Objektorienteeritud programmeerimine (Narva Kolledž) 2019/20 kevad

Session 6

Tasks

Task 1. A nice day in the amusement park (study the code)

The director of the amusement park has signed a contract with you to develop a piece of software for his park. The software has to check children's age. In the amusement park, only 12+ years old teenagers can take a ride. To check the age, teenagers have to show a document. Usually, teenagers bring ID cards or students cards with them. To speed up the process, the documents are checked in bulk.

public class IdCard {
  private String idNumber;

  public IdCard(String idNumber) {
    this.idNumber = idNumber;
  }

  public boolean isAtLeast12YearsOld() {
    int currentYear = LocalDate.now().getYear();
    return birthYear() <= currentYear - 12;
  }

  private int birthYear() { 
    int firstDigit = Integer.parseInt(idNumber.substring(0, 1));
    int bYear = Integer.parseInt(idNumber.substring(1, 3));
    if (firstDigit <= 2)
      return 1800 + bYear;
    if (firstDigit <= 4)
      return 1900 + bYear;
    if (firstDigit <= 6)
      return 2000 + bYear;
    return 2100 + bYear;
  }
}

public class StudentCard {
  private int birthYear;

  public StudentCard(int birthYear) {
    this.birthYear = birthYear;
  }

  public boolean isAtLeast12YearsOld() {
    return birthYear + 12 <= LocalDate.now().getYear();
  }
}

public class RussianMountains {

  public boolean ageControlOK(IdCard[] idCards, StudentCard[] studentCards) {
    for (IdCard id : idCards) {
      if (!id.isAtLeast12YearsOld())
        return false;
    }

    for (StudentCard card : studentCards) {
      if (!card.isAtLeast12YearsOld())
        return false;
    }
    return true;
  }
}

Read about the LocalDate class here and here.

In a week, the director of the amusement park contacts you again and says that some people bring driving license with them. Therefore, some changes must be done in the program.

If we have a look at the ageControlOK method in the class RussianMountains, then it is easy to change so that the method would take in all objects that have an instance method isAtLeast12YearsOld. Let us create an interface for this method:

public interface Document {
  boolean isAtLeast12YearsOld();
}

Change the RussianMountains class as follows:

public class RussianMountains {

  public boolean ageControlOK(Document[] documents) {
    for (Document doc : documents) {
      if (!doc.isAtLeast12YearsOld())
        return false;
    }
    return true;
  }
}

Furthermore, the classes IdCard and StudentCard have to implement the interface:

public class IdCard implements Document {
  // the rest code is not changed
}

public class StudentCard implements Document {
  // the rest code is not changed
}

public class Test {
  public static void main(String[] args) {

    RussianMountains mountain1 = new RussianMountains();//create a ride

    //create a bulk of different documents and assign to a variable to interface Document data type
    Document[] documents = { 
        new IdCard("39108071234"),
        new StudentCard(1991)
    }; 

    //check if all visitors can take a ride and print the result
    System.out.println("is age OK?: " + mountain1.ageControlOK(documents));
  }
}

Task 2. Return the documents (modify the previous code)

If a person has not passed the age control, the document has to be returned to the person. In the RussianMountain class, create a method called ageControlFail. The method takes in an array of documents and returns the list documents (List<Document>) that fail the age control.

In the main method, print all the documents that failed the age control. Make sure that the output is readable (add a method called toString into classes IdCard and StudentCard).

Hint. List is an interface. That means it is not possible to create objects of this type. ArrayList implements all the methods of List and we can create objects of that class. Do not forget about a generic data type: ArrayList<Document>.

Task 3. Ferris wheel

The amusement park has decided to open a new ride - Ferris wheel. The age restriction is 14 on this ride (the ride might be dangerous to small kids). In the Document interface, delete the isAtLeast12YearsOld method and replace it with a new method - isAtLeastXYearsOld. The latter method should check if the person is at least x years old (x is a parameter).

Change classes IdCard and StudentCard so that they would implement the changes of the interface.

The RussianMontain class must become more general. Therefore, rename the class to AmusementRide (in IntelliJ: Refactor -> Rename). In the class, add private instance fields for the ride name (String) and the minimum age when a person is allowed to take a ride on it (int). Also add a constructor and the toString method. Do not forget to change some signatures.

Create a new test class called Test2. In its main method, create at least two amusement rides (one has at least 14 years old restriction, and the other one has at least 12 years old restriction). Also create an array with at least two documents (a student card whose holder is 13 years old and ID card whose holder is 15 years old). Print out information about each person if they can take a ride on each amusement ride.

Task 4. Fortune's wheel

The sales manager of the amusement park has decided to raffle off some special gifts among the most active visitors of the park. Write a program which returns a list of the most active visitors and chooses the winner out of them. In the final raffle off, only three visitors participate.

First of all, create Visitor class which has a private instance field for visitor's name (String) and a private instance field which keeps the number of rides (int) made in the park. Add a constructor which instantiates all the instance fields. Also add the get methods and the toString method. The latter has to show visitor's name.

Create a class called FortuneWheel. Create a private instance field which holds a list of visitors in an appropriate data structure. Using the overloading, create two versions of method addVisitor: 1. the method takes in objects of the class Visitor; 2. the method takes in two parameters: the name of a visitor and the number of rides the visitor has taken in the park.

In the class, also add the theMostActive(int n) method. The method has to return n the most active visitors out of the list (or the whole list if n is larger than the size of the list). The most easier way to do that is to sort the list by the number of rides. We can use the method sort of java.util.Collections class. However, the sort method needs some help from us. In Visitor class, we have to explain Java what and how exactly we want to compare (check the example at the end of the page). Also pay attention to the fact that the parameter of the Collections.sort method is the List interface. Since ArrayList implements the interface, we can use it as a parameter.

The method winnerOfLottery does not have parameters and returns one out of the three the most active visitors (Hint: use method Math.random).

Create a test class Test3. In its main method create a Fortune's wheel and at least 5 visitors. Register the visitors to the lottery, test the fortune's wheel methods and print winner's name.

Session 6