Validate String parathesis

Simple program to validate parenthesis in a string. e.g. "(12(ab(dkc)))" is valid but "(12(ab)(dkc)))" is not

The simple solution is to use stack to push the "(" character and pop the same when you have ")"

import java.util.Stack;

public class StringValidation {

public Boolean isValid(String str) {

Boolean isValid = true;

Stack stack = new Stack<>();

char[] chars = str.toCharArray();

for (char achar : chars) {

if (achar == '(') {

stack.push(achar);

}

if (achar == ')') {

if (stack.isEmpty()) return false;

stack.pop();

}

}

if (!stack.isEmpty()) return false;

return isValid;

}

public static void main(String [] args) {

String str1 = "(12(ab(dkc)))";

                String str2 = "(12(a)b(dkc)))";

StringValidation ex = new StringValidation();

System.out.println("str1: " + ex.isValid(str1));

                System.out.println("str2: " + ex.isValid(str2));

}

}