What does “Static factories returned object need not exist” mean?









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While reading "Effective Java" J.Bloch came across this statement




A fifth advantage of static factories is that the class of the returned object need not exist when the class containing the method is written.




What does it mean? Can someone explain it with some examples ?










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    up vote
    4
    down vote

    favorite












    While reading "Effective Java" J.Bloch came across this statement




    A fifth advantage of static factories is that the class of the returned object need not exist when the class containing the method is written.




    What does it mean? Can someone explain it with some examples ?










    share|improve this question









    New contributor




    gg ff is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.





















      up vote
      4
      down vote

      favorite









      up vote
      4
      down vote

      favorite











      While reading "Effective Java" J.Bloch came across this statement




      A fifth advantage of static factories is that the class of the returned object need not exist when the class containing the method is written.




      What does it mean? Can someone explain it with some examples ?










      share|improve this question









      New contributor




      gg ff is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      While reading "Effective Java" J.Bloch came across this statement




      A fifth advantage of static factories is that the class of the returned object need not exist when the class containing the method is written.




      What does it mean? Can someone explain it with some examples ?







      java






      share|improve this question









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      gg ff is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question









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      gg ff is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      share|improve this question




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      edited Nov 10 at 15:53









      Koray Tugay

      8,38026109214




      8,38026109214






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      asked Nov 10 at 15:50









      gg ff

      234




      234




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          It means that the API of your static factory method can return an interface type, of which the implementation won't be written or generated until later.



          As an example:



          public static MyInterface getMyInterfaceInstance() 
          //load instance dynamically and return it.



          In this case, the factory method only needs the MyInterface interface to exist when it's being compiled. The actual implementation can be loaded dynamically at runtime in many ways, including:



          • Creating a proxy object

          • Reflection (configurable implementation class name loaded at runtime)

          • Looking up a service loader

          In particular, the last two options simply mean that the implementation class can be written in a different module (and many modules can provide an implementation of the interface), and these implementation classes will be discovered at runtime - which makes it possible for the static factory method to be written before the actual implementation class.






          share|improve this answer




















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            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            2
            down vote



            accepted










            It means that the API of your static factory method can return an interface type, of which the implementation won't be written or generated until later.



            As an example:



            public static MyInterface getMyInterfaceInstance() 
            //load instance dynamically and return it.



            In this case, the factory method only needs the MyInterface interface to exist when it's being compiled. The actual implementation can be loaded dynamically at runtime in many ways, including:



            • Creating a proxy object

            • Reflection (configurable implementation class name loaded at runtime)

            • Looking up a service loader

            In particular, the last two options simply mean that the implementation class can be written in a different module (and many modules can provide an implementation of the interface), and these implementation classes will be discovered at runtime - which makes it possible for the static factory method to be written before the actual implementation class.






            share|improve this answer
























              up vote
              2
              down vote



              accepted










              It means that the API of your static factory method can return an interface type, of which the implementation won't be written or generated until later.



              As an example:



              public static MyInterface getMyInterfaceInstance() 
              //load instance dynamically and return it.



              In this case, the factory method only needs the MyInterface interface to exist when it's being compiled. The actual implementation can be loaded dynamically at runtime in many ways, including:



              • Creating a proxy object

              • Reflection (configurable implementation class name loaded at runtime)

              • Looking up a service loader

              In particular, the last two options simply mean that the implementation class can be written in a different module (and many modules can provide an implementation of the interface), and these implementation classes will be discovered at runtime - which makes it possible for the static factory method to be written before the actual implementation class.






              share|improve this answer






















                up vote
                2
                down vote



                accepted







                up vote
                2
                down vote



                accepted






                It means that the API of your static factory method can return an interface type, of which the implementation won't be written or generated until later.



                As an example:



                public static MyInterface getMyInterfaceInstance() 
                //load instance dynamically and return it.



                In this case, the factory method only needs the MyInterface interface to exist when it's being compiled. The actual implementation can be loaded dynamically at runtime in many ways, including:



                • Creating a proxy object

                • Reflection (configurable implementation class name loaded at runtime)

                • Looking up a service loader

                In particular, the last two options simply mean that the implementation class can be written in a different module (and many modules can provide an implementation of the interface), and these implementation classes will be discovered at runtime - which makes it possible for the static factory method to be written before the actual implementation class.






                share|improve this answer












                It means that the API of your static factory method can return an interface type, of which the implementation won't be written or generated until later.



                As an example:



                public static MyInterface getMyInterfaceInstance() 
                //load instance dynamically and return it.



                In this case, the factory method only needs the MyInterface interface to exist when it's being compiled. The actual implementation can be loaded dynamically at runtime in many ways, including:



                • Creating a proxy object

                • Reflection (configurable implementation class name loaded at runtime)

                • Looking up a service loader

                In particular, the last two options simply mean that the implementation class can be written in a different module (and many modules can provide an implementation of the interface), and these implementation classes will be discovered at runtime - which makes it possible for the static factory method to be written before the actual implementation class.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 10 at 16:10









                ernest_k

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                17.6k41836




















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