1106. Parsing a boolean expression

//1106. Parsing a boolean expression

public class Solution {

    public boolean parseBoolExpr(String expression) {
        Stack<Character> st = new Stack<>();

        for(char currChar : expression.toCharArray()) {
            if(currChar == ',' || currChar == '(') {
              continue;
            }

            if(
                currChar == 't' ||
                currChar == 'f' ||
                currChar == '!' ||
                currChar == '&' ||
                currChar == '|'
            ) {
                st.push(currChar);
            }
            else if(currChar == ')') {
                boolean hasTrue = false, hasFalse = false;

                while(st.peek() != '!' && st.peek() != '&' && st.peek() != '|') {
                    char topValue = st.pop();

                    if(topValue == 't') {
                      hasTrue = true;
                    }

                    if(topValue == 'f') {
                      hasFalse = true;
                    }
                }

                char op = st.pop();

                if(op == '!') {
                    st.push(hasTrue ? 'f' : 't');
                }
                else if(op == '&') {
                    st.push(hasFalse ? 'f' : 't');
                }
                else {
                    st.push(hasTrue ? 't' : 'f');
                }
            }
        }

        return st.peek() == 't';
    }
}