Multiple inheritance in tagging interface? Is it possible?

I saw a code somewhere that goes like this:
public interface Node extends Serializable, Clonable
...Is it possible? I know that Java doesn't allow multiple inheritance and that Serializable and Clonable are tagging interfaces where no method must be implemented by the programmer.

KamenRiderZX wrote:
I know that Java doesn't allow multiple inheritanceMore exactly: Java doesn't allow multiple inheritance of implementations. Inheriting multiple interfaces ("implements" for classes, "extends" for interfaces) is fine 'though.

Similar Messages

Multiple inheritance in remote interfaces for EJB 3.0 session beans on Webl

Hi All,
We started migration from EJB 2.1(WLS 8.1) to EJB 3.0(WLS 10.3.2) and identified few serious problems. One of them is related with multiple business interfaces inheritance. I wrote simple example that presents point of the problem.
we have session bean AImpl:
+@Stateless(name="A")+
+@Remote({A.class})+
+@TransactionAttribute(TransactionAttributeType.REQUIRED)+
+public class AImpl implements A {+
+@Override+
+public void writeA() {+
System.out.println("A");
+}+
+@Override+
+public void writeB() {+
System.out.println("B");
+}+
+@Override+
+public void writeC() {+
System.out.println("C");
+}+
+}+
with remote interface A:
+@Remote+
+@JNDIName(A.JNDI_NAME)+
+public interface A extends B, C {+
public static String JNDI_NAME = "A_JNDI_NAME";
void writeA();
+}+
As you can see A extends B, and C. Definition of both interfaces is very simple:
+public interface B {+
void writeB();
+}+
+public interface C {+
void writeC();
+}+
Everything looks nice until we want to invoke some method on AImpl bean. For above implementation code:
A a = ctx.lookup(A. JNDI_NAME);
a.writeA();
a.writeB();
a.writeC();
writes down ”A \n B” and throws exception:
caused by: java.lang.NoSuchMethodException: pl.gov.arimr.zszik.bazowe.slowniki.ejb.A_vt0zts_AImpl_1032_WLStub.*writeC()*
at java.lang.Class.getMethod(Class.java:1605)
at weblogic.ejb.container.internal.RemoteBusinessIntfProxy.getTargetMethod(RemoteBusinessIntfProxy.java:165)
at weblogic.ejb.container.internal.RemoteBusinessIntfProxy.invoke(RemoteBusinessIntfProxy.java:57)
so.. in stub generated by WLS there is no method from interface C ! What more interesting after small change in interface A rely on change in interface implementation order from B, C to C, B (+public interface A extends C, B {+) server writes down only A and I have stack like below:
Caused by: java.lang.NoSuchMethodException: pl.gov.arimr.zszik.bazowe.slowniki.ejb.A_vt0zts_AImpl_1032_WLStub.*writeB()*
at java.lang.Class.getMethod(Class.java:1605)
at weblogic.ejb.container.internal.RemoteBusinessIntfProxy.getTargetMethod(RemoteBusinessIntfProxy.java:165)
at weblogic.ejb.container.internal.RemoteBusinessIntfProxy.invoke(RemoteBusinessIntfProxy.java:57)
After this experience I came up with suspicion that Weblogic 10.3 does not support inheritance from multiple interfaces in one “generation”. Instead of that it takes only the first interface from the list.
Does anybody have some experience with such a situation? maybe someone have an idea how to work around this problem?

