Inner Class

 Inner Class:

- An inner class is a class that is defined within another class and belongs to the instance of the outer class.

- Unlike nested static classes, inner classes have access to the instance variables and methods of the outer class.

- Inner classes can be non-static or static.

Example:

class Outer {

    private int outerVar;

    class Inner {

        void display() {

            System.out.println("Inner class method, outerVar = " + outerVar);

        }

    }

}

Explanation:

In the example above, the Inner class is an inner class of the Outer class. It has access to the private member `outerVar` of the Outer class.

Sample Use:

Inner classes are useful when you want to encapsulate related functionality within a class and you don't want the inner class to be visible outside of its outer class. They are commonly used in event handling, GUI programming, and implementing data structures.

Analogy:

Imagine a car (Outer class) with various components like engine, wheels, and transmission. The engine (Inner class) is an integral part of the car and has direct access to the car's components. Similarly, inner classes are tightly coupled with their outer class and can access its members directly, making them suitable for implementing closely related functionality.

Nested Class vs Inner Class:

1. Nested Class:

   - A nested class is any class that is defined within another class, irrespective of whether it is static or non-static.

   - Nested classes can be static or non-static, and they can have any access modifier.

   - They are primarily used for logical grouping and organization of code.

2. Inner Class:

   - An inner class specifically refers to a non-static nested class.

   - Inner classes have access to the instance variables and methods of the outer class.

   - They are tightly coupled with the instance of the outer class and require an instance of the outer class to be instantiated.

   - Inner classes are commonly used for implementing helper classes or callbacks within the scope of the outer class.

Example:

class Outer {

    private int outerVar;

    // Nested Static Class

    static class NestedStatic {

        void display() {

            System.out.println("NestedStatic class method");

        }

    }

    // Inner Class

    class Inner {

        void display() {

            System.out.println("Inner class method, outerVar = " + outerVar);

        }

    }

}

Explanation:

- In the example above, `NestedStatic` is a static nested class, and `Inner` is an inner class.

- `NestedStatic` is accessed using the outer class name (`Outer.NestedStatic`), while `Inner` is accessed using an instance of the outer class (`outerInstance.new Inner()`).

Comparison:

- Nested classes include both static and non-static nested classes, whereas inner classes specifically refer to non-static nested classes.

- Inner classes have access to instance variables and methods of the outer class, while static nested classes do not.

- Inner classes require an instance of the outer class for instantiation, whereas static nested classes do not.

- Inner classes are commonly used for tighter encapsulation and interaction with the outer class's instance members, while static nested classes are used for logical grouping and organization of code.