Write a method to determine whether a character has a lowercase letter, and if so, it will be converted to uppercase letters, otherwise, not converted. three methods

public static void small(String a) {
	String aa[] = new String[a.length()];
	for (int i = 0; i < a.length(); i++) {
		aa[i] = a;
		if (!aa[i].toLowerCase().equals(aa[i])) {
			aa[i] = aa[i].toUpperCase();
		} else {
			System.out.println("不转换");
		}
	}
	String s = null;
	for (int i = 0; i < a.length(); i++) {
		s = aa[i];
	}
	System.out.println(s);

}

public static void small1(String line) {
	char[] arr = line.toCharArray();
	for (int i = 0; i < arr.length; i++) {
		char temp;
		if (arr[i] >= 97 && arr[i] <= 122) {
			arr[i] = (char) (arr[i] - 32);
		}
	}
	for (char a : arr) {
		System.out.print(a);
	}
}

public static char small2(char aChar) {
	if (Character.isLowerCase(aChar)) {
		return Character.toUpperCase(aChar);
	}
	return aChar;
}

 public static void main(String[] args) {
    small("aaBCDef");
	small1("aaBCDef");
	System.out.println();
	Scanner scanner = new Scanner(System.in);
	System.out.println("请输入一个字母");
	char aChar = scanner.nextLine().charAt(0);
	System.out.println(small2(aChar));
	}