Interface problems...

[Marcus Laubli]

I'm writing some code to handle user preferences. To do this, I wrote the following Node.java file:

 
package com.foursight.preferences;
 
import java.io.* ;
import java.util.prefs.* ;
import java.util.prefs.NodeChangeListener ;
import java.util.prefs.NodeChangeEvent ;
import java.io.FileOutputStream ;
 
public abstract class Node
{
    // TODO check parameters too!
 
...
}
 

Then, I created the following Registry.java file...

package com.foursight.preferences;
 
import java.io.* ;
import java.util.prefs.* ;
import java.io.FileOutputStream ;
 
 
Line 8 public class Registry implements Node
{
    protected Preferences node ;
    private boolean hasNCL ;
    private boolean flushed ;
    
    public Registry ( String type, Class nodeName )
    {
       ...
 
 

I'm really trying to use an interface correctly. However, on line 8, my IDE is giving me the following error: "Interface expected here". What's going on? As soon as I typed implements Node, the IDE offered to populate all of my method headers.

I'm confused.
[ April 15, 2005: Message edited by: Marcus Laubli ]

[Henry Wong]

Node is an abstract class, not an interface.

Henry

[Marcus Laubli]

I admit, this is the part that I was weakest on in my exam!

So all I have to do is change it to:

public interface Node?
[ April 15, 2005: Message edited by: Marcus Laubli ]

[miguel lisboa]

sure, why dont you try it?

[Marcus Laubli]

I tried, but Studio Creator still shows the error. It's confusing.

[Henry Wong]

Originally posted by Marcus Laubli:
I admit, this is the part that I was weakest on in my exam!

So all I have to do is change it to:

public interface Node?

That depends on whether is it an interface or an abstract class.

If it is just interface definitions then sure. If it is an abstract class, then extending from it is probably easiest.

BTW, for either case, your IDE should complain and offer to generate stubs for all the methods -- at least the good ones, anyway.

Henry

[Marcus Laubli]

Thanks for the help.

The error went away. I'm dealing with other things now. I think I can manage.

[miguel lisboa]

of course you need to declare at least one method in your interface:

public SomeType myMethod1();

[satyendra adhikari]

"of course you need to declare at least one method in your interface:"


not at all, you can have all empty interface, also called marker interface.

[Marcus Laubli]

Thanks Guys!

It finally went up. It's taken so long, but this exercise made it click. Now I understand...

What I really want is:

public abstract class Registry implements Node

I'll put the rest of my abstract method definitions into here for the registry specific things, then create SystemNode.java and UserNode.java to finish the job.

Man, Java really is cool! "I love it when a plan comes together!"

[miguel lisboa]

thanks, satyendra

its quite well explained here