If you are using Java 1.5 or later version, you can use STring.format(). You can use %n.
Calendar c = ...;
String s = String.format("Duke's Birthday: %1$tm %1$te,%1$tY%n", c);
//Note `%n` at end of line ^^
String s2 = String.format("Use %%n as a platform independent newline.%n");
// %% becomes % ^^
//