Because the class Video
does not define the instance variables
director
and rating
,
so its toString()
method can't use them.
We need a new toString()
method in the class Movie
:
// added to class Movie public String toString() { return title + ", " + length + " min. available:" + avail + " dir: " + director + ", rating: " + rating ; }
Now, even though the parent has a toString()
method,
the new definition of toString()
in the child class will override
the parent's version.
A child's method overrides a parent's method when it has the same signature as a parent method. Now the parent has its method, and the child has its own method with the same signature. (Remember that the signature of a method is the name of the method and its parameter list.)
An object of the parent type includes the method given in the parent's definition. An object of the child type includes the method given in the child's definition.
With the change in the class Movie
the
following program will print out the full information for both items.
class VideoStore { public static void main ( String args[] ) { Video item1 = new Video("Microcosmos", 90 ); Movie item2 = new Movie("Jaws", 120, "Spielberg", "PG" ); System.out.println( item1.toString() ); System.out.println( item2.toString() ); } }
The line item1.toString()
calls the toString()
method
defined in Video
, and
the line item2.toString()
calls the toString()
method
defined in Movie
.
Microcosmos, 90 min. available:true Jaws, 120 min. available:true dir: Spielberg PG, rating: PG
Does the definition of toString()
in the Movie
class
include some code that is already written?