Question

private static ThreadLocal<Connection> connectionHolder = new ThreadLocal<Connection>() {
    public Connection initialValue() { 
         return DriverManager.getConnection(DB_URL);
    }
};

I don’t understand what’s going on in the part that’s within the stars. Is that a way to insert a method into a class?

Answer 1

The initialValue() method of ThreadLocal is just a way to construct a ThreadLocal holding a value other than null.

Edit: Oh, I see that’s not what you’re asking about. What you have there is the same as if you did:

public class MyOwnThreadLocal extends ThreadLocal {
    public Connection initialValue() {
        return DriverManager.getConnection(DB_URL);
    }
}

Except your version doesn’t require a completely separate class definition–hence it’s called an “anonymous class”.