Question

inttime[] is an array that already holds single-digit integer values. The first for loop seeks to convert each integer to a binary string and store it to the string array bintime[]. This part works fine, but when I try to run the next for loop, I get an illegal format conversion error.

for(int j = 0; j < inttime.length; j++){
bintime[j] = Integer.toBinaryString(inttime[j]);
}

for(int a = 0; a < bintime.length; a++){
System.out.println(String.format("%04d",bintime[a]));
}

Why is this happening if bintime[] is a String array?

Answer 1

If the bintime array holds Strings – as you’ve stated and you’re assigning to the array from Integer.toBinaryString – you’ll see an exception from format trying to print the String as int: the %d format expects an int, and not a String.

If you’re trying to pad the String representation of a base 2 number, then use something like:

System.out.println(
  String.format("%4s", Integer.toBinaryString(inttime[idx])).replace(' ', '0'));

The 4 in the format string represents the minimum width of the String, shorter strings will be padded with spaces.