Can you write virtual functions methods in Java

Question

Is it possible to write virtual methods in Java  as one would do in C     Or  is there a proper Java approach which you can implement that produces similar behavior  Could I please have some examples

User · Answer

In Java  all public  non-private  variables  amp  functions are Virtual by default   Moreover variables  amp  functions using keyword final are not virtual

User · Answer

All functions in Java are virtual by default   You have to go out of your way to write non-virtual functions by adding the  final  keyword   This is the opposite of the C   C  default   Class functions are non-virtual by default  you make them so by adding the  virtual  modifier

User · Answer

From wikipedia     In Java  all non-static methods are by   default  virtual functions   Only   methods marked with the keyword final    which cannot be overridden  along with   private methods  which are not   inherited  are non-virtual

User · Answer

Yes  you can write virtual  functions  in Java

User · Answer

All non-private instance methods are virtual by default in Java    In C    private methods can be virtual  This can be exploited for the non-virtual-interface  NVI  idiom  In Java  you d need to make the NVI overridable methods protected   From the Java Language Specification  v3      8 4 8 1 Overriding  by Instance Methods  An instance method m1   declared in a class C overrides   another instance method  m2  declared   in class A iff all of the following   are true          C is a subclass of A    The signature of m1 is a subsignature    8 4 2  of the signature   of m2    Either           m2 is public  protected or declared with default access in the   same package as C  or           m1 overrides a method m3  m3 distinct from m1  m3 distinct from   m2  such that m3 overrides m2

User · Answer

Can you write virtual functions in Java   Yes  In fact  all instance methods in Java are virtual by default  Only certain methods are not virtual    Class methods  because typically each instance holds information like a pointer to a vtable about its specific methods  but no instance is available here   Private instance methods  because no other class can access the method  the calling instance has always the type of the defining class itself and is therefore unambiguously known at compile time     Here are some examples    Normal  virtual functions  The following example is from an old version of the wikipedia page mentioned in another answer   import java util     public class Animal       public void eat                System out println  I eat like a generic Animal               public static void main String   args              List lt Animal gt  animals   new LinkedList lt Animal gt            animals add new Animal           animals add new Fish           animals add new Goldfish           animals add new OtherAnimal            for  Animal currentAnimal   animals                    currentAnimal eat                    class Fish extends Animal        Override    public void eat                System out println  I eat like a fish              class Goldfish extends Fish        Override    public void eat                System out println  I eat like a goldfish              class OtherAnimal extends Animal      Output    I eat like a generic Animal  I eat like a fish  I eat like a goldfish  I eat like a generic Animal    Example with virtual functions with interfaces    Java interface methods are all virtual  They must be virtual because they rely on the implementing classes to provide the method implementations  The code to execute will only be selected at run time   For example   interface Bicycle             the function applyBrakes   is virtual because     void applyBrakes          functions in interfaces are designed to be                                overridden   class ACMEBicycle implements Bicycle       public void applyBrakes                    Here we implement applyBrakes          System out println  Brakes applied      function           Example with virtual functions with abstract classes     Similar to interfaces Abstract classes must contain virtual methods because they rely on the extending classes  implementation   For Example   abstract class Dog                          final void bark                     bark   is not virtual because it is          System out println  woof        final and if you tried to override it                                         you would get a compile time error       abstract void jump                  jump   is a  pure  virtual function                                         class MyDog extends Dog      void jump            System out println  boing         here jump   is being overridden                                           public class Runner       public static void main String   args            Dog dog   new MyDog             Create a MyDog and assign to plain Dog variable         dog jump                        calling the virtual function                                          MyDog jump   will be executed                                          although the variable is just a plain Dog

[java] Can you write virtual functions / methods in Java?

Examples related to java

Examples related to virtual

Examples related to virtual-functions