Are static methods inherited in Java?

Question

I was reading A Programmer’s Guide to Java™ SCJP Certification by Khalid Mughal.

In the Inheritance chapter, it explains that

Inheritance of members is closely tied to their declared accessibility. If a superclass member is accessible by its simple name in the subclass (without the use of any extra syntax like super), that member is considered inherited

It also mentions that static methods are not inherited. But the code below is perfectlly fine:

class A
{
    public static void display()
    {
        System.out.println("Inside static method of superclass");
    }
}

class B extends A
{
    public void show()
    {
        // This works - accessing display() by its simple name -
        // meaning it is inherited according to the book.
        display();
    }
}

How am I able to directly use display() in class B? Even more, B.display() also works.

Does the book's explanation only apply to instance methods?

Answer 1

Static methods are inherited in Java but they don't take part in polymorphism. If we attempt to override the static methods they will just hide the superclass static methods instead of overriding them.

Answer 2

Static methods in Java are inherited, but can not be overridden. If you declare the same method in a subclass, you hide the superclass method instead of overriding it. Static methods are not polymorphic. At the compile time, the static method will be statically linked.

Example:

public class Writer {
    public static void write() {
        System.out.println("Writing");
    }
}

public class Author extends Writer {
    public static void write() {
        System.out.println("Writing book");
    }
}

public class Programmer extends Writer {

    public static void write() {
        System.out.println("Writing code");
    }

    public static void main(String[] args) {
        Writer w = new Programmer();
        w.write();

        Writer secondWriter = new Author();
        secondWriter.write();

        Writer thirdWriter = null;
        thirdWriter.write();

        Author firstAuthor = new Author();
        firstAuthor.write();
    }
}

You'll get the following:

Writing
Writing
Writing
Writing book

Answer 3

Many have voiced out their answer in words. This is an extended explanation in codes:

public class A {
    public static void test() {
        System.out.println("A");
    }
    public static void test2() {
        System.out.println("Test");
    }
}

public class B extends A {
    public static void test() {
        System.out.println("B");
    }
}

// Called statically
A.test();
B.test();
System.out.println();

// Called statically, testing static inheritance
A.test2();
B.test2();
System.out.println();

// Called via instance object
A a = new A();
B b = new B();
a.test();
b.test();
System.out.println();

// Testing inheritance via instance call
a.test2();
b.test2();
System.out.println();

// Testing whether calling static method via instance object is dependent on compile or runtime type
((A) b).hi();
System.out.println();

// Testing whether null instance works
A nullObj = null;
nullObj.hi();

Results:

A
B

Test
Test

A
B

Test
Test

A

A

Therefore, this is the conclusion:

1. When we call the static in a static manner via ., it will look for the static defined in that class, or the class nearest to that in the inheritance chain. This proves that static methods are inherited.
2. When static method is called from an instance, it calls the static method defined in the compile-time type.
3. Static method can be called from a null instance. My guess is that the compiler will use the variable type to find the class during compilation, and translate that to the appropriate static method call.

Answer 4

We can declare static methods with same signature in subclass, but it is not considered overriding as there won’t be any run-time polymorphism.Because since all static members of a class are loaded at the time of class loading so it decide at compile time(overriding at run time) Hence the answer is ‘No’.

Answer 5

All methods that are accessible are inherited by subclasses.

From the Sun Java Tutorials:

A subclass inherits all of the public and protected members of its parent, no matter what package the subclass is in. If the subclass is in the same package as its parent, it also inherits the package-private members of the parent. You can use the inherited members as is, replace them, hide them, or supplement them with new members

The only difference with inherited static (class) methods and inherited non-static (instance) methods is that when you write a new static method with the same signature, the old static method is just hidden, not overridden.

From the page on the difference between overriding and hiding.

The distinction between hiding and overriding has important implications. The version of the overridden method that gets invoked is the one in the subclass. The version of the hidden method that gets invoked depends on whether it is invoked from the superclass or the subclass

Answer 6

Static method is inherited in subclass but it is not polymorphism. When you writing the implementation of static method, the parent's class method is over hidden, not overridden. Think, if it is not inherited then how you can be able to access without classname.staticMethodname();?