I will begin our blog on Java Tutorial with an incredibly important aspect of java development:  memory management.  The importance of this topic should not be minimized as an application's performance and footprint size are at stake.

From the outset, the Java Virtual Machine (JVM) manages memory via a mechanism known as Garbage Collection (GC).  The Garbage collector

• Manages the heap memory.   All obects are stored on the heap; therefore, all objects are managed.  The keyword, new, allocates the requisite memory to instantiate an object and places the newly allocated memory on the heap.  This object is marked as live until it is no longer being reference.
• Deallocates or reclaims those objects that are no longer being referened. 
• Traditionally, employs a Mark and Sweep algorithm.  In the mark phase, the collector identifies which objects are still alive.  The sweep phase identifies objects that are no longer alive.
• Deallocates the memory of objects that are not marked as live.
• Is automatically run by the JVM and not explicitely called by the Java developer.  Unlike languages such as C++, the Java developer has no explict control over memory management.
• Does not manage the stack.  Local primitive types and local object references are not managed by the GC.

So if the Java developer has no control over memory management, why even worry about the GC?  It turns out that memory management is an integral part of an application's performance, all things being equal.  The more memory that is required for the application to run, the greater the likelihood that computational efficiency suffers. To that end, the developer has to take into account the amount of memory being allocated when writing code.  This translates into the amount of heap memory being consumed.

Memory is split into two types:  stack and heap.  Stack memory is memory set aside for a thread of execution e.g. a function.  When a function is called, a block of memory is reserved for those variables local to the function, provided that they are either a type of Java primitive or an object reference.  Upon runtime completion of the function call, the reserved memory block is now available for the next thread of execution.  Heap memory, on the otherhand, is dynamically allocated.  That is, there is no set pattern for allocating or deallocating this memory.  Therefore, keeping track or managing this type of memory is a complicated process. In Java, such memory is allocated when instantiating an object:

String s = new String();  // new operator being employed
String m = "A String";    /* object instantiated by the JVM and then being set to a value.  The JVM
calls the new operator */

Every programming language has a mechanism to allow the programmer to create variables which hold custom data entered in by either the coder themselves or by the user of the application.

Regardless of whether you’re new to programming or not, you will have used variables and you should understand that in javascript they can hold any value such as a number or a string of text.

There is also another type of variable called an Array. Now, depending on who you talk to, some will say an array is actually an object, while others say it is a variable. Neither one is wrong but for the sake of simplicity we’ll refer to it as a variable.

Now, arrays are special because they can hold multiple values as opposed to standard variables which can only hold a single value at one time. If you can, try and imagine that your computer’s memory is made up of thousands of little boxes, and each of those boxes has an address which javascript will use to retrieve the array values when needed.

Controversy was recently courted as Southern California Edison (SCE) prepares to cut their own staff while looking to meet their staffing needs with offshore employees skilled in the field of “IT” or Informational Technology. This has been the second major utility company in the United States to take this path towards providing services to its consumers while holding current rates at consistent levels. SCE does not disclose the exact numbers of expected lay-offs, but the LA Times reports that it is in the hundreds.  Utility companies tell their consumers that these moves are necessary as a hedge against inflation and to keep their services at rates that their customers can easily afford. Critics claim that the use of foreign workers is the first step to using an entirely foreign workforce and promoting large scale unemployment amongst American citizens. Often this has been seen as a conflict between national and international workers for the same jobs, salaries and careers.

It has been noted that this State of California utility company, much like other corporations that hire foreign workers does so primarily when there is a shortage of national citizens that can perform these jobs well. IT workers that are brought in with H-1B Visa work permits usually are college educated and hold expertise in technical areas and studies that local employees may not be especially trained in. Once again, critics decry the fact that these employees are not hired directly. On shore contracting companies operating in the continental United States are directly hired by the utility companies. These contracted companies then serve as “middle-men” and hire a wide range of foreign workers with H-1B paperwork so that they can move to the United States. The workers then perform a variety of jobs instead of American workers who were either born in the country or have achieved American citizenship on their own.

