private PostfixCalculator convertToPostfix() {
        if (postfix == null || postfix.size() == 0 || isInfixChanged) {
            postfixCalculator.toPostfix(infix);
            postfix = postfixCalculator.getPostfix();
            isInfixChanged = false;
        }

        return postfixCalculator;
    }
private PostfixCalculator convertToPostfix ( ) { if ( postfix == null || postfix . size ( ) == 0 || isInfixChanged ) { postfixCalculator . toPostfix ( infix ) ; postfix = postfixCalculator . getPostfix ( ) ; isInfixChanged = false ; } return postfixCalculator ; }
Convert infix to postfix
Conversion is made only first time or after any change in structure of infix expression
@return