Below are two pdf's which discuss and outline the Java Message Service, JMS, tutorial.

One Hour Java Messaging Service Tutorial
Advanced One Hour Java Messaging Service Tutorial

 

The original article was posted by Michael Veksler on Quora

A very well known fact is that code is written once, but it is read many times. This means that a good developer, in any language, writes understandable code. Writing understandable code is not always easy, and takes practice. The difficult part, is that you read what you have just written and it makes perfect sense to you, but a year later you curse the idiot who wrote that code, without realizing it was you.

The best way to learn how to write readable code, is to collaborate with others. Other people will spot badly written code, faster than the author. There are plenty of open source projects, which you can start working on and learn from more experienced programmers.

Readability is a tricky thing, and involves several aspects:

1. Never surprise the reader of your code, even if it will be you a year from now. For example, don’t call a function max() when sometimes it returns the minimum().
2. Be consistent, and use the same conventions throughout your code. Not only the same naming conventions, and the same indentation, but also the same semantics. If, for example, most of your functions return a negative value for failure and a positive for success, then avoid writing functions that return false on failure.
3. Write short functions, so that they fit your screen. I hate strict rules, since there are always exceptions, but from my experience you can almost always write functions short enough to fit your screen. Throughout my carrier I had only a few cases when writing short function was either impossible, or resulted in much worse code.
4. Use descriptive names, unless this is one of those standard names, such as i or it in a loop. Don’t make the name too long, on one hand, but don’t make it cryptic on the other.
5. Define function names by what they do, not by what they are used for or how they are implemented. If you name functions by what they do, then code will be much more readable, and much more reusable.
6. Avoid global state as much as you can. Global variables, and sometimes attributes in an object, are difficult to reason about. It is difficult to understand why such global state changes, when it does, and requires a lot of debugging.
7. As Donald Knuth wrote in one of his papers: “Early optimization is the root of all evil”. Meaning, write for readability first, optimize later.
8. The opposite of the previous rule: if you have an alternative which has similar readability, but lower complexity, use it. Also, if you have a polynomial alternative to your exponential algorithm (when N > 10), you should use that.

Use standard library whenever it makes your code shorter; don’t implement everything yourself. External libraries are more problematic, and are both good and bad. With external libraries, such as boost, you can save a lot of work. You should really learn boost, with the added benefit that the c++ standard gets more and more form boost. The negative with boost is that it changes over time, and code that works today may break tomorrow. Also, if you try to combine a third-party library, which uses a specific version of boost, it may break with your current version of boost. This does not happen often, but it may.

Don’t blindly use C++ standard library without understanding what it does - learn it. You look at std::vector::push_back() documentation at it tells you that its complexity is O(1), amortized. What does that mean? How does it work? What are benefits and what are the costs? Same with std::map, and with std::unordered_map. Knowing the difference between these two maps, you’d know when to use each one of them.

Never call new or delete directly, use std::make_unique and [cost c++]std::make_shared[/code] instead. Try to implement usique_ptr, shared_ptr, weak_ptr yourself, in order to understand what they actually do. People do dumb things with these types, since they don’t understand what these pointers are.

Every time you look at a new class or function, in boost or in std, ask yourself “why is it done this way and not another?”. It will help you understand trade-offs in software development, and will help you use the right tool for your job. Don’t be afraid to peek into the source of boost and the std, and try to understand how it works. It will not be easy, at first, but you will learn a lot.

Know what complexity is, and how to calculate it. Avoid exponential and cubic complexity, unless you know your N is very low, and will always stay low.

Learn data-structures and algorithms, and know them. Many people think that it is simply a wasted time, since all data-structures are implemented in standard libraries, but this is not as simple as that. By understanding data-structures, you’d find it easier to pick the right library. Also, believe it or now, after 25 years since I learned data-structures, I still use this knowledge. Half a year ago I had to implemented a hash table, since I needed fast serialization capability which the available libraries did not provide. Now I am writing some sort of interval-btree, since using std::map, for the same purpose, turned up to be very very slow, and the performance bottleneck of my code.

Notice that you can’t just find interval-btree on Wikipedia, or stack-overflow. The closest thing you can find is Interval tree, but it has some performance drawbacks. So how can you implement an interval-btree, unless you know what a btree is and what an interval-tree is? I strongly suggest, again, that you learn and remember data-structures.

These are the most important things, which will make you a better programmer. The other things will follow.

Static variables in Python are created as part of the class declaration.  By contrast, instance variables are created as part of a regular method and not a classmethod or staticmethod.

class A:
  i=3  # static variable
	
  def dosomethingregularmethod(self):
       self.k=4   # instance variable
	
# to access static variables


A.i

Getting involved with the IT, or Internet Technology industry, is a way for you to break into a variety of potential coveted career paths and job openings. Whether you prefer working with the back-end of programming or if you enjoy improve user experience while browsing online, there are many different in-demand IT skills that are useful to obtain today if you are seeking a career in the tech industry yourself.

Cloud Computing

Working with cloud computing, otherwise known as "the cloud", requires you to work within various types of servers that store and access data globally from any location. With the increase in mobile usage, cloud computing is becoming even more prevalent in today's society. When you want to work with cloud computing, understanding the basics of programming and network security is a must. Working in cloud computing is a way to help with building new applications, expanding companies online as well as allowing anyone internationally to locate and access a specific blog, website or mobile app.

UX Design

UX Design is also known as user experience design. A user experience designer specializes in understanding the usability and overall experience a web visitor has when browsing on a site or blog. UX design is essential to ensure that all visitors on a website are capable of navigating the blog properly and accessing the site's content with ease, regardless of the browser they are using or the type of device that is being used to access the site itself. Cross-browser compatibility and ensuring that all websites you are working with are accessible via mobile platforms is another responsibility of many UX designers today. Working in UX design is highly recommended if you believe you have an eye for "good" web design and if you have an interest in improving the overall experience web users for a specific audience have when visiting the blog or website you represent or that you are building for yourself.

IT Security

IT security is one of the fastest-growing positions throughout the entire IT industry and field. IT security requires you to understand network infrastructures as well as how to properly manage each server individually to provide security and protection from potential hackers and online thieves looking to steal sensitive data and information. Maintaining the security of a network and all servers for a company is only becoming more popular with the expansion of mobile phone usage along with the growth of the Internet altogether.

Understanding the variety of IT skills that are in demand today can help you to better decide on a path that is right for you. The more you understand about various IT skills, the easier it is to find a position or career in your future that is most suitable for the type of work you enjoy. Whether you are looking to develop new apps or if you are interested in managing the security of company servers, there are hundreds of positions and skills that are in demand in the IT industry today.

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