Empty constructor in FeedReaderContract demo

Referring to the FeedReaderContract class on Android Developers page:

• Saving Data in SQL Databases

The code starts as:

public final class FeedReaderContract {
    // To prevent someone from accidentally instantiating the contract class,
    // give it an empty constructor.
    public FeedReaderContract() {}

i.e. there is a default public constructor for the class.

• Is that code comment correct?
• How does a public empty constructor prevent instantiation - should this maybe be private?

... am I still half asleep ? ...

PS I'm not concerned about the rest of the example, or how to use it. I am purely trying to confirm that I'm not going mad and stupid at the same time...