scanner.next() does not stop

Question

public class ElectronicCounter {

    public ElectronicCounter(User user)throws IOException{
        Scanner scanner = new Scanner(System.in);
        boolean done = false;
        loginName = user.getName();

        System.out.println("--------------------------------------------------------");
        System.out.println("Welcome to the Electronic-Sales Counter! ");

        while(!done){
            try{
                System.out.print("Please enter '1' to record sales or '2' to exit:");
                input = scanner.nextLine();
                System.out.println("bug");
                if(input=="1"){
                    System.out.println("Please enter a list of purchasing-product ID and number");
                    done = true;
                }
                else if(input=="2"){
                    System.out.println("<LOG> User " +loginName+ " has successfully logged off! ");
                    done = true;
                }
                else{
                    System.out.println("<LOG> Invalid command");
                }
            }
            catch (NoSuchElementException e){
                System.out.println("<LOG> No Such Element");
            }
            catch (IllegalStateException e){
                System.out.println("<LOG> IllegalState");
            }
        }
        scanner.close();
    }

    static String loginName;
    static String input;
}

The scanner doesn't stop to search the token when scanner.nextLine() is computed. I would like to ask how can I stop the scanner to wait input??Thanks

score 1 · Accepted Answer · answered Feb 22 '14 at 08:29

1

NEVER compare strings using ==. When using == to compare string objects, you are not comparing it's values but it's references.

Always compare using the equals method.

input.equals("2");

answered Feb 22 '14 at 08:29

Kuba Spatny

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it's better to use `"2".equals(input)`, because in such a case you can't get NPE – nikis Feb 22 '14 at 08:31
@nikis I am pretty sure that `nextLine()` doesn't return null, it throws a `NoSuchElementException` or `IllegalStateException`. – Kuba Spatny Feb 22 '14 at 08:34
yep, but I'm talking about general case – nikis Feb 22 '14 at 08:36
@nikis in that case, you're right :) But note that sometimes you could prefer to know whether the string is null, as said in this answer: http://stackoverflow.com/a/20521058/1732709 – Kuba Spatny Feb 22 '14 at 08:40
but the dead loop still exists even i change it to input.equals("1") and input.equals("2") – user3340095 Feb 22 '14 at 16:00
@user3340095 and is the line `done = true;` ever executed? – Kuba Spatny Feb 22 '14 at 16:07
No, when the program executes scanner.nextLine(), the program will jump to NoSuchElementException – user3340095 Feb 22 '14 at 16:13

scanner.next() does not stop

1 Answers1