Java .This laboratory consists of creating a hierarchy of classes for representi

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Java .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 (id). 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. Q1. 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, id, (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. 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. Q2. MediaDocument ( an abstract class) 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. Q3. 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. Q4. Audio 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,a s 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 eal-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. Q5. 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 calculates the sum of all the ratings. Additional exercise: Implement a method int getRating() in the class Document that always returns a 0. In your Test program, create different reference variables of different classes and assign them to objects of different classes (documents, Movie,etc). Use these references to call the method getRating(). Verify in each case which method is called (using which class).

Explanation / Answer

class Document
{
   public static int id=100; // define a static for first document value as 100
   public String name, owner
   Document(String name, String owner)
   {  
       this.name=name;
       this.onwer=owner;
       id=id+1; //increment 1 for next id of next document
   }
   public int getIndexNumber()
   {
       return (id);
   }
   public String getName()
   {
       return(name);
   }
   public void rename(String n)
   {
       name=n;
   }
   public void changeOwner( String own )
   {
       owner =own;  
   }
   public boolean equals( Document other )
   {
       if(this.id==other.id)
           return (true);
       else
           return (false);
   }
   public String toString()
   {
       String rec = this.id+"- "+ this.name+ "- "+this.owner; //concatenate values as a single record
       return rec;      
   }
}

public abstract class MediaDocument extends Document
{
   public int duration;
   public abstract int getRating();
   public MediaDocument( String name, String owner, int duration )
   {
       super(name,owner);      
       this.duration=duration;  
   }
}
public class Movie extends MediaDocument
{
   int story, acting;
   public Movie( String name, String owner, int duration, int story, int acting )
   {
       super(name,owner,duration);
       this.story=story;
       this.acting=acting;
   }
   public int getRating()
   {
       float avg;
       int res;
       avg=(story+acting)/2;
       res = (int ) Math.round(avg);
       return (res);
   }
}
public class Audio extends MediaDocument
{
   int rating;
   public Audio( String name, String owner, int duration, int rating )
   {
       super(name,owner,duration);
       this.rating=rating;
   }
   public int getRating()
   {
       return(rating);
   }
}
public class Test
{
   public static void main(String args[])
   {
       MediaDocument obj =new MediaDocument[10];
   }
}

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