This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
In Java, the choice of which method of the interface will be invoked is determined at compile time. However, the choice of on which class to invoke this method can only be determined at runtime. Furthermore, once you know which class, the JVM must still load the class which is another delay in the binding. Java is late binding.