Class is defined inside another class, we call it nested class and this other class is called outer class. In my example above, the Builder is a nested class and the Application is an outer class. A nested class is also divided into two different types: Non-static nested class and Static nested class. How is it in detail? In this tutorial, we will learn about nested classes in Java.<\/p>\n
Non-static nested class<\/h3>\n
Non-static nested classes are also known as Inner classes. We can declare these Inner classes inside another class like the Builder class above, inside some method (Method-local Inner Class), in addition, we also have classes that are not named Anonymous Inner Class.<\/p>\n
Other than declaring a class, we cannot declare it with the private access modifier, for the Inner class we can do this.<\/strong> Like the above example, I can declare class Builder as private as follows:<\/p>\n But once you have declared a private Inner class, it can only be accessed inside the class it is declared!<\/p>\n To initialize an Inner class, you need to initialize the object for the outer class first. For example:<\/p>\n When we declare a class inside a method, called Method-local Inner Class<\/strong>, the scope of this class belongs only to that method. You cannot declare this class with the access modifier in this case. For example:<\/p>\n And thus, we can only instantiate the object of this class inside the method:<\/p>\n You can declare the final class or abstract class inside a method.<\/p>\n Or:<\/p>\n Anonymous Inner Class<\/strong> is often declared when we want to override a certain method of a class or interface. We will declare Anonymous Inner Class and instantiate the object for this class at the same time. For example:<\/p>\n You can also declare Anonymous Inner Class outside the method as follows:<\/p>\n It is a static member of the outer class and therefore we do not need to initialize the object of the outer class and this class itself to access it. For example:<\/p>\n The static nested class will not have access to fields, methods which are non-static of the outer class. Eg:<\/p>\n We cannot declare a static nested class inside the method!<\/p>\n\n\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n\r\n private class Builder {\r\n\r\n }\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n\r\n private class Builder {\r\n\r\n }\r\n\r\n public static void main(String[] args) {\r\n Application app = new Application();\r\n Builder builder = app.new Builder();\r\n }\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n\r\n public void print() {\r\n class Builder {\r\n\r\n }\r\n }\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n\r\n public void print() {\r\n class Builder {\r\n\r\n }\r\n \r\n Builder builder = new Builder();\r\n }\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n private void print() {\r\n abstract class Builder {\r\n\r\n }\r\n }\r\n\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n private void print() {\r\n final class Builder {\r\n\r\n }\r\n }\r\n\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n\r\n public void print() {\r\n Comparable<String> comparable = new Comparable<String>() {\r\n public int compareTo(String o) {\r\n return 0;\r\n }\r\n };\r\n }\r\n}\r\n<\/pre>\npackage com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n \r\n Comparable<String> comparable = new Comparable<String>() {\r\n public int compareTo(String o) {\r\n return 0;\r\n }\r\n };\r\n\r\n public void print() {\r\n \r\n }\r\n}\r\n<\/pre>\nStatic Nested Class<\/h3>\n
package com.huongdanjava.javaexample;\r\n\r\npublic class Application {\r\n\r\n static class Builder {\r\n\r\n private static void print() {\r\n\r\n }\r\n }\r\n\r\n public static void main(String[] args) {\r\n Application.Builder.print();\r\n }\r\n}\r\n<\/pre>\n![\"Nested](\"https:\/\/huongdanjava.com\/wp-content\/uploads\/2021\/04\/nested-class-in-java-1.png\")
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