Description
Objectives
Creating a hierarchy of classes
Further understanding of inheritance
Introduction
This laboratory consists of creating a hierarchy of classes for representing documents. The hierarchy of
documents consists of a superclass called Document. All the Documents have a name, an owner and an
index number. The class Document is specialized into MediaDocument. All MediaDocuments have a
duration. The calculation of the rating of a document depends on the specific type of MediaDocument,
namely Movie or Audio. Therefore, the implementation of the method getRating() is done in the classes
Movie and Audio. The implementation of the classes must follow the principles of encapsulation presented
in class.
1 Document
Implement a concrete class, called Document, to represent the characteristics that are common to all the
documents. Namely,
1. All documents must have a unique identifier (of type int). The first document created will have the id
100, the id of the next one will be 101, and so on. A newly created object has a unique id which is one
(1) more than the id of the last object that was created;
2. All documents have a name and an owner (both of type String);
3. The class Document has one constructor. Its signature is as follows: Document( String name, String
owner ). The constructor must initialise the name and owner of the document using the given
parameters, as well as initialising the unique identifier of this Document;
4. public int getIndexNumber(): returns the unique identifier, here called index number, of this
document;
5. public String getName(); returns the name of this document;
6. public void rename( String name ): changes the name of the document to name;
7. public String getOwner(): returns the owner of this document;
8. public void changeOwner( String owner ): changes the owner of the document to owner;
9. public boolean equals( Document other ): returns true if other designates a document, and that
document has the same index number (unique identifier);
10. public String toString(): returns a String representation of this Document, consisting of the index
number, document name and owner.
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Files
Document.java
2 MediaDocument
Implement a class, called MediaDocument, to represent the characteristics that are common to all the media
documents. All the media documents have a method int getRating(), however the implementation of the
method is specific to the kind of document.
1. A MediaDocument is a specialised kind of Document. Therefore, it must be a subclass of Document;
2. All media documents have a duration (of type int);
3. The class MediaDocument has a single constructor. Its signature is as follows: public
MediaDocument( String name, String owner, int duration ). It initialises the characteristics that are
common to all Documents, as well as the duration.
Files
Document.java
MadiaDocument.java
3 Movie
A Movie is a specialised MediaDocument that also has information about the rating of the story and acting.
More precisely,
1. A Movie is a (concrete) subclass of MediaDocument;
2. It also stores information about the rating of the story and the acting (both of type int). This
information (two numbers in the range 1 …10) is given as an argument to the constructor;
3. It has a single constructor and here is its signature: public Movie( String name, String owner, int
duration, int story, int acting ). It serves to initialise all the characteristics that are common to all
media documents, as well as the story and acting ratings. You can assume that the numbers, ratings, are
valid;
4. public int getStoryRating(): returns the story rating;
5. public int getActingRating(): returns the acting rating;
6. It implements the method public int getRating(), which returns the average of the story and acting
ratings rounded to the nearest integer.
Files
Document.java
MadiaDocument.java
Movie.java
4 Audio
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Audio is a specialised MediaDocument that also has information about the rating of this Audio document.
More precisely,
1. Audio is a (concrete) subclass of MediaDocument;
2. It stores the rating (an int) of this document. The rating of an Audio document is a single number, the
overall appreciation of the piece;
3. It has a single constructor. Its signature is: public Audio( String name, String owner, int duration,
int rating ). It initialises the properties that are common to all media documents, as well as the rating
of this document;
4. It implements the method public int getRating(), which returns the rating of this document. In the case
of an Audio document, the rating is a single number, therefore, the method simply returns this number.
In a “real-world” application, the documents would contains additional attributes and methods (at least
some content!). However, in the context of this laboratory, we will limit ourselves to those attributes and
methods.
5 Test
Create a test program. In the main method, declare an array to store MediaDocument objects. Fill the array
with Movie and Audio documents. Finally, write a loop that caclcutes the sum of all the ratings.
Files
Document.java
MadiaDocument.java
Movie.java
Audio.java
Test.java
6 Quiz (1 mark)
To invoke a parents constructor in a subclass, we use the __________________________________
method.
1. abstract
2. construct
3. parent
4. super
5. extends
Answer:
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