leetcode--Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

public class Solution {
    public boolean isValid(String s) {
       boolean isValid = true;
        if(s.length() > 0){
            Stack<Character> parenStack = new Stack<Character>();
            for(int i = 0; i <s.length(); ++i){
                if(s.charAt(i) == '(' || s.charAt(i) == '[' || s.charAt(i) == '{')
                    parenStack.push(s.charAt(i));
                else{
                    if(s.charAt(i) == ')'){
                        if(parenStack.empty() || parenStack.peek() != '(')
                            isValid = false;
                        else
                            parenStack.pop();
                    }
                    if(s.charAt(i) == ']'){
                        if(parenStack.empty() || parenStack.peek() != '[')
                            isValid = false;
                        else
                            parenStack.pop();
                    }
                    if(s.charAt(i) == '}'){
                        if(parenStack.empty() || parenStack.peek() != '{')
                            isValid = false;
                        else
                            parenStack.pop();
                    }                    
                }
            }
            if(! parenStack.empty())
                isValid = false;
        }
        return isValid;
    }
}