If you don't want to use the line separator property ("\n"), you can try string format and use %n (works for Java 1.5 or above)
Example:
Calendar c = ...;
String s = String.format("Duke's Birthday: %1$tm %1$te,%1$tY%n", c); \
String s2 = String.format;
// %% becomes %
// and `%n` becomes a newline
Click here for more details.