Java programming language

Object oriented programming

Classes and objects in Java - Additional exercises

  

Exercise 1

Create a project named Stores, and implement the following classes:

• An abstract class called Store. It will have an abstract method called welcome, two private fields (cash and drinkPrice, both double) and a constructor that will receive the drinkPrice and initialize cash to 0.0. It will also implement a method called payDrinks(int numOfDrinks) that will add to the cash variable the payment (number of drinks * price).
• A class called LiquorStore that will extend Store class. It will implement the welcome method to show the message “Welcome to the liquor store”, and it will have a new private field called tax (an integer). Its constructor will receive the drinkPrice and tax values, calling the parent’s constructor when necessary. This class will also override payDrinks(int) calling first the parent’s method (pay without tax), and then adding the tax value to the cash field.
• A Main class with the main method. This method will:
  • Create a LiquorStore object with drinkPrice = 8.95€ and tax = 20%. Pay for 10 drinks and print the cash to see if its value is 107.40€ (print 2 decimal numbers).
  • Instantiate a Store using an anonymous class. The drink price will be 8.95€ and the welcome method will say “Welcome to anonymous store! Our drink price is XX€” (where XX will be the value of drinkPrice attribute, with 2 decimals). Call the welcome method and also pay for 10 drinks. Show the resulting cash (should be 89.50€).
• Implement getters and setters when needed

Exercise 2

Create a project named KillEnemies, and implement the following classes:

• Interface Character: With a method called isEnemy() that returns a boolean.
• Class Friend: Implements Character. isEnemy() returns false.
• Class Enemy: Implements Character. isEnemy() returns true. Also implements a method called kill() that shows this message: “Ahhhggg, you killed me, bastard!”.
• Class Main containing the main method. You must create a list (ArrayList) of 10 Character objects (5 friends and 5 enemies), then, using Collections.shuffle(List), randomize the order of the items. You have to travel through all characters checking if they are enemies, and if they are, you kill them (call kill() method).

An example of execution message would be:

Character 0 is a friend! :-)
Character 1 is a friend! :-)
Character 2 is an enemy! kill it!
Ahhhggg, you killed me, bastard!
...