Java Static vs inner class

Question

What is the difference between static and non-static nested class

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static inner class   can declare static  amp  non static members but can only access static members of its parents class   non static inner class  can declare only non static members but can access static and non static member of its parent class

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Static inner class cannot access non-static members of enclosing class  It can directly access static members  instance field and methods  of enclosing class same like the procedural style of getting value without creating object  Static inner class can declare both static and non-static members  The static methods have access to static members of main class  However  it cannot access non-static inner class members  To access members of non-static inner class  it has to create object of non-static inner class  Non-static inner class cannot declare static field and static methods  It has to be declared in either static or top level types  You will get this error on doing so saying  static fields only be declared in static or top level types   Non-static inner class can access both static and non-static members of enclosing class in procedural style of getting value  but it cannot access members of static inner class  The enclosing class cannot access members of inner classes until it creates an object of inner classes  IF main class in accessing members of non-static class it can create object of non-static inner class  If main class in accessing members of static inner class it has two cases    Case 1  For static members  it can use class name of static inner class Case 2  For non-static members  it can create instance  of static inner class

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Let s look in the source of wisdom for such questions  Joshua Bloch s Effective Java   Technically  there is no such thing as a static inner class  According to Effective Java  the correct terminology is a static nested class  A non-static nested class is indeed an inner class  along with anonymous classes and local classes   And now to quote       Each instance of a non-static nested class is implicitly associated   with an enclosing instance of its containing class    It is possible   to invoke methods on the enclosing instance    A static nested class does not have access to the enclosing instance  It uses less space too

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An inner class  by definition  cannot be static  so I am going to recast your question as  What is the difference between static and non-static nested classes    A non-static nested class has full access to the members of the class within which it is nested  A static nested class does not have a reference to a nesting instance  so a static nested class cannot invoke non-static methods or access non-static fields of an instance of the class within which it is nested

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An inner class cannot be static  so I am going to recast your question as  What is the difference between static and non-static nested classes     as u said here inner class cannot be static    i found the below code which is being given static    reason  or which is correct      Yes  there is nothing in the semantics of a static nested type that would stop you from doing that  This snippet runs fine       public class MultipleInner           static class Inner                    public static void main String   args            for  int i   0  i  lt  100  i                  new Inner                        this is a code posted in this website     for the question---  Can a Static Nested Class be Instantiated Multiple Times   answer was---   Now  of course the nested type can do its own instance control  e g  private constructors  singleton pattern  etc  but that has nothing to do with the fact that it s a nested type  Also  if the nested type is a static enum  of course you can t instantiate it at all   But in general  yes  a static nested type can be instantiated multiple times   Note that technically  a static nested type is not an  inner  type

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A static nested class interacts with the instance members of its outer class  and other classes  just like any other top-level class  In effect  a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience

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There are two differences between static inner and non static inner classes    In case of declaring member fields and methods  non static inner class cannot have static fields and methods  But  in case of static inner class  can have static and non static fields and method  The instance of non static inner class is created with the reference of object of outer class  in which it has defined  this means it has enclosing instance  But the instance of static inner class is created without the reference of Outer class  which means it does not have enclosing instance    See this example   class A       class B                  static int x  not allowed here            static class C               static int x     allowed here          class Test       public static void main String    str                A a   new A                Non-Static Inner Class            Requires enclosing instance         A B obj1   a new B                 Static Inner Class            No need for reference of object to the outer class         A C obj2   new A C

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Discussing nested classes     The difference is that a nested class declaration that is also static can be instantiated outside of the enclosing class   When you have a nested class declaration that is not static  Java won t let you instantiate it except via the enclosing class  The object created out of the inner class is linked to the object created from the outer class  so the inner class can reference the fields of the outer   But if it s static  then the link does not exist  the outer fields cannot be accessed  except via an ordinary reference like any other object  and you can therefore instantiate the nested class by itself

[java] Java: Static vs inner class

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