Needless to say, the amount of visas issued in a given year is a concern for U.S workers in various fields but particularly in Information Technology. As large corporations stack the employment deck with foreign workers who put in the hours for a fraction of the pay-rate for local employees, local IT professionals are finding it more difficult to find work nationally.  They encounter rejections, endless interview processes or low –ball offers from companies and recruiting agencies looking to fill positions at a bare minimum cost for coveted skill-sets.  

Meanwhile, an H-1B worker is a worker brought in on a temporary basis with a visa allowing them to work freely in the United States. Much like a student or travel visa, it is issued for on a calendar oriented basis.  Applicants who successfully renew the visa for an extended period of time can expect to work in the United States for up to ten years.  Although U.S companies hiring these employees may pay them less than their local employees, the salaries earned by H-1B Visa workers are almost always higher than these workers would earn in their own country of origin.

Both sides can agree on several issues. When it comes to these H-1B Visa workers, their assignments are generally of a contractual nature and require them to reside in this country for a period of months to years. However it is also an accepted fact that while they are in this country, they are responsible for paying rent, utilities and all other living expenses. As residents of the United States on a permanent basis, they are also liable for taxes on any salary they have earned while living here.

Dr. Norman Matloff, a professor at the University of California, Davis and writer on political matters believes the shortage to be fiction. In his writing for the University of Michigan Journal of Law Reform, he claims that “there has been no shortage of qualified American citizens to fill American computer-related jobs, and that the data offered as evidence of American corporations needing H-1B visas to address labor shortages was erroneous. The American Immigration Lawyers Association (AILA) agrees with him and describes the situation as a crisis. Likewise, other studies from Duke, Alfred P. Sloan Foundation and Georgetown University have disputed that in some years, the number of foreign programmers and engineers imported outnumbered the number of jobs created by the industry

Learning SQL development can seem like an overwhelming task at first. However, mastering just a few key points will help ease your way through 80 percent of the day-to-day challenges when writing stored procedures and solving common problems. Here are three important SQL development factors to keep in mind:

Outer Joins
One of the most crucial things to understand in SQL server are joins. Joins are a way to retrieve data from two or more tables based on logical relationships between them. Joins dictate how Microsoft SQL Server ought to use data from one table to select the rows in another table.

In my experience inner joins are intuitive while outer joins can present additional hours of grief by overlooking associations in the other table(s). The outer join is the key to answering questions about what the database does not have. For example, if you need to make a query to display all the students who are without report-cards, you’ll need a left join to get all students coupled with a “where clause” to return the ones who have nulls for their report card table columns in the results.

Many talented Java script programmers have muddled through the SQL Server by deficient coding around the inner join. As a result, their queries can take five hours to run, whereas, properly written left joins, can take only two seconds to run.

Aggregation
Grouping results comes up in SQL a lot more than you might think. Knowing how to write a query when answering questions such as, “What’s the average grade for each teacher’s student list?” is invaluable. This kind of question cannot be answered with a single table or solely by joins.  You’ll often find you need to use joins in conjunction with group by statements. Always write the raw query first and then look at the results. Next, you have to figure out the best way to group them, rewrite your select clause and add a group by clause in the end.

Digging Through Data
I find this is the most lacking skill in many programmers. In fact, many otherwise-talented programmers holding Master’s Degrees fail to get jobs because they couldn’t analyze rows of data objectively during interviews. It’s just something that’s not taught but is crucial to get under you belt. Why? Eventually, some query is not going to perform as you may expect. And, the only way to find discrepancies is to look at rows of data, identify what join isn’t finding a match or where bad data is throwing things into chaos. Get familiar with how joins actually work, even if you have to manually walk through the logic of a large stored procedure’s tree of joins. It’s boring and time-consuming but absolutely necessary.

Take the time to master the core skills that will make you a successful SQL Programmer and avoid queries that run for five hours!