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.

Similar Messages

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.

Multiple Inheritance of Class problem

I want to inherit two classes in my class
Since java does not support multiple inheritance of java classes , only can implement java interface , how can I achieve this .

I too have a dream.
Someday I want to see a design that uses multiple inheritance correctly. And as long as I am dreaming it might as well be a design that is not dependent on legacy applications.
I strongly suspect that it will forever remain a dream.

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

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.

INF Looking for means to dialog C#-Dev team about multiple inheritance.

Please help.
I really need multiple inheritance with C#. Is there any forum/means to have a dialog with the dev's for C# about this? The amount of extra work and maintenance costs of not having multiple inheritance has been a big problem, but lately, it has really become
a burden for not having. The maintainability and reuse-ability of code is drastically reduced without it.

Btw, I think that this has been discussed
many times before. Almost once or twice each year since .NET is released (that's 12 years by now).
I don't think you can make them allow this feature as tons of example trying to convince them this is needed has been proved not necessary to use multiple inheritance by them.
Many of the discussions ends with something like "Java also does not support multiple inheritance but there isn't seems to be a problem for them". Maybe you can get more luck to convince Oracle to include MI in Java first.
Btw, I found it hard to believe you need Multiple Implementation Inheritance to... improve maintainability of code? WTF??? I think Multiple Implementation Inheritance has it own place in the hall of fame for the bugs it caused in languages that supports
it, even in C++.

Alternatives to multiple inheritance for my architecture (NPCs in a Realtime Strategy game)?

Coding isn't that hard actually. The hard part is to write code that makes sense, is readable and understandable. So I want to get a better developer and create some solid architecture.
So I want to do create an architecture for NPCs in a video-game. It is a Realtime
Strategy game like Starcraft, Age of Empires, Command & Conquers, etc etc.. So I'll have different kinds of NPCs. A NPC can have one to many abilities (methods) of these: Build(), Farm() and Attack().
Examples:
Worker can Build() and Farm()
Warrior can Attack()
Citizen can Build(), Farm() and Attack()
Fisherman can Farm() and Attack()
I hope everything is clear so far.
So now I do have my NPC Types and their abilities. But lets come to the technical / programmatical aspect.
What would be a good programmatic architecture for my different kinds of NPCs?
Okay I could have a base class. Actually I think this is a good way to stick with the DRY principle.
So I can have methods like WalkTo(x,y) in
my base class since every NPC will be able to move. But now lets come to the real problem. Where do I implement my abilities? (remember: Build(), Farm() and Attack())
Since the abilities will consists of the same logic it would be annoying / break DRY principle to implement them for each NPC (Worker,Warrior, ..).
Okay I could implement the abilities within the base class. This would require some kind of logic that verifies if a NPC can use ability X. IsBuilder, CanBuild,
.. I think it is clear what I want to express.
But I don't feel very well with this idea. This sounds like a bloated base class with too much functionality.
I do use C# as programming language. So multiple inheritance isn't an opinion here. Means: Having extra base classes like Fisherman
: Farmer, Attacker won't work.

Hi
PandoraElite，
You can inherit from multiple interfaces (and use explicit interface implementation), but not from classes in C#. You can almost simulate it:
In C# we don't support multiple inheritance
http://blogs.msdn.com/b/csharpfaq/archive/2004/03/07/why-doesn-t-c-support-multiple-inheritance.aspx
What would be a good programmatic architecture for my different kinds of NPCs?
In your scenario, we can define some interface ,An interface contains only the signatures of methods, properties, events or indexers. A class or struct that implements the interface must implement the members of the interface that are specified
in the interface definition.
How to use? Please refer to the following article.
http://www.codeproject.com/Articles/18743/Interfaces-in-C-For-Beginners
Best of luck!
Kristin
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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.

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

Replacement for multiple inheritance in MovieClip class

Hello
I need your opinion about a problem.
Commonly, when you need to replace multiple inheritance, you do it by making an aggregation with one of the class involved.
But in case of MovieClip attached class, there is one more class involved in the process : the MovieClip class, and this class can't be the one aggregated because every class attached to a MovieClip need to inherits from it.
The problem is if the other class can't be also aggregated because it has some abstract class behaviour, for instance, call of a virtual function.
A solution could be making the abstract class inherit from the MovieClip class, but what if you want to reuse its behaviour in a class which have nothing to do with MovieClip ?

