Class extending more than one class Java

Question

I know that a class can implement more than one interface  but is it possible to extend more than one class  For example I want my class to extend both TransformGroup and a class I created  Is this possible in Java  Both statements class X extends TransformGroup extends Y and class X extends TransformGroup  Y receive an error  And if it is not possible  why  TransformGroup extends Group but I guess it also extends Node since it inherits fields from Node and it can be passed where a Node object is required  Also  like all classes in Java  they extend Object class  So why wouldn t it be possible to extend with more than one class     TransformGroup inheritance  So  if that is possible  what is the proper way to do it  And if not  why and how should I solve the problem

User · Answer

Hello please note like real work   Children can not have two mother  So in java  subclass can not have two parent class

User · Answer

In Java multiple inheritance is not permitted   It was excluded from the language as a design decision  primarily to avoid circular dependencies   Scenario1  As you have learned the following is not possible in Java   public class Dog extends Animal  Canine       Scenario 2  However the following is possible   public class Canine extends Animal      public class Dog extends Canine       The difference in these two approaches is that in the second approach there is a clearly defined parent or super class  while in the first approach the super class is ambiguous     Consider if both Animal and Canine had a method drink     Under the first scenario which parent method would be called if we called Dog drink     Under the second scenario  we know calling Dog drink   would call the Canine classes drink method as long as Dog had not overridden it

User · Answer

No it is not possible in java  Maybe in java 8 it will be avilable   Except the case when you extend in a tree   For example   class A class B extends A class C extends B

User · Answer

In Java multiple inheritance is not permitted for implementations  classes  only for interfaces   interface A extends B  C   E g  MouseInputListener extends MouseListener and MouseMotionListener  And  of course  a class can implement several interfaces   class X implements A  F

User · Answer

java can not support multiple inheritence but u can do this in this way  class X     class Y extends X     class Z extends Y

User · Answer

Java does not allow extending multiple classes   Let s assume C class is extending A and B classes  Then if suppose A and B classes have method with same name Ex  method1     Consider the code    C obj1   new C     obj1 method1    - here JVM will not understand to which method it need to access  Because both A and B classes have this method  So we are putting JVM in dilemma  so that is the reason why multiple inheritance is removed from Java  And as said implementing multiple classes will resolve this issue   Hope this has helped

User · Answer

Most of the answers given seem to assume that all the classes we are looking to inherit from are defined by us   But what if one of the classes is not defined by us  i e  we cannot change what one of those classes inherits from and therefore cannot make use of the accepted answer  what happens then   Well the answer depends on if we have at least one of the classes having been defined by us  i e  there exists a class A among the list of classes we would like to inherit from  where A is created by us   In addition to the already accepted answer  I propose 3 more instances of this multiple inheritance problem and possible solutions to each   Inheritance type 1  Ok say you want a class C to extend classes  A and B  where B is a class defined somewhere else  but A is defined by us  What we can do with this is to turn A into an interface then  class C can implement A while extending B   class A    class B       Some external class class C      Turns into  interface A    class AImpl implements A    class B       Some external class class C extends B implements A   Inheritance type 2  Now say you have more than two classes to inherit from  well the same idea still holds - all but one of the classes has to be defined by us  So say we want class A to inherit from the following classes  B  C      X where X is a class which is external to us  i e  defined somewhere else  We apply the same idea of turning all the other classes but the last into an interface then we can have   interface B    class BImpl implements B    interface C    class CImpl implements C        class X    class A extends X implements B  C        Inheritance type 3  Finally  there is also the case where you have just a bunch of classes to inherit from  but none of them are defined by you  This is a bit trickier  but it is doable by making use of delegation  Delegation allows a class A to pretend to be some other class B but any calls on A to some public method defined in B  actually delegates that call to an object of type B and the result is returned  This makes class A what I would call a Fat class  How does this help   Well it s simple  You create an interface which specifies the public methods within the external classes which you would like to make use of  as well as methods within the new class you are creating  then you have your new class implement that interface  That may have sounded confusing  so let me explain better   Initially we have the following external classes B  C  D       X  and we want our new class A to inherit from all those classes   class B       public void foo         class C       public void bar         class D       public void fooFoo              class X       public String fooBar          Next we create an interface A which exposes the public methods that were previously in class A as well as the public methods from the above classes  interface A       void doSomething       previously defined in A     String fooBar       from class X     void fooFoo       from class D     void bar       from class C     void foo       from class B     Finally  we create a class AImpl which implements the interface A   class AImpl implements A          It needs instances of the other classes  so those should be        part of the constructor     public AImpl B b  C c  D d  X x                define the methods within the interface     And there you have it  This is sort of pseudo-inheritance because an object of type A is not a strict descendant of any of the external classes we started with but rather exposes an interface which defines the same methods as in those classes   You might ask  why we didn t just create a class that defines the methods we would like to make use of  rather than defining an interface  i e  why didn t we just have a class A which contains the public methods from the classes we would like to inherit from  This is done in order to reduce coupling  We don t want to have classes that use A to have to depend too much on class A  because classes tend to change a lot   but rather to rely on the promise given within the interface A

User · Answer

There is no concept of multiple inheritance in Java  Only multiple interfaces can be implemented

User · Answer

Java didn t provide multiple inheritance  When you say A extends B then it means that A extends B and B extends Object  It doesn t mean A extends B  Object   class A extends Object class B extends A

User · Answer

Assume B and C are overriding inherited method and their own implementation  Now D inherits both B  amp  C using multiple inheritance  D should inherit the overridden method The Question is which overridden method will be used  Will it be from B or C  Here we have an ambiguity  To exclude such situation multiple inheritance was not used in Java

User · Answer

Multiple inheritance is not possible with class  you can achieve it with the help of interface but not with class  It is by design of java language  Look a comment by James gosling      by James Gosling in February 1995 gives an idea on why multiple   inheritance is not supported in Java       JAVA omits many rarely used  poorly understood  confusing features of   C   that in our experience bring more grief than bene t  This   primarily consists of operator overloading  although it does have   method overloading   multiple inheritance  and extensive automatic   coercions

[java] Class extending more than one class Java?

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