Nested Classes

A class defined within another class is called a Nested Class.

Types of Nested Classes

1. Static Nested Class

A static class inside another class.

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

// Usage
Outer.StaticNested obj = new Outer.StaticNested();
obj.display();

2. Inner Class (Non-static)

Requires an instance of the outer class.

class Outer {
    class Inner {
        void display() {
            System.out.println("Inner class");
        }
    }
}

// Usage
Outer outer = new Outer();
Outer.Inner inner = outer.new Inner();
inner.display();

3. Local Class

Defined inside a method.

class Outer {
    void myMethod() {
        class Local {
            void display() {
                System.out.println("Local class");
            }
        }
        Local local = new Local();
        local.display();
    }
}

4. Anonymous Class

A class without a name, often used for one-time implementations.

interface Greeting {
    void sayHello();
}

Greeting greeting = new Greeting() {
    public void sayHello() {
        System.out.println("Hello from anonymous class!");
    }
};
greeting.sayHello();

When to Use Nested Classes?

Quiz