Interfaces and implementation

Question

My first lecture in "Programming Distributed Components" included this code listing:
import java.util.Date;
import java.util.Comparator;
import java.io.*;
public interface LogMessage
public Date getDate();
public String getMessage();
public String getSource();
public Comparator BY_DATE_DESC = new Comparator()
public int compare(Object o1, Object o2)
LogMessage lhs = (LogMessage) o1;
LogMessage rhs = (LogMessage) o2;
int dateCompare = rhs.getDate().compareTo(lhs.getDate());
if(dateCompare == 0)//in the event that dates are equal sort by message
{                    //note - this is still a descending sort.
dateCompare = rhs.getMessage().compareTo(lhs.getMessage());
return dateCompare;
Call me stupid (please don't) but I was brought up to believe that java interfaces did not contain code implementation. Has the world gone mad or just my University lecturer? Or is it me? If the above code looks correct to you what is it that I am missing in my understanding of interfaces?
Thanks

Answer 1

I've not come across anything like this before. The
interfaces I have seen have tended to be rather simple
affairs consisting of simple contant declarations and
method signatures.They usually are. Your professor is getting fancy on you. Perhaps the point is to make you question what you think you know.
This opens up to me some other questions such as what
limitations are placed on the use of such objects? If
an object is a constant does that mean all its members
are constants? Why no use of "final" in this context -
is it already implicit in interfaces?There are no constants in Java per se. There are finals, which are variables that cannot be assigned once. A final primitve is effectively a constant and a final reference to an immutable Object (like a String) is effectively a constant (for our purposes.) All variables in interfaces are implicitly static and final.