Left padding a String with Zeros [duplicate]

Answer 1

If you need performance and know the maximum size of the string use this:

String zeroPad = "0000000000000000";
String str0 = zeroPad.substring(str.length()) + str;

Be aware of the maximum string size. If it is bigger then the StringBuffer size, you'll get a java.lang.StringIndexOutOfBoundsException.