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From: Jason S <jason.savlov@gmail.com>
Newsgroups: comp.lang.java.programmer
Date: Wed, 20 Apr 2011 13:53:55 -0400
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Thank you! I understand how that works now. Except it still outputs 
0.000 for the cat's weight. Everything else works though.

On 2011-04-19 14:03:03 -0400, Lew said:

> Jason S wrote:
>> http://web.cs.sunyit.edu/~savlovj/CS249/pg472_8
>> 
>> The code is there in full
> 
> 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 );
>    }
> 
> }
> 
> ============================================================


-- 
Jason