How to read propositional logic symbols as input using Java Scanner?

Question

 Scanner in = new Scanner(System.in,"UTF-8");
 System.out.println(in.next());

If I paste ∧, I receive ? as output to the console. Can someone explain what I can do to properly read logic symbols like this? I'm using NetBeans 8.0.1.

Thanks.

Answer 1

The problem is not with entering the character, but rather with printing it to console. Your console does not appear to support the code point \u2227 of ∧, so it prints a question mark instead.

You should test if console lets you input ∧ correctly by printing the numeric representation of the character that you read, like this:

Scanner in = new Scanner(System.in,"UTF-8");
String s = in.next();
if (s.length() != 0) {
    System.out.println((int)s.charAt(0));
}

If 8743 gets printed, you could process the character internally: comparisons like this

if (s.equals("∧")) {
    ...
}

will work correctly.

Otherwise, you should switch to using characters from the first code page, i.e. ^ instead of ∧

Answer 2

I think your terminal encoding ( IDE or command line ) might not be UTF-8 so when it converts you see the difference.

I just tried your code and got ∧ back.

Do an echo $LC_CTYPE or echo $LANG to check it.

Read this How to read a text file with mixed encodings in Scala or Java? and http://docs.oracle.com/javase/7/docs/api/java/nio/charset/CharsetDecoder.html
for working with different encodings.