Is Programming the Art of Making the Right Decision?

If you’ve read my previous blog on using Explicit Locking, you may remember that I wrote some sample code that transferred cash between two random bank accounts using the following algorithm:

IF fromAccount is locked THEN
    IF toAccount is locked THEN
        withDraw money from the fromAccount
        deposit money into the toAccount
    END IF
END IF

You may also remember that this was multithreaded code originally written to create a deadlock. In order to demonstrate Explicit Locking’s Lock interface and ReentrantLock implementation I needed to add a thread locking mechanism to my straight-forward Account POJO and so, the question was: how should I do this?

Implementing the Observer Pattern using Composition

When I previously discussed the Observer pattern I recommended following Joshua Bloch’s advice and “favor composition over inheritance” and suggested that the JDK’s implementation of the Observer, Observable, though convenient, was somewhat flawed. This blog demonstrates how to implement the Observer pattern using composition. The benefit of using this technique is that it clearly upholds the single responsibility principle broken in several places by my earlier news server examples.

UML, Aggregation and Java

One problem you often see when dealing with UML is that some developers don’t get the idea that what you see in class diagram should translate directly into code they draw a class diagram and write some code and neither bare any resemblance to each other. This, and other blog forthcoming blogs in the series, demonstrate the link between diagrams and code.