SE1.4 VS 1.6

[Robert Richardson]

Hello:

The following compiles and runs using jdk1.6

  
class Name implements Comparable <Name>
{
    public int compareTo(Name n)
    {
        //code
    }
}

class firstNameSort implements Comparator<Name>
{
    public int compare(Name n1, Name n2)
    {
        //code
    }
}
  

But when I modify it to complile using jdk1.4 as below

  
class Name implements Comparable
{
    public int compareTo(Name n)
    {
        //code
    }
}

class firstNameSort implements Comparator
{
    public int compare(Name n1, Name n2)
    {
        //code
    }
}
  

I get two errors Name (or firstnameSort) is not abstract (OK I buy that) and does not override abstract method compare (or compareTo) (looks to me like they do)...

Any tips would be appreciated.

Thanks
Robert Richardson

[Henry Wong]

The types of the parameters to compareTo() and compare() are due to generics. Without generics, they are defined (in Java 1.4) as taking Object type parameters.

Henry

[Robert Richardson]

Henry:
Thanks for your reply. I didn't do a good job asking the question. I can rewrite the code and eliminate the errors I mentioned by changing the reference variable type from Name to Object.

public int compare(Object n1, Object n2)//Object was Name
                 {
                     String fn1 = (Name)n1.getFirstName();
                     String fn2 =  (Name)n2.getFirstName();
                     return (fn1.compareTo( fn2));
                 }
   

I want to cast the Object to Name so I can use its methods but the complier still thinks n1 and n2 are Objects not Names.
I'm sure I'm missing something fundamental but it escapes me.
Thanks for yor help.
Robert

[Steve Luke]

Your casting incorrectly. The dot operator has precedence over the cast, so you have to modify the order to ensure you cast first, then call the method on the casted reference. Do it using parenthesis:

String fn1 = ((Name)n1).getFirstName();

[Robert Richardson]

My worst fears have been realized. My problem was trivial. Oh well! Nothing to do but press on.
Thanks to you guys for your help.
Robert

[Nitish Bangera]

I get two errors Name (or firstnameSort) is not abstract (OK I buy that) and does not override abstract method compare (or compareTo) (looks to me like they do)...

This error is basically given when the compiler finds that you are not fulfilling the contract of the interface(concrete classes should implement all methods of the interface). May be a quick look at the java1.4 api docs would have solved the problem there and then.