This is Not Supported in WebLogic that the Remote Interface extends other Interfaces. Because Annotation Processor just looks up inside the implemented interface methods. The actual interface which is Implemented by the Bean Class. So the Methods declared inside the Interface B and Interface C will be ignored and will not be available as part of the generated Stubs. Thats why u are getting NoSuchMethodError.
You can even contact Oracle Support on this...there are 3-4 Cases on it. And the Solution is Work As Designed.
Workaround is : edit your interface A as following
Declare all the Business Methods only in the Remote Interface and not inside it's Super Interfaces.
Example:
@Stateless(name="A")
@Remote({A.class})
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public class AImpl implements A {
@Override
public void writeA() {
System.out.println("A");
@Override
public void writeB() {
System.out.println("B");
@Override
public void writeC() {
System.out.println("C");
@Remote
@JNDIName(A.JNDI_NAME)
public interface A extends B, C {
public static String JNDI_NAME = "A_JNDI_NAME";
void writeA();
void writeB();
void writeC();
Thanks
Jay SenSharma
http://jaysensharma.wordpress.com (WebLogic Wonders Are Here)

Doubt on Multiple Inheritance

Hi all,
I am confused by the java statement that "By using interface we can achieve multiple inheritance bcoz java doesn't support Multiple inheritance".
Yes.Ok java doent support Multiple inheritance. Now we know that inheritance means that "one object acquires the property of another object".
So how can it is possible achieve Multiple inheritance by interface.
Interface that contains just undefined methods like below code.
interface Member1
     public void eye();
     public void nose();
     public void mouth();
interface Member2 extends member1
     public void neck();
     public void hand();
     public void stomach();
interface Member3 extends Member1,Member2
     public void leg();
class Man implements Member3
     public man()
     Member3 ref=new Man();
     // Here Implements all 7 methods.
Is the above code defines multiple Inheitance?
undefined methods are eye,nose,mouth,neck,handand stomach are fall in Interface Member3 .Yes. But Inheritance means that one object acquires the property of another object.Property means that code and data.
In here, there is no code just declarations of method which is not to be a code .
So How can we say interface achieve multiple inheritance.
Please any one explain and clear my doubt with simple example.
with cheers,
G.GandhiRaj.

Multiple inheritance is about aquiring both behavior and attributes from two or more sources. A lot of times, this "is a" relationship is confused with "has a" relationships.
For example, a Book "has a" Page. A Book "is a" Publication. So multiple inheretance in this instance would come from stating that a Book "is a" Publication and "is a" PaperProduct. In this example, you could redesign your model and state that a PaperProduct inherits from Publication. However, a Book doesn't have to be limited to being a PaperProduct, it can also be an ElectronicProduct, thus inhereting attributes and behaviors from this new class as well. In essence, the Book can exist in two forms simulataneously (as many actually do). So you still have the need for multiple inheritance - perhaps.
Interfaces define the behavioral aspects of multiple inheritance. You loose the aquisition of attributes from base classes. In many cases this is acceptable. For the first time I recently found a true need for multiple inheritance in one fo my Java apps. Some would say that my data model is poorly designed then. So I tried restructuring the model and that solve the problem.
It is probably a good idea to completely understand your data model from many dimensions first before resorting to the copying of attributes like I almost did. Don't be locked into a design too quickly. Be willing to change your mind and you will probably find a solution that works.

How does Java achieve multiple inheritance using interfaces

Java does not allow multiple inheritance through classes as classes might contain methods with same names. what happens if a class implements two interfaces with same method names?
I am really confused abt this? Can anybody help me out?
Message was edited by:
vijkris

yes to avoid the ambiguous functions which can result due to multiple inheritance of classes like in c++ , java doesn't have this through classes. But if you have same method (both return type and parameter) then java doesn't bother and it won't complain as ultimately only one implementation is possible in deriving class even though method declalaration is there in both the interfaces. If return type changes then it won't compile as it can't overide the both methods as they have same name and different return types. thats why inside interfaces they restricted the implementation of methods so that it can work fine in ambiguous scenarios.

How java support multiple inheritance by the use of interface.

