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Static final fields and final fields  RSS feed

 
Greenhorn
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Static final fields and final fields. What is the difference between the two?



 
Ranch Hand
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Uhm, that the one is a static variable and the other one an instance variable ?
 
Greenhorn
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static members belong to the class whereas non-static members belong to the object instance.
 
Marshal
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Welcome to JavaRanch

"Static" is one of those things often not well explained. I wrote here about "Campbell's classification" and suggested when method might be made static. Anything marked static belongs to the class, not a particular object, and you can see examples if you explore the Math class. Code in a static method is prohibited from accessing instance methods or instance fields or using the keywords this and super. That is because those things all belong to the object, and anything static belongs to the class. "Class cannot access object."

Fields marked static belong to the class
  • There is one copy of the field
  • All members of the class have access to that static field.
  • All instances of the class have access to it ("object can access class").
  • There is only one copy of that static field, (still only one copy ) so access from objects is on a shared basis.
  • If one object can change a static field, then all other objects of that class "see" the change.
  • Fields marked final can be set up once and once only. Fields which are set up immediately can be used as constants, and should be static because there is no point in having multiple copies of the same information which won't change.
     
    Ranch Hand
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    v1 is instance variable & v2 is class variable. class variable is one which is member variable of class but is static.
     
    Campbell Ritchie
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    I forgot to say you usually call static members by ClassName.memberName, not objectName.memberName.
     
    Ranch Hand
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    Thankyou Mr Campbell . This was extremely helpful.
     
    Campbell Ritchie
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    You're welcome
     
    It is sorta covered in the JavaRanch Style Guide.
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