What does the following statement sequence print? String str = "Java"; str += " is powerful"; System.out.println(str); O is powerful Java + is powerful Compile-time error O Java is powerful What does the following statement sequence print? String str = "Java Is Good"; int n = str.length(); String mystery = str.substring(n - 4, n) + str.charAt(4) + str.substring(0, 4); System.out.println(mystery); Good Is Good Good Java O Java