leetcode[20] Valid Parentheses

class Solution {
    public boolean isValid(String s) {

        Stack<Character> stack = new Stack<Character>();

        if(null != s && s.length() > 0){
            
            char[] charArray = s.toCharArray();
    
            for(char c : charArray){

            if(c == '('){
                stack.addElement(')');
            }else if(c == '{'){
                stack.addElement('}');
            }else if(c == '['){
                stack.addElement(']');
            }else if(stack.isEmpty() || stack.pop() != c){
                return false;
            }

        }
            
        }
        
        return stack.isEmpty();
    }
}