Java Data Type - 如何将字符串拆分为大写字母的字符

public class Main {
  public static void main(String[] args) {
    String input = "ThisIsATest";

    // split into words
    String[] words = input.split("(?=[A-Z])");

    words[0] = capitalizeFirstLetter(words[0]);

    // join
    StringBuilder builder = new StringBuilder();
    for (String s : words) {
      builder.append(s).append(" ");
    }

    System.out.println(builder.toString());

  }

  private static String capitalizeFirstLetter(String in) {
    return in.substring(0, 1).toUpperCase() + in.substring(1);
  }
}