How can I use a Scala singleton object in Java?

Use Person$.MODULE$. See also

• How can I pass a Scala object reference around in Java?
• Singletons as Synthetic classes in Scala?

Edit: A working example (I checked, it compiles and works):
Scala:

object Person {
  val MALE = "m";
}

Java counterpart:

public class Test {
    Person$ myvar = Person$.MODULE$;

    public static void main(String argv[]) {
        System.out.println(new Test().myvar.MALE());
    }
}