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 static modifier.
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.
1 2 3 4 5 6 7 8 9 | public class Vehicle { private static String vehicleType; public static String getVehicleType(){ return vehicleType; }} |
The static modifier allows us to access the variable vehicleType and the method getVehicleType() using the class name itself, as follows:
Vehicle.vehicleTypeVehicle.getVehicleType()
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:
1 2 3 4 5 6 | class OuterClass { //code class NestedClass { //code }} |
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.
1 2 3 4 5 6 7 8 9 | class OuterClass { //code static class StaticNestedClass { //code } class InnerClass { //code }} |
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:
OuterClass.java
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | package com.javacodegeeks.javabasics.staticclass;public class OuterClass { public static void main(String[] args) { //nested static class doesn't need instantiation of the outer class OuterClass.NestedStaticClass nestedStatic = new OuterClass.NestedStaticClass(); nestedStatic.printMethodNestedStatic(); //inner class needs instantiation of the outer class OuterClass outer = new OuterClass(); OuterClass.InnerClass inner = outer.new InnerClass(); inner.printMethodInner(); } // Static nested class public static class NestedStaticClass { public void printMethodNestedStatic() { System.out.println("Method of nested static class"); } } // inner (non-static nested) class public class InnerClass { public void printMethodInner() { System.out.println("Method of inner(non-static nested) class"); } }} |
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.
Output
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
