Interfaces instead of multiple inheritance?

Question

I've read that "The Java programming language does not permit multiple inheritance , but interfaces provide an alternative."
But I also read contradictory information-There are no method bodies in an interface.
Java interfaces only contain empty methods? Apparently, if I want to share a method among classes, I have to re-write the methods in each class that implements the interface. That doesn't seem at all like multiple inheritance. Am I missing something?
It seems that I will have to cut and paste the implementation code from one class to another, and if I change the methods, I have to cut and paste it all over again.
I've read that interfaces save a lot of time re-writing methods, but how?
Does this really provide the same capabilities as multiple inheritance, or am I missing something?
Thanks,
Pat

Answer 1

Pat-2112 wrote:
I've read that "The Java programming language does not permit multiple inheritance , but interfaces provide an alternative."
But I also read contradictory information-There are no method bodies in an interface. That's not contradictory.
Inheritance is about type, which interfaces provide. It is NOT about sharing code, which is all that's lacking by not having multiple inheritance of implementation.
Java interfaces only contain empty methods? Apparently, if I want to share a method among classes, I have to re-write the methods in each class that implements the interface. That doesn't seem at all like multiple inheritance. Am I missing something? Yup. You're missing the point of inheritance, and the fact that delegation allows you to use an implementation defined in one class in another class.
It seems that I will have to cut and paste the implementation code from one class to another, Nope.
public interface Cowboy {
  void ride();
  void draw();
public interface Artist {
  void sculpt();
  void draw();
public interface CowboyArtist extends Cowboy, Artist {
public class CowboyImpl implements Cowboy {
  public void ride() {
   System.out.println("Giddyup!");
  public void draw() {
    S.o.p("Bang!");
public class ArtistImpl implements Artist {
  public void sculpt() {
    S.o.p("Demi Moore in Ghost. Yum!");
  public void draw() {
    S.o.p("Sketch a picture of a gun.");
public class CowboyArtistImpl implements CowboyArtist { // or implements Cowboy, Artist
  private final Cowboy cowboy = new CowboyImpl();
  private final Artist artist = new AristImpl();
  public void ride() {
    cowboy.ride();
  public void sculpt() {
    artist.sculpt();
  public void draw() { // uh-oh, what do we do here?
    artist.draw();
    cowboy.draw();
}The draw method is not relevant to this particular question. It's an example of one of the problems with MI, and I just included it since it usually comes up int these discussions anyway. Ride and sculpt demonstrate the point about delegation.