This is a method to display a character string formatted with a numerical value such as double.
String.format("%1$,.0f" + "In KB," + "%2$,.0f"+ "KB processed." + "%3$,.0f" + " %%Processing completed",
a / 1024.0, b / 1024.0, c / 1024.0);
The placeholders inside are
%1$ -> a / 1024.0
%2$ -> b / 1024.0
%3$ -> c / 1024.0
Corresponds to variable length arguments. further
,.0f
So, it means "separated by commas with 3 digits" and "0 digits after the decimal point".
By the way, when using% in the format, escape by %% as above. ..