A Comprehensive Guide to Java Inner Classes

Introduction

Java provides a feature called inner classes, which allows a class to be defined within another class. Inner classes help in logically grouping classes that are only used within a specific context, making the code more readable and encapsulated.

Types of Inner Classes in Java

Java provides four types of inner classes:

1. Member Inner Class
2. Static Nested Class
3. Local Inner Class
4. Anonymous Inner Class

1. Member Inner Class

A member inner class is a non-static class defined within another class. It has access to all members of the outer class, including private members.

Example:

class Outer {
    private String message = "Hello from Outer class";
    
    class Inner {
        void display() {
            System.out.println(message);
        }
    }
    
    public static void main(String[] args) {
        Outer outer = new Outer();
        Outer.Inner inner = outer.new Inner();
        inner.display();
    }
}

2. Static Nested Class

A static nested class is a static class inside another class. It does not have access to instance variables of the outer class unless passed explicitly.

Example: