ContainsA

public class ContainsA {
  public static void check(String str) throws Exception {
    if (str.contains("a")) throw new Exception("Found \"a\".");
  }

  public static void main(String[] args) {
    try {
      check("ccc"); System.out.println("ccc is OK.");
      check("bbb"); System.out.println("bbb is OK.");
      check("aaa"); System.out.println("aaa is OK.");
    }
    catch (Exception e) {
      e.printStackTrace();
    }
  }
}