As per my understanding, Interface is just having the signatures of the methods not the implementation.
So How java support multiple inheritance by the use of interface?
Answer 1: we can institate interface reference by its implemented
class.
          �� interface inf...
          �� class aa implements inf..
          �� class bb implements inf....
           Now, inf i = new aa();
           inf i = new bb();
Answer 2: We can extends as many interface as we want in the
single
           interface.
           i.e. interface infFirst....
           interface infSecond....
           interface infThird....
           Now ,
           interface ingMulti extends infFrist, infThird...
By above two answers its not prity clear as per the multiple inheritance in C or C++.
           i.e.
           class first{
           method abc();....}
           class second{
           method bbc()......}
           class multi::first::second{
           we can call to abc();.....as well as bbc();
-Please give your important suggstion on the same.(Hope I explain it well.)
-Jeff

The keyword implement is used only for interfaces not
for abstract class. If i am wrong correct me.I believe your right, but I will double check.
As for the multiple inheritence think about the following code:
class Animal {
    // Animal generic stuff in this class
interface Eat {
    // Generic stuff that models eating behavior
interface Runs {
    // generic methods that model running behavior
public class Horse extends Animal implements Eat, Runs {
    // Stuff specific to a horse
}The Animal class is generic but has stuff in it common to all animals.
The Eat interface models behavior that is generic to eating, all living things have to eat something to survive. Herbavore are different from carnivores.
The Runs interface models generic behavior to running, such as speed. A cheeta definately runs faster than a human.
This brings us to the Horse class. It extends the Animal class because it "is-a" animal, and it implements the eat and runs interface because they are behaviors a horse has.
I hope that helps.
Extending an abstract class is the same as extending a regular class with the exception you MUST override all abstract methods in the abstract class. Thats not too difficult but I believe when designing classes, designing an abstract can be more diffecult than modeling the base class, and generic behaviors in interfaces. JMO.
JJ

No multiple inheritance in Java. Interfaces used.

Hi,
In java a class can extend only one class while the interface can extend any number of interfaces.
Class extending only one class avoids multiple inheritance.
Can you explain me the reason of avoiding this in classes and allowing interfaces to extend any number of interfaces ?

Hi,
In java a class can extend only one class while the
interface can extend any number of interfaces.
Class extending only one class avoids multiple
inheritance.
Can you explain me the reason of avoiding this in
classes and allowing interfaces to extend any number
of interfaces ?The real question is: do you have a need for multiple inheritance?
If so, I would be glad to hear about this concrete problem.

Multiple Inheritance problem persists in Interfaces

Hi,
I tentatively made a program and found that multiple inheritance problem of C++ persists even with interfaces. Although this is definetely a special case but I want to know what is this problem known as( i know that this is perhaps known as diamond problem in C++). And is there a way out of this thing.
interface one
     int i=10;
interface two
     int i=20;
interface z extends one,two
public class xyz implements z
     public static void main(String [] a)
     System.out.println(i);
}O/P
D:\Education\Java\JavaStudyRoom\Applets>javac xyz.java
xyz.java:16: reference to i is ambiguous, both variable i in one and variable i
in two match
System.out.println(i);
*^*
*1 error*
Thanks for replying

suvojit168 wrote:
I tentatively made a program and found that multiple inheritance problem of C++ persists even with interfaces. Although this is definetely a special case but I want to know what is this problem known as( i know that this is perhaps known as diamond problem in C++). And is there a way out of this thing. This is not the so called diamond inheritance problem. What you have here is an ordinary name clash. And as has been noted you can resolve it by qualifying which constant you're referring to, like
System.out.println(one.i);
For the diamond inheritance problem to apply both the one and the two interfaces would need to inherit a common ancestor (that's how the diamond is formed). Furthermore the common anscestor would need to carry implementation which would then be inherited two ways, once via one and once via two. This is the diamond inheritance problem Java is avoiding by allowing single inheritance of implementation only.
P.S. My previous post was posted my mistake.

How too ? Multiple inheritance with Interface ?

I understand that Java does NOT allow Multiple inheritance. I've read many posts trying to understand the interface statement.
I understand that an interface implements a behavior! But can someone please explain how I would inherit Multiple classes (Thread and JPanel) using an interface ?
Many Thanks,
Rob

I understand that an interface implements a behavior!No, it doesn't. It merely defines what methods must be present in a type. A class is what actually implements the behavior for a particular implementation of that type.
But can someone please explain how I would inherit
Multiple classes (Thread and JPanel) using an
interface ?You can't. Thread and JPanel are classes. A given class can only extend one class.
A class can implement multiple interfaces however. So if at least one of Thread or JPanel were an interface, then your class could inherit from both of them. But that's not the case, so you can't.

