The name reflection is used to describe code which is able to inspect other code in the same system (or itself).
For example, say you have an object of an unknown type in Java, and you would like to call a 'doSomething' method on it if one exists. Java's static typing system isn't really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called 'doSomething' and then call it if you want to.
So, to give you a code example of this in Java (imagine the object in question is foo) :
Method method = foo.getClass().getMethod("doSomething", null);
method.invoke(foo, null);
One very common use case in Java is the usage with annotations. JUnit 4, for example, will use reflection to look through your classes for methods tagged with the @Test annotation, and will then call them when running the unit test.
There are some good reflection examples to get you started at http://docs.oracle.com/javase/tutorial/reflect/index.html
And finally, yes, the concepts are pretty much similar in other statically typed languages which support reflection (like C#). In dynamically typed languages, the use case described above is less necessary (since the compiler will allow any method to be called on any object, failing at runtime if it does not exist), but the second case of looking for methods which are marked or work in a certain way is still common.
Update from a comment:
The ability to inspect the code in the system and see object types is
not reflection, but rather Type Introspection. Reflection is then the
ability to make modifications at runtime by making use of
introspection. The distinction is necessary here as some languages
support introspection, but do not support reflection. One such example
is C++
There are several differences between HashMap and Hashtable in Java:
Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.
Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.
Best Answer
Just to clarify how Drools Flow supports the requirements you are describing (refering to the Drools Flow documentation):
Drools Flow uses (domain-specific) work items (Chapter 8) to interact with external systems. These could be automated services, or a human task management component (Chapter 9) for manual tasks. This human task component is fully pluggable but Drools Flow supports a WS-HumanTask implementation out of the box. Drools 5.1 will include web-based task lists, including custom task forms.
The engine allows you to start processes that can live for a long time. The process supports different kinds of wait states (work item nodes, event nodes, event wait nodes, sub-process, etc.) to model long-running processes. External tasks can be integrated synchronously or asynchronously.
The runtime state of all process instances can easily be stored in a data source by turning on persistence (Chapter 5.1). Therefore, all processes can simply be restored in the state they were in after a server crash.
Drools Flow generates events about what is happening during the execution of your processes. By turning on audit logging (Chapter 5.3), these events can be stored in a database, providing a full audit history of whatever happened during execution.
The history data is stored using a few simple database tables. These tables can be queried directly, or you could use it for generating custom reports (Chapter 12.1) that show the key performance indicators that are relevant for your application.
Furthermore, we believe that a knowledge-oriented approach, allowing you to seamlessly combine processes with rules and event processing whenever necessary, will offer you more power and flexibility compared to aforementioned process-oriented engines.
Kris Verlaenen
Drools Flow Lead