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)

Multiple inheritance, delegation and syntactic sugar

Given that delegation of an interface to a class member gives you most of the effect of multiple inheritance, why isn't there any syntactic sugar in the language to make this easy?
For example, you could have:
class B extends A implements I delegate i { I i = new IAdapter(); }
The semantics is simple: for each method in each delegated interface, if there is no method with that signature defined in the class then create one with a body that delegates the call to the given member. If there is an ambiguity from multiple interfaces, just flag it at compile time so that the programmer must add an explicit method.
This doesn't impact the class file format as it isn't doing anything that can't be done longhand in the code. It would even provide some protection from interface changes, as a recompile would pass the problem on to the delegate (which would likely inherit from some standard adapter class which would be modified at the same time as the interface).
Why isn't this done (apart from because MI is inherently evil and just suggesting this addition means I'm a bad person). It would make the language a tiny bit bigger, but at least when people ask why Java doesn't have proper MI you could answer 'it does and you do it like this' with an almost straight face.
Jonty

The only problem with this is that with multiple
delegates it kinda falls apart.
When yourFunc() is called on an instance of A, which
function is called?original> If there is an ambiguity from multiple interfaces, just flag it at compile
original> time so that the programmer must add an explicit method.
My suggestion was that if there is any ambiguity then no delegation is made, forcing the programmer to do it manually.
Normally in Java it's no big deal when multiple
interfaces have the same methods in them.Actually, I find it a bit of an odd choice by the language designers allowing same signature functions defined in different interfaces to not generate a name clash. Normally this indicates that there is, or soon will be, a bug. I can't think of any situation where this is good programming - if you want the method to exist in both interfaces then it should be defined in a third and inherited into both. This makes it clear that it really is the same method.
Not saying that delegates are a bad idea, but simple
examples don't prove that delegates are a worthwhile
feature to add.The point is that delegation is a commonly used pattern, and is almost always trotted out as a good way of getting most of multiple inheritance. The comments so far are about the problems with this pattern, not with my suggestion to make it easier to use.

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.

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.

Why is multiple inheritance bad?

Hi all,
Can someone give me examples explaining why multiple
inheritence is bad?
My arguments, why the absence multiple inheritence
is bad are below:
1) The absence of multiple inheritance gives me sometimes
headaches. If I implement an interface for overriding just
one method, I must then in some cases (likely in
AWT-programming) "empty-implement" 10 other methods.
2) If I use the adapter class to avoid this, then I cannot
derive my class from another one.

In my opinion, the lack of multiple inheritance is
not a real problem. You can easily bypass this using
a delegate pattern. Example:
class Base1 {
public void method1() {
class Base2 {
public void method2() {
If you want to create a class which inherits from
Base1 and Base2, take the following approach:
Create Interfaces for Base1 and Base2:
intface BaseInterface1 {
public void method1();
interface BaseInterface22 {
public void method2();
Now, let Base1 and Base2 implement the Interfaces.
class Base1 implements Base1Interface {
public void method1() {
class Base2 implements Base2Interface {
public void method2() {
The the subclass can inherit from one baseclass
and implement the other one. Base2 is an attribute
(instance variable) of the new class:
class Devided extends Base1 implements Base2Interface {
Base2 base2;
// Methods of Base2Interface:
public void method2() {
base2.method2();
This looks like a lot of handcraft, but modern IDEs
like Eclipse or VisualAge (ok, not really modern)
give the developer the advantages of self-written
plug-ins. Using such a plug-in, you can easily
automate the creation of the interfaces and the
delegate. In my previous company we wrote several
"wizards" for VisualAge to prevent us from doing
stupid steps again and again.

Problem while Binding multiple Parameters to View Object[Solved]

Hello,
I am facing problem while binding multiple parameters with different data types in View Object query. For example suppose I have following query in my view object.
SELECT Header.ADDED_BY
Header.BATCH_ID,
FROM BATCH_HEADER Header
WHERE :1='deptAdmin' and Header.BATCH_ID
in
select batch_id from batch_header_dept_mapping where dept_id in(SELECT * FROM TABLE(CAST(:0 AS TABLE_OF_VARCHAR)))
I am able to pass the Bind variables of Array type for : 0 , using Steve's ArrayOfStringDomain example. (ArrayOfStringDomain) .
But after passing value to second bind parameter ie.. :1 .
I am getting the error as follows.
## Detail 0 ##
java.sql.SQLSyntaxErrorException: ORA-00932: inconsistent datatypes: expected - got CHAR.
I tried to set
setWhereClauseParam(1,11); // 11 is Number
setWhereClauseParam(0,arr); // arr is arr = new Array(descriptor,conn,deptid); for in parameter.
But of no use , Please let me know if any thing missing form me or have any another solutions. Also please provide me any example if have.
Thank you,
Sandeep
Edited by: user11187811 on Oct 23, 2009 7:27 AM
Edited by: user11187811 on Oct 26, 2009 12:52 AM
Edited by: user11187811 on Oct 26, 2009 6:51 AM

hi.
but when using non-Oracle named parameter binding styles as you've done (ie. , :1), regardless of what number you give each bind variable, they are sequenced 0, 1, 2 etc. As such your bind variable :1 is the 0th parameter, and your bind variable is the 1st parameter.Your statment is correct.
:1 i used was actually on 0th position and :0 was on 1 position. Like you said in sequence 0,1,2 etc. Now i get the answer and i corrected My mistake by assigning right values to right binding variable. and problem just solve.
Thanks Chris.

Problems of no multiple inheritance.

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