Interfaces instead of multiple inheritance?

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

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.

Multiple Inheritance

Hello,
I have been programming Java for last year,
evolved in quite some skills with it, and
really think it is great...
However, I was shocked to find out that there
is no multiple inheritance feature.
I know it is rare, and my case proves it
(1 year now, I never needed it)
HOWEVER, when one needs multiple inheritance,
then they really do need it.
I have interfaces which I would like implemented
in their respective class (ie ISomething be
implemented in CSomething), then some classes
I need to implement many of those interfaces...
Now I am forced to have those classes extend
multiple interfaces, and duplicate the interface
implementation code inside each of them.
I dont mind a little bit of copy/paste, nor
do I care about the compiled classes being
slightly bigger, BUT the problem is that
when I need to change some behaviour in those
interfaces, in the near (or far) future, I will
have their implementation scattered in many
classes... This is dangerously error prone and
not proffesional at all... And I do not think
that including multiple inheritance in the language
could be more error prone than this...
I think the Java team does a 100% perfect brilliant
job, but at this specific point, they "over-tried"
to "protect" the programmers from themselves...
Well, thats all,
I think some next version of Java should support
multiple inheritance. And the Java "warning" could be :
"if you havent missed it till now, then you probably
do not need anyway, so do not bother using it just
because it exists"
Thanks for reading my thoughts,
Dimitris

Personally I never need multiple inheritance of code and I try to avoid inheritance of code whenever possible. A common mistake in OO is too use inheritance as a way of reusing code. Code reuse is much easier, cleaner and more powerful by using composition instead. Only use inheritance for polymorhism (to use multiple implementations for the same interface). An example:
interface A {
void ma();
void maa();
interface B {
void mb();
class C implements A, B {
private A a;
private A c;
private B b;
public void ma() {
    a.ma();
public void maa() {
    c.maa();
public void mb() {
    b.mb();
}This is much more powerful than code reuse through inheritance. In this example I use one method from 'a' and one method from 'c' when I implement interface A. I can change the value of 'a', 'b' and 'c' during runtime, and I dont have to reuse all the code in 'a' and 'b', I can select which code to reuse. This is the power of composition and interfaces. Note that I only access 'a', 'b' and 'c' through the interfaces A and B, never directly through their implementations.
I would recommend you to look at your design and start to think about interfaces and inheritance, not about code reuse though inheritance.

Enumerate multiple inheritance scenarios and their java equivalents?

hi,
ppl have often said things like
"java doesn't support multiple inheritance but this is ok, since there are other mechanisms for doing the same thing (by which we nearly always mean interfaces)"
how solid a statement is this? are there any formal methods available eg smt like "over all possible inheritance trees over all possible classes, only a handful of cases are distinct when viewed from the converting-to-single-inheritance scheme"?
the two things mentioned as harder to workaround are mixins and the diamond problem - are there more?
also what other mechanism apart from interfaces (if any) are useful?
any help appreciated,
asjf

What I say is that it doesn't matter since there is
almost never any need for MI. Most of the time it is
used it is used because the developer/designer did not
understand what they were doing and it should not have
been used in the first place.
That leaves one with very few cases where it should
ever be used. And that coupled with the fact that a
developer should never use it unless they are very
experienced (so that they actually know that it should
be used,) means that practicing programmers should
leave discussion of such usages to scholarly
journals.thanks :) I guess my problem is that often with computer stuff you don't have to rely on other peoples experience about things - you can go and test it yourself
I've done very little C++ development, and so have never come across real-world multiple inheritance. I bumped into the first situation with some java code where it might've been a neat solution recently but this could easily fit into the "designer did not understand what they were doing" category from above..
will have a casual look around the scholarly journals if I can find any that look promising :)
asjf

Hi All , Will Java supports Multiple Inheritance classes???

