V_Inner_Class.java

/**
 * Java supports nesting classes; a class can be a member of another class. Just
 * write a class within a class. Unlike a class, an inner class can be private.
 * Once you declare an inner class private, it cannot be accessed from an object
 * outside the class.
 */
class Robot {
    int id;

    Robot(int i) {
        id = i;
        Brain b = new Brain();
        b.think();
    }

    private class Brain {
        public void think() {
            System.out.println(id + " is thinking");
        }
    }
}

/**
 * The class Robot has an inner class Brain. The inner class can access all of
 * the member variables and methods of its outer class, but it cannot be
 * accessed from any outside class.
 */
public class V_Inner_Class {
    public static void main(String[] args) {
        Robot r = new Robot(1);
    }
}