This won't compile.
Did you mean
System.out.printf("12%1$s", "13%1$s", "14%1$s");?
This will print
1213%1$s.
The format
string is
12%1$s.
12%1$s: this part just prints 12. Nothing special about it.
12%1$s: this part prints a parameter with index 1 as a String, which is
13%1$s.
Read
this for more info.