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There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class. [9]
The syntax of Java is the set of rules defining how a Java program is written and interpreted. ... A class implementing an interface must override all its methods ...
Conventional single-dispatch languages like Java also obey this rule: only one argument is used for method selection (the receiver object, passed along to a method as the hidden argument this), and indeed the type of this is more specialized inside overriding methods than in the superclass.
Covariant return types have been (partially) allowed in the Java language since the release of JDK5.0, [2] so the following example wouldn't compile on a previous release: // Classes used as return types: class A { } class B extends A { } // "Class B is narrower than class A" // Classes demonstrating method overriding: class C { A getFoo ...
Method overloading, on the other hand, refers to differentiating the code used to handle a message based on the parameters of the method. If one views the receiving object as the first parameter in any method then overriding is just a special case of overloading where the selection is based only on the first argument.
The method with the most specific argument classes is chosen (D>(B,C)>A) ; then in the order in which parent classes are named in the subclass definition (B>C). However, the programmer can override this, by giving a specific method resolution order or stating a rule for combining methods.
D provides an explicit "alias this" declaration within a type can forward into it every method and member of another contained type. [11] Dart provides mixins with default implementations that can be shared. Go type embedding avoids the need for forwarding methods. [12] Java provides default interface methods since version 8.
In object-oriented programming, the factory method pattern is a design pattern that uses factory methods to deal with the problem of creating objects without having to specify their exact classes. Rather than by calling a constructor , this is accomplished by invoking a factory method to create an object.