Is there any other way to remove all whitespaces in a string?

Question

I have a programming homework. It says that I need to reverse the string first, then change it to uppercase and then remove all the whitespaces. I actually did it, but our professor didn't say anything about using replaceAll() method. Is there any other way to do it beside replaceAll()?

Here is my code:

public static void main(String[] args) {
    String line = "the quick brown fox";
    String reverse = "";

    for (int i = line.length() - 1; i >= 0; i--) {
        reverse = reverse + line.charAt(i);
    }
    System.out.println(reverse.toUpperCase().replaceAll("\\s", ""));
}

Answer 1

You can check each character in turn using Character.isWhitespace. Additionally, it is generally better to use a StringBuilder when concatenating inside a loop.

public static void main(String[] args) {
    String line = "the quick brown fox";
    StringBuilder sb = new StringBuilder(line.length());

    for (int i = line.length() - 1; i >= 0; i--) {
        char c = line.charAt(i);
        if(!Character.isWhitespace(c)) sb.append(Character.toUpperCase(c));
    }
    System.out.println(sb);
}

Answer 2

@Khelwood's answer as code:

public static void main(String[] args) {
    String line = "the quick brown fox";
    String reverse = "";

    for (int i = line.length() - 1; i >= 0; i--) {
        char currentChar = line.charAt(i);
        if (currentChar != ' ') {
            reverse += currentChar;
        }
    }
    System.out.println(reverse.toUpperCase());

}