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.

Solution:

public class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<Character>();

        for (int i=0;i<s.length();i++){
            char cur = s.charAt(i);
            if (cur=='(' || cur=='[' || cur=='{')
                stack.push(cur);
            else {
                if (stack.isEmpty()) return false;
                char pre = stack.pop();
                if (!isMatch(pre,cur)) return false;
            }
        }

        if (!stack.isEmpty()) return false;
        else return true;
        
    }

    public boolean isMatch(char a, char b){
        if ((a=='(' && b==')') || (a=='[' && b==']') || (a=='{'&&b=='}')) 
            return true;
        else return false;
    }
}