Comparing characters.

I am writing a code (a beginners code, i set myself targets for a simple program, and along the way i pick up all the extra details about java) and i want to be able to ask the user a yes or no answer and test that in a condition. Here is what i wrote (narrowed down to just the necessary code);

Code:

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import java.util.Scanner;

class choice {
    public static void main(String[] args) {
        System.out.println("(y/n):");
        Scanner scan = new Scanner(System.in);
        String ch = scan.nextLine();
        if (ch=="y") { System.out.println("you chose yes (y)"); }
        else if (ch=="n") { System.out.println("you chose no (n)"); }
        else { System.out.println("you didn't choose yes or no!"); }
    }
}

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This compiles perfectly well, but when i enter the y or n (or anything for that matter) it just passes to the else statement. Always. So i tried using char and all its ways, that didnt compile right. Then using int, which compiled, but--

Code:

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import java.util.Scanner;

class choice {
    public static void main(String[] args) {
        System.out.println("(y/n):");
        Scanner scan = new Scanner(System.in);
        int ch = scan.nextInt();
        if (ch=='y') { System.out.println("you chose yes (y)"); }
        else if (ch=='n') { System.out.println("you chose no (n)"); }
        else { System.out.println("you didn't choose yes or no"); }
    }
}

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This compiles correctly but throws up an exception (see below) when either n or y is selected:

Code:

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james@james-laptop:~/Desktop/coding/Jcoding/examples$ java choice
(y/n):
y
Exception in thread "main" java.util.InputMismatchException
        at java.util.Scanner.throwFor(Scanner.java:857)
        at java.util.Scanner.next(Scanner.java:1478)
        at java.util.Scanner.nextInt(Scanner.java:2108)
        at java.util.Scanner.nextInt(Scanner.java:2067)
        at choice.main(choice.java:7)

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am i comparing strings or characters incorrectly? (im using jdk on linux btw)

Thanks in advance.

You compare objects(which a string is) with equals. Chars can be compared with ==.

Try

Code:

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char c = 'y';
System.out.println(c == 'y');

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An InputMismatchException is thrown when the received input type does not match the desired input type. In this case you asked for an int, but inputted something that isn't an int.

ok, so we have ruled the bottom one out, there is still the matter of my original code, why wont it recognize my input if it is comparing a string to a string (supposedly)

Quote:

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Originally Posted by javajames

ok, so we have ruled the bottom one out, there is still the matter of my original code, why wont it recognize my input if it is comparing a string to a string (supposedly)

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Because you're asking for an int... hence nextInt().

Quote:

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the matter of my original code

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Please post the line(s) of code you're talking about.

what scanner is used with characters?

new code, based on others suggestions, cant get character scanner to work:

Code:

---

import java.util.Scanner;

class choice {
    public static void main(String[] args) {
        System.out.println("(y/n):");
        Scanner scan = new Scanner(System.in);
        char ch = scan.next();
        if (ch=='y') { System.out.println("you chose yes (y)"); }
        else if (ch=='y') { System.out.println("you chose no (n)"); }
        else { System.out.println("rrrrrrrrrgggggg, i hate you"); }
    }
}

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wait, scanner doesn't take char

Scanner#next() and Scanner#nextLine() return String objects. You should be able to easily extract the first (and only) character in the String via the String charAt(0) method.

ok, i've done it, but slightly crude isn't it? oh well, works!

Code:

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import java.util.Scanner;

class choice {
    public static void main(String[] args) {
        System.out.println("(y/n):");
        Scanner scan = new Scanner(System.in);
        String ch1 = scan.nextLine();
        char ch = ch1.charAt(0); //turns string into char
        if (ch=='y') { System.out.println("you chose yes (y)"); }
        else if (ch=='n') { System.out.println("you chose no (n)"); }
        else { System.out.println("rrrrrrrrrgggggg, i hate you"); }
    }
}

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thank you all

Quote:

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Originally Posted by javajames

ok, i've done it, but slightly crude isn't it? oh well, works!

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Why "crude"?

The main suggestion I'd have would be to change your String to lower case so that the code works even if the user presses Y or N, fix your indentation and use of braces so that the code is better spread out and readable, and check to be sure that the String is one char long. If no char's entered, you'll get an exception if you try to convert the 1st char in the String to a char. Also it's a good habit to close resources when done with them, including the Scanner object.

Code:

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      System.out.println("(y/n):");
      Scanner scan = new Scanner(System.in);
      String ch1 = scan.nextLine().toLowerCase();  // so it works if they enter Y or N
      if (ch1.length() == 1) {
        char ch = ch1.charAt(0); // turns string into char
        if (ch == 'y') {
            System.out.println("you chose yes (y)");
        } else if (ch == 'n') {
            System.out.println("you chose no (n)");
        } else {
            System.out.println("rrrrrrrrrgggggg, i hate you");
        }
      } else {  // if String is not one char long
        // print out error message
      }
      scan.close();  // may want to do this in the finally block of a try/catch block

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