Practice: Example

Which keyword does a class use to adopt an interface, and which keyword does one interface use to inherit another interface?

In the interface interface Data { double PI = 3.142; double volume(); }, what modifiers does the compiler add to PI and to volume()?

Which declaration correctly makes Dog a subclass of Animal that also implements the interface Pet?

Which modifiers does Java automatically give to a field declared in an interface, such as double PI = 3.142?

An interface Conveyance has a constant FUEL_PRICE = 100.0 (rupees per litre, an assumed price) and a method double fuelCost(double km). A Bike runs 50 km on one litre and a Car runs 15 km on one litre. Write classes Bike and Car that implement Conveyance, and print the fuel cost of a 300 km trip for each, using an array of type Conveyance[].

A school library allows 14 days for every item. Write an interface Borrowable with the constant MAX_DAYS = 14 and a method double fine(int daysLate). A Book is fined Rs 2 per late day; a Magazine is fined Rs 1 per late day but never more than Rs 10. Write a method static double totalFine(Borrowable[] items, int[] daysKept) and use it for a book kept 19 days, a magazine kept 29 days and a book kept 10 days.