Why is String.Format("%1s","") not returning "" but " "?

Question

String.format("%1s","").equals("")); // --> return false !
String.format("%1s","").equals(" ")); // --> return true !

• Why is this happening ?
• Where does the space come from ?

Answer 1

The space is specified by the minimum width value 1 in the format specifier

String.format("%1s","").equals(" ")
                ^

Answer 2

You wanted to add an argument index like this

String.format("%1$s", ""); //returns ""
String.format("%2$s %1$s", "a", "b"); //returns "b a"

Your code defined a "width"

String.format("%3s", ""); // returns "   ";
String.format("%3s", "a"); // returns "  a";
String.format("%-3s", "a"); // returns "a  ";

Read this for more info: http://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html#syntax