大写字符放在后，顺序不变，为啥必须加“***”

求助大佬们，StringBuffer不加“***“就导致输出为空  怎么解啊

import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
StringBuilder m1=new StringBuilder(sc.next());
//
test2(m1);

}


static void test2(StringBuilder m1){
for (int j =m1.length(); j >=0; j--) {
for (int i = 0; i <=j; i++) {
int n=i;
int m=i+1;
if(m>=m1.length()){break;}
if(m1.charAt(m)>=97&&m1.charAt(m)<123&&m1.charAt(n)>=65&&m1.charAt(n)<91){
String tem=m1.charAt(m)+"";
m1.replace(m, m+1, m1.charAt(n)+"");
m1.replace(n, n+1, tem);
}
}}

String ss=new String(m1);
System.out.print(ss+"***");
//System.out.println(ss);
/*char[] cs = ss.toCharArray();
for (int i = 0; i < cs.length; i++) {
System.out.print(cs[i]);
}*/

}

}