Compile-time warning during javac of a Class that implements Comparable

Question

Hello All,
I have defined a class as follows;
public class CardTiles extends JButton implements Comparable{
During normal compilation with javac, it tell me to use Xlint to compile and the warning it throws is below:
CardTiles.java:4: warning: [serial] serializable class CardTiles has no definition of serialVersionUID
public class CardTiles extends JButton implements Comparable{
^
1 warning
What does this warning mean?
Many thanks!

Answer 1

ejp wrote:
you can choose to to differentiate between various versions of your CardTiles classThat's back to front. Serialization will always do that unless you stop it, which you can do via a fixed serialVersionUID. This tells Serialization that different versions of your class are compatible under serialization.I suppose I see it this way because I wouldn't have a serializable object without an ID. Without having an explicit ID the process isn't as transparent to me. It's the same sort of thing as using braces for statements when they're not necessary, e.g.
          if(check)
               System.out.println("check is on");
          else
               System.out.println("check is off");     versus     
          if(check) {
               System.out.println("check is on");
          } else {
               System.out.println("check is off");
          }