不耻下问：Java语言字符串每5个一组，中间加上逗号，怎么用简单的办法实现呢

不耻下问：Java语言字符串每5个一组，中间加上逗号，怎么用简单的办法实现呢

public class test {

public static void main(String[] args) {
    //声明一个数组
    String[] str = new String[]{"1", "2", "3", "4"};
    //创建一个StringBuffer的对象
    StringBuffer str2 = new StringBuffer();
    //循环遍历数组
    for (int i = 0; i < str.length; i++) {
        //用append()方法拼接
        str2.append(str[i] + ",");
    }
    //用substring()方法截取掉最后一个 ","
    String str3 = str2.substring(0, str2.length() - 1);
    //输出拼接好的字符串
    System.out.println(str3 + "=================");
}

}

  public static void main(String[] args) {
    String str = "abcdefghijklmnopqrstuvwxyz";
    char[] chars = str.toCharArray();
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < chars.length; i++) {
      builder.append(chars[i]);
      if(i % 5 == 4){
        builder.append(",");
      }
    }
    System.out.println(builder.toString());
  }

    public static void main(String[] args) {
        String a = "aaaabbbbcccddddeee";
        StringBuffer buffer = new StringBuffer(a);
        // 计算插几个,
        int size = a.length() / 5;
        for (int i = 0; i < size; i++) {
            buffer.insert(5 * (i + 1) + i, ",");
        }
        System.out.println(buffer.toString());
    }

转成stringbuffer再来操作是最方便的