You can leave the initial statement blank and just put a semicolon.
for(; start <= end; start++)
Just do:
for(int i = start; i <= end; i++){
end--;
System.out.print(start);
}
Although in actuality if you want your code to work you have to do:
for(int i = start; i <= end; i++){
System.out.print(start);
}