Why can't static methods be abstract in Java?

Question

Because "abstract" means: "Implements no functionality", and "static" means: "There is functionality even if you don't have an object instance". And that's a logical contradiction.

Poor language design. It would be much more effective to call directly a static abstract method than creating an instance just for using that abstract method. Especially true when using an abstract class as a workaround for enum inability to extend, which is another poor design example. Hope they solve those limitations in a next release.

You can't override a static method, so making it abstract would be meaningless. Moreover, a static method in an abstract class would belong to that class, and not the overriding class, so couldn't be used anyway.

The abstract annotation to a method indicates that the method MUST be overriden in a subclass.

In Java, a static member (method or field) cannot be overridden by subclasses (this is not necessarily true in other object oriented languages, see SmallTalk.) A static member may be hidden, but that is fundamentally different than overridden.

Since static members cannot be overriden in a subclass, the abstract annotation cannot be applied to them.

As an aside - other languages do support static inheritance, just like instance inheritance. From a syntax perspective, those languages usually require the class name to be included in the statement. For example, in Java, assuming you are writing code in ClassA, these are equivalent statements (if methodA() is a static method, and there is no instance method with the same signature):

ClassA.methodA();

and

methodA();

In SmallTalk, the class name is not optional, so the syntax is (note that SmallTalk does not use the . to separate the "subject" and the "verb", but instead uses it as the statemend terminator):

ClassA methodA.

Because the class name is always required, the correct "version" of the method can always be determined by traversing the class hierarchy. For what it's worth, I do occasionally miss static inheritance, and was bitten by the lack of static inheritance in Java when I first started with it. Additionally, SmallTalk is duck-typed (and thus doesn't support program-by-contract.) Thus, it has no abstract modifier for class members.

I also asked the same question , here is why

Since Abstract class says, it will not give implementation and allow subclass to give it

so Subclass has to override the methods of Superclass ,

RULE NO 1 - A static method cannot be overridden

Because static members and methods are compile time elements , that is why Overloading(Compile time Polymorphism) of static methods are allowed rather then Overriding (Runtime Polymorphism)

So , they cant be Abstract .

There is no thing like abstract static <--- Not allowed in Java Universe

This is a terrible language design and really no reason as to why it can't be possible.

In fact, here is a pattern or way on how it can be mimicked in **Java ** to allow you at least be able to modify your own implementations:

public static abstract class Request {                 

        // Static method
        public static void doSomething() {
                getRequest().doSomethingImpl();
        }
        
        // Abstract method
        abstract void doSomethingImpl();

        /////////////////////////////////////////////
        private static Request SINGLETON;
        private static Request get() {
            // If setRequest is never called prior, it will default to a default implementation. Of course you could ignore that too. 
            if ( SINGLETON == null ) {
                return SINGLETON = new RequestImplementationDefault();
            }
            return SINGLETON;
        }
        public static Request set(Request instance){
            return SINGLETON = instance;
        }
        /////////////////////////////////////////////
}

Two implementations:

/////////////////////////////////////////////////////

public static final class RequestImplementationDefault extends Request {
        @Override void doSomethingImpl() {
                System.out.println("I am doing something AAA");
        }
}

/////////////////////////////////////////////////////

public static final class RequestImplementaionTest extends Request {
        @Override void doSomethingImpl() {
                System.out.println("I am doing something BBB");
        }
}

/////////////////////////////////////////////////////

Could be used as follows:

Request.set(new RequestImplementationDefault());

// Or

Request.set(new RequestImplementationTest());

// Later in the application you might use

Request.doSomething();

This would allow you to invoke your methods statically, yet be able to alter the implementation say for a Test environment.

Theoretically, you could do this on a ThreadLocal as well, and be able to set instance per Thread context instead rather than fully global as seen here, one would then be able to do Request.withRequest(anotherRequestImpl, () -> { ... }) or similar.

Real world usually do not require the ThreadLocal approach and usually it is enough to be able to alter implementation for Test environment globally.

Note, that the only purpose for this is to enable a way to retain the ability to invoke methods DIRECTLY, EASILY and CLEANLY which static methods provides while at the same time be able to switch implementation should a desire arise at the cost of slightly more complex implementation.

It is just a pattern to get around having normally non modifiable static code.

• An abstract method is defined only so that it can be overridden in a subclass. However, static methods can not be overridden. Therefore, it is a compile-time error to have an abstract, static method.

  Now the next question is why static methods can not be overridden??

• It's because static methods belongs to a particular class and not to its instance. If you try to override a static method you will not get any compilation or runtime error but compiler would just hide the static method of superclass.