Re: Double always returning 0.0

Jason S wrote:


There are a few things you should watch out for in your code.

Stylistically, in a class declaration you should list all fields first, then
constructors, then methods. (You haven't learned about 'static' members yet,
so I do not speak of those at this time.) This makes it easier to find what
you're looking for.

You declare the same exact attributes in supertype and subtype:

  public class Pet {
    private String name;
    private int age; // years
    private double weight; // lbs
   ...

  public class Cat extends Pet {
    private String name;
    private int age;
    private double weight;
   ...

This is bad. Because 'Cat' /is-a/ 'Pet', it already possesses within itself
these attributes already, without redeclaring them. The only question is how
it can gain access to them. As it is, you call 'setAge()' on a 'Cat' and it
will fail to do what you expect. Plus, the type's clients have no way to read
the attributes.

The answer (one answer) is to add accessor ("getter") and mutator ("setter")
methods for each attribute. (No setter is needed for read-only attributes.)
I added exceptions and a couple of 'this()' constructor references for your
study fun. Note that your individual constructors only work because the
argument types differ. That's a power trick you used there.

You should use 0.0 for a double constant, not 0.

I have omitted Javadocs for this example, but that's a bad habit.

As someone else suggested, the dosage methods should be abstract in the parent
type.

============================================================

  public abstract class Pet {
    private String name;
    private int age; // years
    private double weight; // lbs

   public Pet( String name, int age, double weight ) {
     setName( name ); // works because the setters are final
     setAge( age );
     setWeight( weight );
   }

   public Pet( String name ) {
     this( name, 0, 0.0 );
   }

   public Pet( int age ) {
     this( "", age, 0.0 );
   }

   public Pet( double weight ) {
     this( "", 0, weight );
   }

   public Pet()
     this( "", 0, 0.0 );
   }

   public final String getName() (
     return this.name;
   }
   public final void setName( String name ) {
     if ( name == null ) {
       final String msg = "null name.";
       throw new IllegalArgumentException( msg );
     }
     this.name = name;
   }

   public final String getAge() (
     return this.age;
   }
   public final void setAge( int age ) {
     if ( age < 0) {
       final String msg = "negative age "+ age +".";
       throw new IllegalArgumentException( msg );
     }
     this.age = age;
   }

   public final String getWeight(() (
     return this.weight;
   }
   public final void setWeight( double weight ) {
     if ( weight < 0.0 ) {
       final String msg = "negative weight "+ weight +".";
       throw new IllegalArgumentException( msg );
     }
     this.weight = weight;
   }

   public abstract double acepromazine();
   public abstract double carprofen();

  }

============================================================

  public class Cat extends Pet {

   public Cat( String name, int age, double weight ) {
     super( name, age, weight );
   }

   public Cat( String name ) {
     super( name );
   }

   public Cat( int age ) {
     super( age );
   }

   public Cat( double weight ) {
     super( weight );
   }

   public Cat()
   }

   @Override
   public double acepromazine() {
     return (weight * 0.002 / 10.0 / 2.2 );
   }

   @Override
   public double carprofen() {
     return ( weight * 0.25 / 12.0 / 2.2 );
   }

}

============================================================

--
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg