Difference between Static and final

Question

I m always confused between static and final keywords in java    How are they different

User · Answer

Static is something that any object in a class can call, that inherently belongs to an object type.

A variable can be final for an entire class, and that simply means it cannot be changed anymore. It can only be set once, and trying to set it again will result in an error being thrown. It is useful for a number of reasons, perhaps you want to declare a constant, that can't be changed.

Some example code:

class someClass
{
   public static int count=0;
   public final String mName;

   someClass(String name)
   {
     mname=name;
     count=count+1;
   }

  public static void main(String args[])
  {
    someClass obj1=new someClass("obj1");
    System.out.println("count="+count+" name="+obj1.mName);
    someClass obj2=new someClass("obj2");
    System.out.println("count="+count+" name="+obj2.mName);
  }
}

Wikipedia contains the complete list of java keywords.

User · Answer

Static variable values can get changed although one copy of the variable traverse through the application  whereas Final Variable values can be initialized once and cannot be changed throughout the application

User · Answer

static means it belongs to the class not an instance  this means that there is only one copy of that variable method shared between all instances of a particular Class   public class MyClass       public static int myVariable   0        Now in some other code creating two instances of MyClass   and altering the variable will affect all instances  MyClass instance1   new MyClass    MyClass instance2   new MyClass     MyClass myVariable   5     This change is reflected in both instances   final is entirely unrelated  it is a way of defining a once only initialization   You can either initialize when defining the variable or within the constructor  nowhere else   note A note on final methods and final classes  this is a way of explicitly stating that the method or class can not be overridden   extended respectively   Extra Reading So on the topic of static  we were talking about the other uses it may have  it is sometimes used in static blocks   When using static variables it is sometimes necessary to set these variables up before using the class  but unfortunately you do not get a constructor   This is where the static keyword comes in   public class MyClass        public static List lt String gt  cars   new ArrayList lt String gt          static           cars add  Ferrari            cars add  Scoda              public class TestClass        public static void main String args              System out println MyClass cars get 0       This will print Ferrari           You must not get this confused with instance initializer blocks which are called before the constructor per instance

User · Answer

The two really aren t similar  static fields are fields that do not belong to any particular instance of a class   class C       public static int n   42      Here  the static field n isn t associated with any particular instance of C but with the entire class in general  which is why C n can be used to access it   Can you still use an instance of C to access n  Yes - but it isn t considered particularly good practice   final on the other hand indicates that a particular variable cannot change after it is initialized   class C       public final int n   42      Here  n cannot be re-assigned because it is final  One other difference is that any variable can be declared final  while not every variable can be declared static   Also  classes can be declared final which indicates that they cannot be extended   final class C     class B extends C        error    Similarly  methods can be declared final to indicate that they cannot be overriden by an extending class   class C       public final void foo         class B extends C       public void foo          error

User · Answer

final -  1 When we apply  final  keyword  to a variable the value of that variable remains constant               or    Once we declare a variable as final the value of that variable cannot be changed   2 It is useful when a variable value does not change during the life time of a program  static -  1 when we apply  static  keyword to a variable  it means it belongs to class     2 When we apply  static  keyword to a method it means the method can be accessed without creating any instance of the class

User · Answer

static means there is only one copy of the variable in memory shared by all instances of the class    The final keyword just means the value can t be changed  Without final  any object can change the value of the variable

User · Answer

Think of an object like a Speaker  If Speaker is a class  It will have different variables such as volume  treble  bass  color etc  You define all these fields while defining the Speaker class  For example  you declared the color field with a static modifier  that means you re telling the compiler that there is exactly one copy of this variable in existence  regardless of how many times the class has been instantiated    Declaring   static final String color    Black      will make sure that whenever this class is instantiated  the value of color field will be  Black  unless it is not changed   public class Speaker    static String color    Black       public class Sample    public static void main String args          System out println Speaker color     will provide output as  Black              Speaker color    white       System out println Speaker color      will provide output as  White       Note   Now once you change the color of the speaker as final this code wont execute  because final keyword makes sure that the value of the field never changes   public class Speaker    static final String color    Black       public class Sample    public static void main String args          System out println Speaker color     should provide output as  Black              Speaker color    white     Error because the value of color is fixed        System out println Speaker color     Code won t execute       You may copy paste this code directly into your emulator and try

User · Answer

Easy Difference   Final   means that the Value of the variable is Final and it will not change anywhere  If you say that final x   5 it means x can not be changed its value is final for everyone   Static   means that it has only one object  lets suppose you have x   5  in memory there is x   5 and its present inside a class  if you create an object or instance of the class which means there a specific box that represents that class and its variables and methods  and if you create an other object or instance of that class it means there are two boxes of that same class which has different x inside them in the memory  and if you call both x in different positions and change their value then their value will be different  box 1 has x which has x  5 and box 2 has x   6  but if you make the x static it means it can not be created again   you can create object of class but that object will not have different x in them   if x is static then box 1 and box 2 both will have the same x which has the value of 5  Yes i can change the value of static any where as its not final  so if i say box 1 has x and i change its value to x  5 and after that i make another box which is box2 and i change the value of box2 x to x 6  then as X is static both boxes has the same x  and both boxes will give the value of box as 6 because box2 overwrites the value of 5 to 6   Both final and static are totally different  Final which is final can not be changed  static which will remain as one but can be changed     This is an example  remember static variable are always called by their class name  because they are only one for all of the objects of that class  so  Class A has x  5   i can call and change it by A x 6

User · Answer

The static keyword can be used in 4 scenarios   static variables   static methods   static blocks of code static nested class   Let s look at static variables and static methods first   Static variable   It is a variable which belongs to the class and not to object  instance    Static variables are initialized only once  at the start of the execution  These variables will be initialized first  before the initialization of any instance variables  A single copy to be shared by all instances of the class    A static variable can be accessed directly by the class name and doesn   t need any object  Syntax  Class variable   Static method   It is a method which belongs to the class and not to the object  instance     A static method can access only static data  It can not access non-static data  instance variables  unless it has creates an instance of the class    A static method can call only other static methods and can not call a non-static method from it unless it has creates an instance of the class    A static method can be accessed directly by the class name and doesn   t need any object  Syntax  Class methodName     A static method cannot refer to this or super keywords in anyway    Static class  Java also has  static nested classes   A static nested class is just one which doesn t implicitly have a reference to an instance of the outer class   Static nested classes can have instance methods and static methods   There s no such thing as a top-level static class in Java   Side note      main method is static since it must be be accessible for an application to run before any instantiation takes place    final keyword is used in several different contexts to define an entity which cannot later be changed    A final class cannot be subclassed  This is done for reasons of security and efficiency  Accordingly  many of the Java standard library classes are final  for example java lang System and java lang String  All methods in a final class are implicitly final  A final method can t be overridden by subclasses  This is used to prevent unexpected behavior from a subclass altering a method that may be crucial to the function or consistency of the class    A final variable can only be initialized once  either via an initializer or an assignment statement  It does not need to be initialized at the point of declaration  this is called a blank final variable  A blank final instance variable of a class must be definitely assigned at the end of every constructor of the class in which it is declared  similarly  a blank final static variable must be definitely assigned in a static initializer of the class in which it is declared  otherwise  a compile-time error occurs in both cases      Note  If the variable is a reference  this means that the variable cannot be re-bound to reference another object  But the object that it references is still mutable  if it was originally mutable   When an anonymous inner class is defined within the body of a method  all variables declared final in the scope of that method are accessible from within the inner class  Once it has been assigned  the value of the final variable cannot change

User · Answer

Static and final have some big differences   Static variables or classes will always be available from  pretty much  anywhere  Final is just a keyword that means a variable cannot be changed  So if had   public class Test         public final int first   10     public static int second   20      public Test         second   second   1      first   first   1           The program would run until it tried to change the  first  integer  which would cause an error  Outside of this class  you would only have access to the  first  variable if you had instantiated the class  This is in contrast to  second   which is available all the time

User · Answer

I won t try to give a complete answer here  My recommendation would be to focus on understanding what each one of them does and then it should be cleare to see that their effects are completely different and why sometimes they are used together   static is for members of a class  attributes and methods  and it has to be understood in contrast to instance  non static  members  I d recommend reading  Understanding Instance and Class Members  in The Java Tutorials  I can also be used in static blocks but I would not worry about it for a start   final has different meanings according if its applied to variables  methods  classes or some other cases  Here I like Wikipedia explanations better

[java] Difference between Static and final?

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