JRuby is an implementation of the Ruby programming language atop the Java Virtual Machine, written largely in Java. JRuby is tightly integrated with Java to allow the embedding of the interpreter into any Java application with full two-way access between the Java and the Ruby code.
Robert C.Martin wrote an interesting article about a set of metrics that can be used to measure the quality of an object-oriented design in terms of the interdependence between the subsystems of that design.
Here’s from the article what he said about the interdependence between modules:
What is it that makes a design rigid, fragile and difficult to reuse. It is the interdependence of the subsystems within that design. A design is rigid if it cannot be easily changed. Such rigidity is due to the fact that a single change to heavily interdependent software begins a cascade of changes in dependent modules. When the extent of that cascade of change cannot be predicted by the designers or maintainers the impact of the change cannot be estimated. This makes the cost of the change impossible to estimate. Managers, faced with such unpredictability, become reluctant to authorize changes. Thus the design becomes rigid.
C# introduced the internal keyword to enables information hiding across program boundaries. It can improve the ease of maintenance on much larger programs. When a public class is declared as internal, it’s accessible from the assembly containing this class, but hidden from any other assembly using it.
Java doesn’t have an equivalent of the internal keyword, and not provides any solution out of the box to have the same behavior.
Hibernate is an open source Java persistence framework project. Perform powerful object relational mapping and query databases using HQL and SQL.
In general the widely used libraries are well designed and implemented, and it’s very interesting to learn from them some coding best practices. Let’s take a look inside the hibernate core library and discover some of its design keys.
In this post Hibernate Core is analyzed by JArchitect to go deep inside its design and implementation.
Groovy is an object-oriented programming language for the Java platform. It is a dynamic language with features similar to those of Python, Ruby, Perl, and Smalltalk. It can be used as a scripting language for the Java Platform, is dynamically compiled to Java Virtual Machine (JVM) bytecode, and interoperates with other Java code and libraries.
Let’s go inside Groovy to discover how it works internally, for that we use JArchitect.
Groovy comes with many libraries like groovy-sql, groovy-json and others, here’s the dependency structure matrix of all groovy jars.
There is a powerful and simple concept in programming that is really underused: Immutability.
Basically, an object is immutable if its state doesn’t change once the object has been created. Consequently, a class is immutable if its instances are immutable.
There is one killer argument for using immutable objects: It dramatically simplifies concurrent programming. Think about it, why does writing proper multithreaded programming is a hard task? Because it is hard to synchronize threads accesses to resources (objects or others OS things). Why it is hard to synchronize these accesses? Because it is hard to guarantee that there won’t be race conditions between the multiple write accesses and read accesses done by multiple threads on multiple objects. What if there are no more write accesses? In other words, what if the state of the objects threads are accessing, doesn’t change? There is no more need for synchronization!
Java 6 was released in 2006 and Java 7 in 2011. No major changes were added to the Java7, many of the new features were present in Java 6 updates. After Java 7 Oracle has decided to implement a two years roadmap planning for Java, and the next major release will be available in 2013.
Java 8 has some interesting new features like lambda expressions, but the major new feature planned was Jigsaw, in fact Jigsaw was originally intended for Java 7 but was deferred to Java 8 and now it’s moved to Java 9.