Check if the string contains other characters

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I am developing a project that works with logical expressions, for example receive as input:

((TvF->T)^(T->F))->(~F<->T)

then I do all the validation to remove blanks, replace -> for - and <-> for -.

How can I perform a validation on the expression string to check if the user has entered any other character than one of these:

(,T,v,F,->,<->,~,),^?
java

  • You either only detect or want to remove too?

  • Regex in the method String.matches( ... ) to check for invalid characters

  • I would like to detect only, to warn the user that he has entered an invalid expression. The Matches I would use in the case String.Matches("(Tvf ~"); for it to return if it found other things besides these characters in the string?

  • I don’t think this validation would be enough, because you will need to validate whether the expression is coherent as well; for example, validate that all parentheses have been closed and are correctly nested. I think you’ll need to implement a lexicon analyser.

1 answer

0

Just to validate whether the characters are valid you can do something like this:

    String operation = "((TvF->T)^(T->F))->(~F<->T)";
    Set<String> validStrings = new HashSet<String>(
        Arrays.asList(new String[]{ "(", "T", "v", "F", "->", "<->", "~", ")", "^", "?" })
        );
    Set<Character> combinedChars = new HashSet<Character>(
        Arrays.asList(new Character[]{ '-', '<' })
        );

    boolean isValidOp = true;
    StringBuilder subString = new StringBuilder();
    for (int i = 0; i < operation.length(); i++) {
        subString.append(operation.charAt(i));
        if (validStrings.contains(subString.toString())) {
            subString = new StringBuilder();
        } else {
            if (!combinedChars.contains(operation.charAt(i))) {
                isValidOp = false;
                break;
            }
        }
    }

    System.out.println(isValidOp);

But for what validation of logical expressions will be necessary something more, as mentioned in the comments would have to ensure that for example the parentheses are closed when opened.

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