Interface - Implementation link

[vasanthj]

How does an API know which implementation to use? For example, if I am using the JDBC API in my code, how does the JVM know to call the correct implementation of this API. Let's say I have two driver jars that implement this JDBC API in my classpath. Which one will get called? Is this based on the DriverManager?

[KevinWorkman]

I would recommend providing an example that demonstrates exactly what you're talking about. You might want to use the List interface as an example.

[Tolls]

For JDBC it's the DriverManager.
Each JDBC implementation has a different connection String.
MySQL = jdbc:mysql
Derby = jdbc:derby
Oracle = jdbc:oracle
etc etc.

[vasanthj]

Thanks for the prompt reply. It makes sense now. Can you tell me how this interface-implementation works for JAX-RS -- Jersey? Sorry if i am asking too much.

[Tolls]

Aren't the implementations called something different?
In whatever setup file you define what implementation you are going to use (similar to defining which JDBC driver in your connections string).
Exactly how generally depends on your framework.

[AeneasTroy]

In order to fix this problem, you could ONLY import the required class:

import java.sql.Datasomething;
import com.jdbc.mysql.Driver;

Another way is to instanciate the class with the full class name:

com.jdbc.mysql.Driver myDriver = new com.jdbc.mysql.Driver();

This way, there are no mixups.

Sometimes, old versions and new versions of the same class may exist together. I am not sure how netbeans resolves it.

[Tolls]

What you are thinking of is totally different, and sometimes...
For example, java.sql.* has a lot of the same classes
as for example com.jdbc.mysql.*;

In order to fix this problem, you could ONLY import the required class:
import java.sql.Datasomething;
import com.jdbc.mysql.Driver;

Another way is to instanciate the class with the full class name:

com.jdbc.mysql.Driver myDriver = new com.jdbc.mysql.Driver();
This way, there are no mixups.

Sometimes, old versions and new versions of the same class may exist together. I am not sure how netbeans resolves it.

That's not how you use either of the examples the OP has given.
JDBC does not work like that (you never import the actual Driver you are using, that's the job of the DriverManager or DataSource), and neither do the other similar frameworks (like JAX-RS, or any of the XML stuff).

[AeneasTroy]

I know, I should have left this question alone.
Please disregard my response, I totally didn't understand the question.