Hi All ,
Will Java supports Multiple Inheritance by classes???
Thanks in advance,
Prakash

No, Multiple inheritance would look like
public class A extends B,C {(You can do that in C++, but it's rarely a good idea).That's not true at all. It's not inherently harmful, in C++ or any other language. It's entirely possible to do it correctly when it truly makes sense.
Java just guarantees that nothing bad can happen to you by only allowing multiple inheritance of interface. You can't ever have multiple inheritance of implementation, that's all.
%

Multiple-inheritance semantics

I saw the other day multiple-inheritance is possible with JavaFX classes.
class X extends Y,Z,A {
Something which is possible now as JavaFX classes don't have constructors. Now we can mix-in (as in Scala) code from other classes.
My question to the people who design this is about their intention: is it meant to be used as a composition ? Or still as a specialization like it is in Java.

If you allow multiple inheritance you get some ambiguities. Java avoid those by having single inheritance of implementation (one class may extend one class only) in addition to multiple inheritance of interfaces (that don't implement anything). This is much cleaner and that was one of Javas design objectives. The goal is to be safer than C++ and this often means leaving things out, like calls by reference, pointer arithmetics and multiple inheritance.

More about multiple inheritance

OK, you can solve problems where multiple inheritance is needed by using interfaces. But im facing a problem where it cant help me. Im constructing a system where there are componentes that need to extend JTextField as well Observable. I dont have interfaces above it in the hierarchy to substitute multiple inheritance. What can I do?
When you have a scenario that you have to use two (or more) third party classes, and need to inherit from both, how do interfaces can help? If ate least I had multiple inheritance from classes...

<< Begin Rant >>
I have seen more inherited code that is terribly designed because multiple inheritence was available.
The example provided is a perfect example of this: At first blush, it seems easy to combine the UI and data components by combining Observable and JTextArea. If you were able to do this, the person inheriting your code in 3 years will curse your name.
Nothing pisses me off more (well, I'm sure there are other things, but...) than attempting to debug C++ source code and finding that function calls are being made to multiple super classes.
Here's a fun one: try adding an innocuous method getInfo() to a class you've inherited, only to find that someone uses getInfo() in one of the super-classes, and it has been declared as 'friend' because the design is piss poor and it was the only way they could make the function available. Now, I have to go on a goose chase searching for all the places in the entire type hierarchy that getInfo() is used and change the code to explicitly call the other base class.
It gets to the point where its easier to name it getInfo2() (like that's good design) and get on with things.
MI is evil, evil, evil in any environment where you are trying to have code re-use and multiple teams.
I find that most programmers who insist that multiple inheritence is a good thing just don't know how to use the Composite design pattern.
Sun's decision to not support MI in Java is a sound one: the result is code that can be easily read and understood.
<< End Rant >>
Whew... I feel much better having said that...
- K

Problems of no multiple inheritance.

I have created two classes RECTANGLE with attributes Length and Height and PLANERECTANGLE, with various attributes required to specify the rectangle's center, an attribute that can be checked to see if it is inside an instance of rectangele. However, i am finding this following requirement difficult to understand.
In Question 5, we specified PlaneRectangle as a subclass of Rectangle. Suppose that we wanted the following generic behaviour to be implemented in a number of different �kinds of� shapes: being able to move a shape, check if a point is inside a shape, and check if another shape lies completely inside a specified instance of some shape. Java will not let us do this using multiple inheritance. How else could we specify this? Rewrite the Java code to illustrate use of this different method.
Thanks - Mark Costello.

The answer would be an interface
public interface Shape
public void moveShape();
public boolean containsPoint(int x, int y);
public boolean containsShape(Shape s);
Every shape class would then implement this interface:
public class Circle implements Shape
... and would need to implement those methods that
were specified (but not implemented) in the interface.

Multiple inheritance in tagging interface? Is it possible?

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