ending a while loop condition

Question

I'm trying to make a simple program that uses a scanner for input and has a while loop that continues taking input until an end character is entered. I want the scanner to take input and add a string to the stack list. I'm trying to figure out why this code doesn't terminate the while loop when a space is typed.

import java.util.Scanner;

public class ReverseString<E> {

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    Stack<String> stack = new Stack();

    //while(scan.hasNext() && !stack.equals(" ")){
 //       while(!scan.nextLine().equals("")){
    while (scan.hasNext()) {
        stack.push(scan.next());
        if (scan.equals(" ")) {
            break;
        }

    }

    System.out.print(stack.pop() + " ");


 }
}

see https://stackoverflow.com/questions/19509647/scanner-doesnt-see-after-space — Scary Wombat, Oct 30 '18 at 02:55

Bejond · Answer 1 · 2018-10-30T03:21:33.533

0

while (scan.hasNext()) {
    stack.push(scan.next());
    if (scan.equals(" ")) {
        break;
    }

}

change to

while (scan.hasNextLine()) {
    String value = scan.nextLine();
    if (" ".equals(value)) {
        break;
    }
    stack.push(value);
}

scan is a Scanner, it's not a String, scan.equals(" ") would always return false.

edited Oct 30 '18 at 03:21

answered Oct 30 '18 at 02:55

Bejond

1,188
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Good spotting with `scan.equals` but did you test it? – Scary Wombat Oct 30 '18 at 02:59
Thanks for point out. https://stackoverflow.com/questions/22458575/whats-the-difference-between-next-and-nextline-methods-from-scanner-class – Bejond Oct 30 '18 at 03:20

score 0 · Accepted Answer · answered Oct 30 '18 at 03:03

0

You should use nextLine instead

while (scan.hasNextLine()) {
    String nextInput = scan.nextLine();
    stack.push(nextInput );
    if (nextInput.equals(" ")) {
        break;
    }
}

answered Oct 30 '18 at 03:03

Scary Wombat

44,617
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This works. I tried the others and they didn't work. – Michael Fogarty Oct 30 '18 at 03:12
I did upvote. I'm not sure why but someone had previously downvoted it for some reason. Accepted as correct answer thanks. – Michael Fogarty Oct 30 '18 at 03:34

score -1 · Answer 3 · answered Oct 30 '18 at 02:55

You're doing,

if (scan.equals(" ")) {
    break;
}

which means you're comparing the Scanner object scan to a space. Try doing the following instead(you have to compare the scan.next() with a space):

import java.util.Scanner;

public class ReverseString<E> {

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    Stack<String> stack = new Stack();

    //while(scan.hasNext() && !stack.equals(" ")){
 //       while(!scan.nextLine().equals("")){
    while (scan.hasNext()) {
        String nextInput = scan.next();
        stack.push(nextInput );
        if (nextInput.equals(" ")) {
            break;
        }

    }

    System.out.print(stack.pop() + " ");


 }
}

ending a while loop condition

3 Answers3