写个函数func(str)，传参str为一个字符串次序逆序。比如把 I am a coder变成 coder a am I，不允许使用正则，reverse，join，substr，split，find

    String s = " I am a coder ";
    String str = "";
    String s1 = "";
    for (int i = 0; i < s.length(); i++) {
        String data = String.valueOf(s.charAt(i));
        if (!" ".equals(data)) {
            str += data;
                continue;
        }
        if (!"".equals(str)) {
            s1= str+" "+s1;
            str = "";
        }
    }
    System.out.println(s1.trim());