Can an interface extend multiple interfaces in Java

Question

Can an interface extend multiple interfaces in Java  This code appears valid in my IDE and it does compile   interface Foo extends Runnable  Set  Comparator lt String gt        but I had heard that multiple inheritance was not allowed in Java  Why does there appear to be an exception for interfaces

User · Answer

An interface can extend multiple interfaces     A class can implement multiple interfaces     However  a class can only extend a single class   Careful how you use the words extends and implements when talking about interface and class

User · Answer

Can an interface extend multiple interfaces in java    Answer is  Yes   According to JLS     An interface may be declared to be a direct extension of one or more   other interfaces  meaning that it implicitly specifies all the member   types  abstract methods  and constants of the interfaces it extends    except for any member types and constants that it may hide

User · Answer

Yes  you can do it  An interface can extend multiple interfaces  as shown here   interface Maininterface extends inter1  inter2  inter3          methods     A single class can also implement multiple interfaces  What if two interfaces have a method defining the same name and signature   There is a tricky point   interface A       void test       interface B       void test       class C implements A  B         Override     public void test                      Then single implementation works for both      Read my complete post here   http   codeinventions blogspot com 2014 07 can-interface-extend-multiple html

User · Answer

You can extend multiple Interfaces but you cannot extend multiple classes   The reason that it is not possible in Java to extending multiple classes  is the bad experience from C   where this is possible   The alternative for multipe inheritance is that a class can implement multiple interfaces  or an Interface can extend multiple Interfaces

User · Answer

From the Oracle documentation page about multiple inheritance type we can find the accurate answer here  Here we should first know the type of multiple inheritance in java -   Multiple inheritance of state  Multiple inheritance of implementation  Multiple inheritance of type    Java  doesn t support the multiple inheritance of state  but it support multiple inheritance of implementation with default methods since java 8 release and multiple inheritance of type with interfaces   Then here the question arises for  diamond problem  and how Java deal with that -    In case of multiple inheritance of implementation java compiler gives compilation error and asks the user to fix it by specifying the interface name  Example here -              interface A                   void method                               interface B extends A                    Override                 default void method                         System out println  B                                                 interface C extends A                     Override                 default void method                         System out println  C                                                 interface D extends B  C                     So here we will get error as -      interface D inherits unrelated defaults for method   from types B and C interface D extends B  C  You can fix it like -   interface D extends B  C                    Override                 default void method                         B super method                                       In multiple inheritance of type java allows it because interface doesn t contain mutable fields and only one implementation will belong to the class so java doesn t give any issue and it allows you to do so    In Conclusion we can say that java doesn t support multiple inheritance of state but it does support multiple inheritance of implementation and multiple inheritance of type

User · Answer

A Java class can only extend one parent class  Multiple inheritance is not allowed  Interfaces are not classes  however  and an interface can extend more than one parent interface    for example  take a look here  http   www tutorialspoint com java java interfaces htm

User · Answer

I think your confusion lies with multiple inheritance  in which it is bad practise to do so and in Java this is also not possible   However  implementing multiple interfaces is allowed in Java and it is also safe

[java] Can an interface extend multiple interfaces in Java?

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