Can a static nested class be instantiated in Java?

Question

From Oracle's Java tutorials I've found this text:

As with class methods and variables, a static nested class is associated with its outer class. And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class — it can use them only through an object reference.

Note: 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.

Static nested classes are accessed using the enclosing class name:

OuterClass.StaticNestedClass

For example, to create an object for the static nested class, use this syntax:

OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();

I thought it is not possible to instantiate a static class, so I don't really understand the sentence in bold.

Do you have any idea what it means?

Answer 1

Static nested classes are themselves not static at all. In java, no class is static. Static keyword in static nested classes implies that it is another static member of the outer class. But it is just another raw class . Thats why we can instantiate this class

Answer 2

You are confusing static with abstract. Abstract classes can not be instantiated. static is not a valid qualifier for top level classes, but the meaning for inner classes is the one you quoted.

Answer 3

I guess you misunderstood the static class a little bit. It's true that every abstract class and interface cannot be instantiated, but you do can instantiate an static class. One thing you should notice is that every static class is a nested static class. You cannot just create a static class, as you can see: try to create a new class in eclipse

A static class always belongs to the "parent class" which encloses it, and the difference between static and non-static class is: You can refer to the child static class just like a static property of the "parent class":

ParentClass.NestedStaticClass nestedstatic = new ParentClass.NestedStaticClass();

but you can only make reference to the non-static nested class by instantiating a parent class, like this:

ParentClass parent = new ParentClass();
ParentClass.NestedClass nested = parent.new NestedClass();

The difference is just like that between the static and non-static field.

Answer 4

Too long, didn't read: Every Concrete Class can be instantiated.

We should not expect a Concrete Static Nested Class to function identically as Static variables and Static methods, when it comes to calling and instantiation.

What do I mean by that? When we create variables and methods they can be either static or non-static. The keyword in the previous sentence is "either".

Static meaning they belong to the class and we must call them directly, like this:

Class.staticVariable();
Class.staticMethod();

Non-static meaning they belong to an Instance of that Class and we must call them like this:

Class obj = new Class();
System.out.println(obj.nonStaticVariable);
obj.nonStaticMethod();

But here we are talking about a Class, not a variable or a method. Every Concrete Class can be instantiated. Thus we should not expect a Concrete Static Nested Class, to not be instantiable.