connection == "3") {
            speed = 625;
        } else if (connection == "f") {
            speed = 100;
        } else if (connection == "t") {
            speed = 1280;
        }

        double megabytes = gigabytes * 1024;
        double seconds = megabytes / speed;
        double minutes = seconds / 60;

        System.out.println("It will take " + seconds + " seconds or " + minutes
                + " minutes to transfer " + gigabytes + " gigabytes/"
                + megabytes + " megabytes");
        input.close();

    }
}

The error is here: `connection == "2"`. It should be `connection.equals("2");`. Marked as duplicate. — Luiggi Mendoza, Apr 27 '15 at 19:53
Also note: You (try to) compare `connection` to "f" in two different places, and give two different divisors. — Solomon Slow, Apr 27 '15 at 19:56

score 2 · Answer 1 · answered Apr 27 '15 at 19:52

2

Dividing by 0 will give you infinity. And you are dividing by 0 because speed remains 0, since all your conditions are false (hint - don't compare Strings with ==).

answered Apr 27 '15 at 19:52

Eran

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Thank you! This worked! This will also be helpful in the future. I just wish I learned this earlier. I guess I didn't bother to find out about it until now because most of my programming until now hasn't involved Strings. – Jblagden Apr 27 '15 at 21:45

Why is the output always infinity?

1 Answers1