1106. Parsing A Boolean Expression

class Solution {
    public boolean parseBoolExpr(String expression) {
        Stack<Character> stack=new Stack<>();
        for(char c:expression.toCharArray()){
            switch(c) {
                case 't':
                case 'f':
                case '!':
                case '&':
                case '|':
                    stack.push(c);
                    break;
                case '(':
                case ',':
                    break;
                case ')':
                    evaluvate(stack);
                    break;
           }
        }
         while(stack.size()!=1){
                evaluvate(stack);
        }
         return  stack.peek()=='t'?true:false;
    }
    public void evaluvate( Stack<Character> stack){
        List<Boolean> ans=new ArrayList<>();
        char ch;
        do{
            ch=stack.pop();
            switch(ch) {
                case 't':
                    ans.add(Boolean.TRUE);
                    break;
                case 'f' :
                    ans.add(Boolean.FALSE);
                    break;
                case '|' :
                    boolean a=false;
                    for (Boolean b:ans){
                        a|=b;
                    }
                    stack.push(a==Boolean.TRUE?'t':'f');
                    break;
                case '&' :
                    boolean c=true;
                    for (boolean b:ans){
                        c&=b;
                    }
                    stack.push(c==Boolean.TRUE?'t':'f');
                    break;
                case '!' :
                    boolean d=ans.get(0);
                    stack.push(d==Boolean.TRUE?'f':'t');
                    break;
            }
            
        }while(ch!='!'&&ch!='|'&&ch!='&');
        
    }
        
}