leetcode-java-20. Valid Parentheses

public class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<Character>();
stack.push(s.charAt(0));

int len = s.length(),
i = 1;

for(;i < len;i++) {
if(!stack.empty() && isMatch(stack.peek(),s.charAt(i))) {
stack.pop();
} else {
stack.push(s.charAt(i));
}
}

if(stack.empty()) {
return true;
} else {
return false;
}
}

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