Java最简单的字符串4位加一个空格

String string="0123456789abcd";StringBuilder str = new StringBuilder(string.replace(" ",""));    int i = str.length() / 4;    int j = str.length() % 4;    for (int x = (j == 0 ? i - 1 : i); x > 0; x--) {        str = str.insert(x * 4," ");    }System.out.println(str);