Java Data Type - 如何检查字符串是否平衡

import java.util.Stack;

public class Main {
  public static boolean isBalanced(String in) {
    Stack<Character> st = new Stack<Character>();

    for (char chr : in.toCharArray()) {
      switch (chr) {
      case '{':
      case '(':
      case '[':
        st.push(chr);
        break;
      case ']':
        if (st.isEmpty() || st.pop() != '[')
          return false;
        break;
      case ')':
        if (st.isEmpty() || st.pop() != '(')
          return false;
        break;
      case '}':
        if (st.isEmpty() || st.pop() != '{')
          return false;
        break;
      }
    }
    return st.isEmpty();
  }

  public static void main(String args[]) {
    System.out.println(isBalanced("level"));
    System.out.println(isBalanced("(level)"));
  }
}