How to convert string array to comma separated string in Java

public static void main(String[] args) {
    String strs = "";
    String[] arr = new String[]{"aa", "cc", "bb"}; // 转换前的字符串数组
    StringBuilder sb = new StringBuilder();
    for (String ele : arr) {
      if (sb.length() > 0) {
        sb.append(",");
      }
      sb.append(ele);
    }
    strs = sb.toString(); // 转换后的逗号分隔字符串
    System.out.println(strs);
}

public static void main(String[] args) {
    String[] arr = new String[]{"aa", "cc", "bb"}; // 转换前的字符串数组
    String strs = String.join(",", arr); // 转换后的逗号分隔字符串
    System.out.println(strs);
}