Java Nested Classes: A Comprehensive Guide with Examples

Introduction:
In Java, nested classes are classes defined within other classes. They provide a way to logically group classes that are only used in one place, and they increase encapsulation and code readability. In this tutorial, we’ll explore the concept of Java nested classes, their types, and how they can be used effectively in your code.

1. What are Nested Classes in Java?
Nested classes in Java are classes that are defined within another class. They allow you to logically group classes that are only used in one place, which increases encapsulation and code organization.

2. Types of Nested Classes:

• Static Nested Classes: These are nested classes that are declared with the static keyword. They can access static members of the outer class and can be instantiated without an instance of the outer class.
• Non-Static Nested Classes (Inner Classes): Also known as inner classes, these are nested classes that are not declared as static. They have access to the members of the outer class and can be instantiated only with an instance of the outer class.
• Member Inner Classes: These are inner classes defined at the member level of another class.
• Local Inner Classes: These are inner classes defined within a method or a scope block.
• Anonymous Inner Classes: These are inner classes without a name, typically used for one-time use.

3. Advantages of Nested Classes:

• Better encapsulation and code organization.
• Increased readability and maintainability.
• Enhanced code reuse and modularity.
• Allows logical grouping of related classes.

4. Examples of Java Nested Classes:
Let’s explore examples of each type of nested class.

// Static Nested Class Example
class Outer {
    static class StaticNested {
        void display() {
            System.out.println("Static nested class");
        }
    }
}

// Member Inner Class Example
class Outer {
    class MemberInner {
        void display() {
            System.out.println("Member inner class");
        }
    }
}

// Local Inner Class Example
class Outer {
    void display() {
        class LocalInner {
            void display() {
                System.out.println("Local inner class");
            }
        }
        LocalInner inner = new LocalInner();
        inner.display();
    }
}

// Anonymous Inner Class Example
interface Greeting {
    void greet();
}

class Outer {
    void display() {
        Greeting greet = new Greeting() {
            @Override
            public void greet() {
                System.out.println("Hello from anonymous inner class");
            }
        };
        greet.greet();
    }
}

5. Conclusion:
Java nested classes are a powerful feature that allows you to organize your code better and improve encapsulation. By understanding the different types of nested classes and their advantages, you can write cleaner, more maintainable Java code. Experiment with nested classes in your projects to see how they can enhance your development experience.