Unchecked or unsafe operations warning

Hi everyone,

When I compile my code, the compiler returns that it has unsafe or uncheck operations. Then, I re-compile it with the option -Xlint:unchecked, and I get all this warnings:

Code:

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javac -Xlint:unchecked ExecuteCommand.java
ExecuteCommand.java:16: warning: [unchecked] unchecked conversion           
found  : java.util.ArrayList                                               
required: java.util.ArrayList<Cinema>                                       
    private ArrayList<Cinema> cinemas = new ArrayList();                   
                                        ^                                   
ExecuteCommand.java:17: warning: [unchecked] unchecked conversion           
found  : java.util.ArrayList                                               
required: java.util.ArrayList<Film>                                         
    private ArrayList<Film> films = new ArrayList();                       
                                    ^                                       
ExecuteCommand.java:18: warning: [unchecked] unchecked conversion           
found  : java.util.ArrayList                                               
required: java.util.ArrayList<Booking>                                     
    private ArrayList<Booking> bookings = new ArrayList();                 
                                          ^                                 
ExecuteCommand.java:270: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
                            outputArray.add(getNameOfDay(j));                                                       
                                          ^                                                                         
ExecuteCommand.java:309: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
                    outputArray.add(cinema.getName());                                                               
                                  ^                                                                                 
ExecuteCommand.java:348: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
            output.add(bookingID);                                                                                   
                      ^                                                                                             
ExecuteCommand.java:367: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
            output.add(booking.getFilmName());                                                                       
                      ^                                                                                             
ExecuteCommand.java:368: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
            output.add(booking.getCinemaName());                                                                     
                      ^
ExecuteCommand.java:369: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
            output.add(getNameOfDay(booking.getDay()));
                      ^
ExecuteCommand.java:370: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
            output.add(booking.getSeats());
                      ^
10 warnings

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Any idea about what is happening with my code? Thanks in advance.

Code:

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found  : java.util.ArrayList                                               
required: java.util.ArrayList<Cinema>                                       
    private ArrayList<Cinema> cinemas = new ArrayList();

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The error message means what it says. You had written

Code:

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private ArrayList<Cinema> cinemas = new ArrayList();

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but the compiler saw that you had declared cinemas as ArrayList<Cinema> and, so, expected you to call the appropriate constructor:

Code:

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private ArrayList<Cinema> cinemas = new ArrayList<Cinema>();

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The original warning was just that: a warning. You can ignore it if you want but it is considered a bad programming practice to use the raw type (ArrayList without the <Cinema>) unless you need to because you are using methods from older (nongeneric) libraries.

See Type Erasure (The Java™ Tutorials > Learning the Java Language > Generics) (and possibly more of the surrounding chapter on generics.)

Ok, I've already fixed the three first warnings (indeed I should read more carefully the warnings, but I didn't know that kind of constructor exists). Now I'm going to read the link to see if I can fix the other ones. I appreciate the help and thanks for the link.

Again I think it's that outputArray and output have been (declared and) initialised as ArrayList rather than ArrayList<String> or whatever they are supposed to be array lists of.