Why are you not able to declare a class as static in Java

Question

User · Answer

I think this is possible as easy as drink a glass of coffee!. Just take a look at this. We do not use static keyword explicitly while defining class.

public class StaticClass {

    static private int me = 3;
    public static void printHelloWorld() {
       System.out.println("Hello World");
    }



    public static void main(String[] args) {
        StaticClass.printHelloWorld();
        System.out.println(StaticClass.me);
    }
}

Is not that a definition of static class? We just use a function binded to just a class. Be careful that in this case we can use another class in that nested. Look at this:

class StaticClass1 {

    public static int yum = 4;

    static void  printHowAreYou() {
        System.out.println("How are you?");
    }
}

public class StaticClass {

    static int me = 3; 
    public static void printHelloWorld() {
       System.out.println("Hello World");
       StaticClass1.printHowAreYou();
       System.out.println(StaticClass1.yum);
    }



    public static void main(String[] args) {
        StaticClass.printHelloWorld();
        System.out.println(StaticClass.me);
    }
}

User · Answer

public class Outer      public static class Inner            it can be declared static - as long as it is a member class   From the JLS      Member classes may be static  in which case they have no access to the instance variables of the surrounding class  or they may be inner classes    8 1 3     and here      The static keyword may modify the declaration of a member type C within the body of a non-inner class T  Its effect is to declare that C is not an inner class  Just as a static method of T has no current instance of T in its body  C also has no current instance of T  nor does it have any lexically enclosing instances    A static keyword wouldn t make any sense for a top level class  just because a top level class has no enclosing type

User · Answer

Sure they can  but only inner nested classes  There  it means that instances of the nested class do not require an enclosing instance of the outer class   But for top-level classes  the language designers couldn t think of anything useful to do with the keyword  so it s not allowed

User · Answer

Everything we code in java goes into a class  Whenever we run a class JVM instantiates an object  JVM can create a number of objects  by definition Static means you have the same set of copy to all objects   So  if Java would have allowed the top class to be static whenever you run a program it creates an Object and keeps overriding on to the same Memory Location    If You are just replacing the object every time you run it whats the point of creating it   So that is the reason Java got rid of the static for top-Level Class   There might be more concrete reasons but this made much logical sense to me

User · Answer

Only nested classes can be static  By doing so you can use the nested class without having an instance of the outer class  class OuterClass       public static class StaticNestedClass              public class InnerClass              public InnerClass getAnInnerClass             return new InnerClass                 This method doesn t work     public static InnerClass getAnInnerClassStatically             return new InnerClass             class OtherClass         Use of a static nested class      private OuterClass StaticNestedClass staticNestedClass   new OuterClass StaticNestedClass           Doesn t work     private OuterClass InnerClass innerClass   new OuterClass InnerClass           Use of an inner class      private OuterClass outerclass  new OuterClass        private OuterClass InnerClass innerClass2   outerclass getAnInnerClass        private OuterClass InnerClass innerClass3   outerclass new InnerClass       Sources    Oracle tutorial on nested classes  On the same topic    Java  Static vs non static inner class Java inner class and static nested class

User · Answer

One can look at PlatformUI in Eclipse for a class with static methods and private constructor with itself being final   public final class  lt class name gt         static constants      static memebers

User · Answer

So  I m coming late to the party  but here s my two cents - philosophically adding to Colin Hebert s answer   At a high level your question deals with the difference between objects and types   While there are many cars  objects   there is only one Car class  type    Declaring something as static means that you are operating in the  type  space   There is only one   The top-level class keyword already defines a type in the  type  space   As a result  public static class Car  is redundant

User · Answer

In addition to how Java defines static inner classes  there is another definition of static classes as per the C  world  1   A static class is one that has only static methods  functions  and it is meant to support procedural programming  Such classes aren t really classes in that the user of the class is only interested in the helper functions and not in creating instances of the class  While static classes are supported in C   no such direct support exists in Java  You can however use enums to mimic C  static classes in Java so that a user can never create instances of a given class  even using reflection    2    public enum StaticClass2          Empty enum trick to avoid instance creation          this semi-colon is important      public static boolean isEmpty final String s            return s    null    s isEmpty

User · Answer

You can create a utility class  which cannot have instances created  by declaring an enum type with no instances  i e  you are specificly declaring that there are no instances   public enum MyUtilities       public static void myMethod

User · Answer

Top level classes are static by default  Inner classes are non-static by default  You can change the default for inner classes by explicitly marking them static  Top level classes  by virtue of being top-level  cannot have non-static semantics because there can be no parent class to refer to  Therefore  there is no way to change the default for top-level classes

User · Answer

if the benefit of using a static-class was not to instantiate an object and using a method then just declare the class as public and this method as static

User · Answer

As explained above  a Class cannot be static unless it s a member of another Class   If you re looking to design a class  of which there cannot be multiple instances   you may want to look into the  Singleton  design pattern   Beginner Singleton info here   Caveat      If you are thinking of using the   singleton pattern  resist with all   your might  It is one of the easiest   DesignPatterns to understand  probably   the most popular  and definitely the   most abused     source  JavaRanch as linked above

User · Answer

The only classes that can be static are inner classes  The following code works just fine   public class whatever       static class innerclass             The point of static inner classes is that they don t have a reference to the outer class object

User · Answer

Class with private constructor is static   Declare your class like this   public class eOAuth        private eOAuth          public final static int    ECodeOauthInvalidGrant   0x1      public final static int    ECodeOauthUnknown         0x10      public static GetSomeStuff          and you can used without initialization   if  value    eOAuth ECodeOauthInvalidGrant      eOAuth GetSomeStuff

[java] Why are you not able to declare a class as static in Java?

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