Inner, static nested and anonymous classes

class Shop {
    private final String name;

    Shop(String name) { this.name = name; }

    class Bill {                                // inner: no 'static'
        int amount;
        Bill(int amount) { this.amount = amount; }

        String print() {
            return name + ": ₹" + amount;       // reads the outer object's private field
        }
    }
}

public class Main {
    public static void main(String[] args) {
        Shop kharghar = new Shop("Chai Point, Kharghar");
        Shop vashi = new Shop("Chai Point, Vashi");

        Shop.Bill b1 = kharghar.new Bill(120);  // a bill OF the Kharghar shop
        Shop.Bill b2 = vashi.new Bill(45);
        System.out.println(b1.print());
        System.out.println(b2.print());
    }
}

class Bank$Account {
  int bal;
  final Bank this$0;          ← the link to the outer object
  Bank$Account(Bank);         ← the constructor receives it
  int interest();
  java.lang.String bank();
}

class Shop {
    static class Tax {                         // static: no Shop object needed
        static int gst(int amount) {
            return amount * 5 / 100;
        }
    }

    static class Address {
        final String city, pin;
        Address(String city, String pin) { this.city = city; this.pin = pin; }
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println(Shop.Tax.gst(120));
        Shop.Address a = new Shop.Address("Navi Mumbai", "410210");   // no shop object
        System.out.println(a.city + " " + a.pin);
    }
}

public class Main {
    static void printReceipt(String customer, int amount) {
        class Line {                               // visible only inside this method
            String text(String label, int value) {
                return label + " for " + customer + ": ₹" + value;   // uses a captured local
            }
        }
        Line l = new Line();
        System.out.println(l.text("Amount", amount));
        System.out.println(l.text("GST", amount * 5 / 100));
    }

    public static void main(String[] args) {
        printReceipt("Riya", 200);
    }
}

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

interface Discount {
    int apply(int price);
}

public class Main {
    public static void main(String[] args) {
        Discount festive = new Discount() {        // class with no name, created at once
            public int apply(int price) {
                return price - price / 10;         // 10% off
            }
        };
        System.out.println(festive.apply(500));

        List<String> names = new ArrayList<>(List.of("Riya", "Kabir", "Om"));
        names.sort(new Comparator<String>() {     // a one-off sort rule
            public int compare(String a, String b) {
                return a.length() - b.length();
            }
        });
        System.out.println(names);
    }
}

int off = 50;
off = 60;                                          // now 'off' changes...
Discount d = new Discount() {
    public int apply(int p) { return p - off; }    // error
};

error: local variables referenced from an inner class must be final or effectively final

interface Offer {
    int apply(int amount);
}

class Stall {
    private final String name;
    private int billCount = 0;

    Stall(String name) { this.name = name; }

    class Bill {                                    // inner: belongs to one stall
        final int no;
        final int amount;

        Bill(int amount) {
            this.amount = amount;
            billCount++;                            // updates the OUTER object's field
            this.no = billCount;
        }

        String print(Offer offer) {
            int pay = offer.apply(amount);
            return name + " #" + no + ": ₹" + pay + " + GST ₹" + Tax.gst(pay);
        }
    }

    static class Tax {                              // static nested: no stall needed
        static int gst(int amount) { return amount * 5 / 100; }
    }
}

public class Main {
    public static void main(String[] args) {
        Stall s = new Stall("Chai Point");
        Offer diwali = new Offer() {                // anonymous class
            public int apply(int amount) { return amount >= 100 ? amount - 20 : amount; }
        };
        Stall.Bill b1 = s.new Bill(120);
        Stall.Bill b2 = s.new Bill(60);
        System.out.println(b1.print(diwali));
        System.out.println(b2.print(diwali));
    }
}