Creating and using exceptions

[Janam Robby]

Creating exceptions and passing them to the controlling module (here method with scenarios). After an exception occurs your code should stop execution of current scenario and go to another one.

You could for example create MoviePropertiesNotSetException, IllegalAgeException, etc.

You need to have several scenarios resulting with different exceptions being thrown before finally executing a final scenario without exceptions being thrown.

My code is as below:

import java.util.*;
public class Cinema 
{
    float cost;
    String Title;
 
    String mrPG="PG";
    String mrA="A";
    String mrG="G";
      
    Movie movieNew = new Movie();
    
     //MovieRating class
    MovieRating mrating = new MovieRating();
    private ArrayList<Human> hm = new ArrayList();
    
    public Cinema()
    {
        
    }
    public Cinema (String mtitle, float pounds) 
    {
            this.Title=mtitle;
            this.cost = pounds;
    }
 
    public float getcost (int people) 
    {
        return cost * people;
    }
       
    /**
    * Method check that the movie title and rating have been set,
    * if not throw an exception.
    */
    public  void setMovie(Movie movieNew) throws MyException
    { 
        if(movieNew.getTitle()!=null && movieNew.getRating()!=null)
        {
             System.out.println("The movie is called " +movieNew.getTitle()+ 
                    " and is rated " +movieNew.getRating()+ ".");
        }
        else
        {
            throw new MyException("The Movie properties not set");
        }
    }
     /*
      * this method first checks if the movie properties are set.
      */
    public void showMovie() throws MyException
    { 
//        movieNew.setName("Comedy");
//        movieNew.setRating("PG");
//        movieNew.setTitle("Mr Bin");
        if(movieNew.getTitle()!=null || movieNew.getRating()!=null)
        {
             System.out.println("Now Showing... "+movieNew.getTitle());             
        }
        else
        {
            throw new MyException ("The  movie properties are not set.");
        }            
    }
     /*Checks if Movie properties are set, if not throws MyException
      * takes a collection of Human - Adult and Child
      */ 
    public void addMovieGoers(Human h) throws MyException
    {
        Human a = new Adult("Joe",43);
        Human b = new Adult("Sue",39);
        Human c = new Adult("Tracy",20);
        Human d = new Child("Sammy",17);
        Human e = new Child("Julie",12);
        Human f = new Child("Mona",6);
        hm.add(a);hm.add(b);hm.add(c);hm.add(d);
        hm.add(e);hm.add(f);
 
        hm.trimToSize();
        String toPrint = "";
 
        if(movieNew.getRating()!=null && movieNew.getTitle()!=null)
        {
             if(mrPG.equals(movieNew.getRating())) //movies rated PG
             {                        
                System.out.println("The following can only watch under parental guidance:");
                for(int i = 0; i < hm.size(); i++)
                {
                    Human test = (Human)hm.get(i);
                    if ( test instanceof Child)
                    {
                        if(toPrint.equals("")) 
                        {
                            System.out.println(test);  
                        }
                        else
                        {
                             System.out.println("Children: " + toPrint);
                        }
                     }
                 }
            }
            else if(mrA.equals(movieNew.getRating())) //movies rated Adult
            {
                System.out.println("The following can watch...");
                for ( int i = 0; i < hm.size(); i++)
                {
                    Human test = (Human)hm.get(i);
                    if ( test instanceof Adult)
                    {
                        if(toPrint.equals("")) 
                        {
                            System.out.println(test);  
                        }
                        else
                        {
                             System.out.println("Adults: " + toPrint);
                        }
                    }
                                 
                } 
            }
            else //Movies rated G
            {                        
                System.out.println("This is movie rated G. So the following can watch"+
                        ": "+hm+"");
            }
        }
        else
        {
            throw new MyException("The Movie properties are not set.");
        } 
    }
 
    public static void main(String args[]) throws MyException
    { 
        Cinema cn = new Cinema();
        Human h = new Human();
        //instantiating and setting properties to the movie 
        Movie movieNew = new Movie();
        movieNew.setName("Comedy");
        movieNew.setRating("PG");
        movieNew.setTitle("Mr Bin");
        try
        {
            if(movieNew.getRating()!=null && movieNew.getTitle()!=null)
            {
                cn.showMovie();
                
            }
        }
        catch(MyException exp)
        {
            System.out.println("Nothing");
        }
 
    }
}
 

NOTE: Finally add another static method to the cinema class that demonstrates the usage of the cinema class. Include multiple scenarios to show how the exceptions work.

[Joanne Neal]

Did you have a question ?

[Campbell Ritchie]

Probably best to create a CinemaException and use it as a superclass for all other Exceptions. It is very easy to create your own Exceptions; in 99% of cases you only need to create 4 constructors, as in the Exception class itself. You can decide whether it is checked or unchecked by correctly choosing the superclass for CinemaExpression.