Java: Filling a String up to a certain point

Question

I am working on a project but I am stuck at one point. I want the result string always to be 128 characters long. When my String is shorter, I want to replace it with "0"s. I tried many ways but none of them worked so I decided to ask it here.

This is something I have tried:

String s = "This is a String!";
if(s.length() < 128){
    s.replace(s.length(), 128, "0");
    System.out.println(s);
}

Answer 1

If you wanted your short String right-padded with zeros:

String s = "SomeTestString!";
if(s.length() < 128) {
   s = String.format("%-128s", s ).replace(' ', '0');
} else {
   s = s.substring(0,128);
}
System.out.println(s);

If you wanted your short String replaced with zeros:

String s = "SomeTestString!";
if(s.length() < 128) {
   s = s.replace(s.length(), 128, "0");
} else {
   s = s.substring(0,128) ;
}
System.out.println(s);

If you wanted short String to have 128 chars '0':

StringBuffer buf = new StringBuffer(128);
for (int i = 0; i < 128; i++) {
   buf.append("0");
}
System.out.println(buf);

Yeah, at least I practiced a bit :).