In this example, we will discuss the purpose of a static class in Java. First of all, let’s give a short explanation of the
For example, in Java, if a field or a method in a class has the static modifier in its declaration, then it is always associated with the class as a whole, rather than with any object of the class.
In the code below we have declared a class named
Vehicle, a class field member named
vehicleType and a method named
getVehicleType(), both declared as
static modifier allows us to access the variable
vehicleType and the method
getVehicleType() using the class name itself, as follows:
Something similar happens to classes that are declared
static, but in order to explain this better, we must first explain the inner classes or generally, the nested classes, because ONLY nested classes can be static.
Java supports the concept of nested classes. Nested classes are classes that can be defined within the body of another class. An example of a nested class is illustrated below:
The OuterClass which contains another class can be also called top-level class.
Nested classes are further divided into two categories: static and non-static. Nested classes that are declared
static are called static nested classes. Non-static nested classes are just called inner classes.
What’s the difference between nested
static classes and non-static (inner) classes?
The main difference is that inner class requires the instantiation of the outer class so as to be initialized and it is always associated with an instance of the enclosing class. On the other hand, a nested
static class is not associated with any instance of the enclosing class. Nested
static classes are declared with the
static keyword, which means than can be accessed like any other static member of class, as we shown before.
1. Example of nested classes
Create a java class named
OuterClass.java with the following code:
As we can observe in the above code, we have declared a class named
OuterClass which is considered to be the outer class or otherwise, the top-level class. Also, we can see that we have declared two more nested classes (they are enclosed in the outer class), one of which is static and the other one is non-static. Finally, we have declared the main method in the outer class, which is static as always (Really, why is that? The answer is that we can call it without creating an instance of a class which contains this main method). We can see that the method of the nested static class can be accessed without creating an object of the
OuterClass, whereas the method of the inner class needs instantiation of the
OuterClass in order to get accessed.
Method of nested static class Method of inner(non-static nested) class
2. Download the source code
This was an example of the
static class in Java.
You can download the source code from here: Static class Java Example