Why should the static field be accessed in a static way

Question

public enum MyUnits       MILLSECONDS 1   milliseconds    SECONDS 2   seconds   MINUTES 3  minutes    HOURS 4   hours         private MyUnits int quantity  String units                this quantity   quantity          this units   units             private int quantity      private  String units    public String toString           return  quantity         units        public static void main String   args          for  MyUnits m   MyUnits values                  System out println m MILLSECONDS           System out println m SECONDS           System out println m MINUTES           System out println m HOURS                This is referring to post   wasnt able to reply or comment to any so created a new one  Why are my   System out println m MILLSECONDS     giving warnings-The static field MyUnits MILLSECONDS should be accessed in a static way   Thanks

User · Answer

There s actually a good reason   The non-static access does not always work  for reasons of ambiguity   Suppose we have two classes  A and B  the latter being a subclass of A  with static fields with the same name   public class A       public static String VALUE    Aaa      public class B extends A       public static String VALUE    Bbb       Direct access to the static variable   A VALUE    Aaa   B VALUE    Bbb     Indirect access using an instance  gives a compiler warning that VALUE should be statically accessed    new B   VALUE    Bbb     So far  so good  the compiler can guess which static variable to use  the one on the superclass is somehow farther away  seems somehow logical   Now to the point where it gets tricky  Interfaces can also have static variables   public interface C       public static String VALUE    Ccc      public interface D       public static String VALUE    Ddd       Let s remove the static variable from B  and observe following situations    B implements C  D  B extends A implements C  B extends A implements C  D B extends A implements C where A implements D B extends A implements C where C extends D       The statement new B   VALUE is now ambiguous  as the compiler cannot decide which static variable was meant  and will report it as an error       error  reference to VALUE is ambiguous    both variable VALUE in C and variable VALUE in D match   And that s exactly the reason why static variables should be accessed in a static way

User · Answer

Because     it  MILLISECONDS  is a static field  hiding in an enumeration  but that s what it is      however it is being invoked upon an instance of the given type  but see below as this isn t really true1    javac will  accept  that  but it should really be MyUnits MILLISECONDS  or non-prefixed in the applicable scope    1 Actually  javac  rewrites  the code to the preferred form -- if m happened to be null it would not throw an NPE at run-time -- it is never actually invoked upon the instance    Happy coding     I m not really seeing how the question title fits in with the rest  -  More accurate and specialized titles increase the likely hood the question answers can benefit other programmers

User · Answer

Because when you access a static field  you should do so on the class  or in this case the enum    As in  MyUnits MILLISECONDS    Not on an instance as in  m MILLISECONDS    Edit To address the question of why  In Java  when you declare something as static  you are saying that it is a member of the class  not the object  hence why there is only one    Therefore it doesn t make sense to access it on the object  because that particular data member is associated with the class

[java] Why should the static field be accessed in a static way?

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