Java balanced expressions check {[()]}

Question

I am trying to create a program that takes a string as an argument into its constructor. I need a method that checks whether the string is a balanced parenthesized expressio

Answer 1

The improved method, from @Smartoop.

public boolean balancedParenthensies(String str) {
    List leftKeys = Arrays.asList('{', '(', '<', '[');
    List rightKeys = Arrays.asList('}', ')', '>', ']');

    Stack stack = new Stack<>();
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        if (leftKeys.contains(c)) {
            stack.push(c);
        } else if (rightKeys.contains(c)) {
            int index = rightKeys.indexOf(c);
            if (stack.isEmpty() || stack.pop() != leftKeys.get(index)) {
                return false;
            }
        }
    }
    return stack.isEmpty();
}