Behaviour of Final Static Method

Behaviour of final static method

Static methods cannot be overridden but they can be hidden. The ts() method of B is not overriding(not subject to polymorphism) the ts() of A but it will hide it. If you call ts() in B (NOT A.ts() or B.ts() ... just ts()), the one of B will be called and not A. Since this is not subjected to polymorphism, the call ts() in A will never be redirected to the one in B.

The keyword final will disable the method from being hidden. So they cannot be hidden and an attempt to do so will result in a compiler error.

Hope this helps.

Is it a bad idea to declare a final static method?

I don't consider it's bad practice to mark a static method as final.

As you found out, final will prevent the method from being hidden by subclasses which is very good news imho.

I'm quite surprised by your statement:

Re-defining method() as final in Foo will disable the ability for Bar to hide it, and re-running main() will output:
in Foo

in Foo

No, marking the method as final in Foo will prevent Bar from compiling. At least in Eclipse I'm getting:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: Cannot override the final method from Foo

Also, I think people should always invoke static method qualifying them with the class name even within the class itself:

class Foo
{
  private static final void foo()
  {
    System.out.println("hollywood!");
  }

  public Foo()
  {
    foo();      // both compile
    Foo.foo();  // but I prefer this one
  }
}

static final method in Java

If you look at JLS 8.4.3.3 final Methods, you'll see that the final method modifier prevents methods from either being overridden or hidden.

A method can be declared final to prevent subclasses from overriding or hiding it.
It is a compile-time error to attempt to override or hide a final method.

A static method cannot be overridden, but it can be hidden. The final modifier prevents it from being hidden by a sub-class static method.

static, final, static final - correct usage and when to use them?

static means that a field or method belongs to the class, as opposed to individual instances of the class.

final actually means different things when applied to methods versus fields (or local variables):

final variables and fields cannot be reassigned. This is fairly similar to C++'s const.
final methods cannot be overridden, which only applies to methods on instances. When used in this sense, final is not similar to C++'s const.

Because you cannot override static methods on classes, the combined modifiers static final are usually redundant, which is why IntelliJ advises you to remove one of the modifiers.

Additional notes:

final variables and fields can refer to instances that may change, even though the references themselves cannot change.
Though you didn't ask about classes, final has a third meaning there: final classes cannot be subclassed. static can also be applied to nested classes (classes within classes), but it has the same meaning: A static nested class does not belong to exactly one instance of the enclosing class, which it would otherwise.
Though static methods cannot be overridden, there's a similar behavior called "shadowing" or "method hiding", by which a subclass offers a static method of the same name and signature as the subclass. This behaves differently from overriding, but similarly, static final methods cannot be shadowed.

Related SO question: "Is it a bad idea to declare a final static method?"

What is the reason for compile warning static method declared final?

Static methods are not subject to overriding.

The final keyword hides the method. See the link in comments for more details.

Note that you should not rely on that behavior, although the language allows it. You should always invoke static methods as <class-name>.<method-name>.

final class with final static methods redundant

Final classes cannot be extended in the first place, so it does not matter whether or not their methods are marked as final.

For example, this will fail:

final class Util {
}
class Extra extends Util {
}

error: cannot inherit from final Util

class Extra extends Util {

Are static functions in a final class implicitly final?

In a final class, all methods are implicitly final as well because making the class final means it cannot be inherited from and thus there can be no hiding or overriding of its methods in child classes.

As a result, effectively you are correct that a static method in a final class is final, but it's not because of the fact that it's a static method. It's because the class is final.

Difference between Static and final?

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.