W3School TIY Editor

public class Main {

  public static void main(String[] args) {

    String originalStr = "Hello";

    String reversedStr = "";

    System.out.println("原始字符串: " + originalStr);

    for (int i = 0; i < originalStr.length(); i++) {

      reversedStr = originalStr.charAt(i) + reversedStr;

    }

    System.out.println("反转后字符串: "+ reversedStr);

  }

}