Input a single char.Comparisson failed

I input the character.The code goes into an infinite loop even though it is supposed(by me i admit) not to!

Code java:

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static char getInput() {
        boolean error = false;
        char c='n';
        do {
            try {
                error = false;
                Scanner in = new Scanner(System.in);
                 String s;
                 do{
                     s = in.nextLine();
                     c=s.charAt(0);
                 }while( c!='w' ||c!='W'||c!='a'||c!='A'||c!='a'||c!='s'||c!='S'||c!='d'||
                         c!='D');
            } catch (InputMismatchException e) {
                System.err.println("Unexpected IO ERROR: " + e.toString());
                error = true;
            }
        } while (error);
        return c;
    }

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The problem is that the comparison fails,because even though i typed w the loop starts again.

What i wanted to do is to get input from the user by the little arrows that are placed below the big enter of the keyboard,but i do not know how to do this(the only think that comes to mind is event on GUI,but i do not want to include GUI now).

Quote:

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The problem is that the comparison fails,because even though i typed w the loop starts again.

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Correct. So think about the condition you are using (because, clearly, it does not mean what you intend it to mean)

Code :

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while( c!='w' ||c!='W'||c!='a'||c!='A'||c!='a'||c!='s'||c!='S'||c!='d'||c!='D');

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It turns out that that the condition is always true. Suppose c is actually 'w'. In that case c!='w' is false, but the next bit - c!='W' - is true. So the whole disjunction (c!='w' OR c!='W' OR ...) is true.

On the contrary suppose c is something other than 'w'. In that case the first term of the disjunction (c!='w') is true, and therefore the whole disjunction is true. In fact faced with something-true OR something-else OR something-else OR... the runtime won't even look at the other parts of the disjunction.

So your condition is always true because some part or other always is.

A better condition would involve AND rather than OR.

Oh my god,what i missed there?? :/ Of course AND is what i need!

Could i do the same thing by letting the user hit the arrows i said in the first post instead of w,a,s,d?

Quote:

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Originally Posted by Samaras

Oh my god,what i missed there?? :/ Of course AND is what i need!

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It's easy to miss because in English we say "not p or q" to mean "not p and not q". Things are plainer when you wave your hand about to indicate parentheses. But you get strange looks...

Quote:

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Could i do the same thing by letting the user hit the arrows i said in the first post instead of w,a,s,d?

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No. Basically Java doesn't do character (or key) detection from the keyboard/console. It was one of the first "request for enhancements" registered with Sun: that was shortly after the Jurassic and I think we can safely conclude at this stage that it ain't gonna happen.

This is the sort of thing that is easily tested by making a little test program:

Code :

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import java.util.Scanner;
 
public class Test {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
            // read a line (there is no method to return a character straight away)
        String line = in.nextLine();
            // and examine it character by character
        for(char ch :line.toCharArray()) {
            System.out.println(ch);
        }
    }
}

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I had never noticed it before, but Scanner's behaviour when run at the command line is quite interesting. The up/down arrow keys maintain a history between runs of the program, which is an interesting security hole.

You have more options when writing a graphical (Swing or similar) application. Buttons can be provided or you can handle keys (arrows or letters) registering "handlers": methods that do the right thing when the appropriate gesture is made.

1-I am Greek so i do not think that it was english fault.

2-Yeah i noticed too,but not something special :/ Also the right and left do nothing.

Thanks anyway