Nested Classes in Java

In Java, it is possible to define a class within another class, such classes are known as nested classes. They enable you to logically group classes that are only used in one place, thus this increases the use of encapsulation and creates more readable and maintainable code.

• The scope of a nested class is bounded by the scope of its enclosing class. Thus in the below example, the class NestedClass does not exist independently of the class OuterClass.
• A nested class has access to the members, including private members, of the class in which it is nested. But the enclosing class does not have access to the member of the nested class.
• A nested class is also a member of its enclosing class.
• As a member of its enclosing class, a nested class can be declared private, public, protected, or package-private(default).
• Nested classes are divided into two categories:
  1. static nested class: Nested classes that are declared static are called static nested classes.
  2. inner class: An inner class is a non-static nested class.

Syntax:

class OuterClass
{
...
 class NestedClass
 {
 ...
 }
}

👁 d

Static nested classes

In the case of normal or regular inner classes, without an outer class object existing, there cannot be an inner class object. i.e., an object of the inner class is always strongly associated with an outer class object. But in the case of static nested class, Without an outer class object existing, there may be a static nested class object. i.e., an object of a static nested class is not strongly associated with the outer class object. 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. They 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();

Below is the implementation of the above method:

outer_x = 10
outer_private = 30
outer_y = 20

Inner classes

To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:

OuterClass.InnerClass innerObject = outerObject.new InnerClass();

There are two special kinds of inner classes :

1. Local inner classes
2. Anonymous inner classes

outer_x = 10
outer_y = 20
outer_private = 30

Comparison between a normal or regular class and a static nested class