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 */

Social marketing firm Buddy Media is being bought out by Salesforce.com in a $689 million stock and cash deal. The transaction will close Oct. 31 (the end of the third fiscal quarter).

Among its 1,000 customer, Buddy Media includes the companies ofFord, Hewlett-Packard and Mattel. Thanks to its capabilities of sending targeted marketing content through YouTube, LinkedIn and Facebook, Salesforce.com will build on the monitoring technology in social media through its recent Radian6 purchase.

According to Salesforce.com CEO Marc Benioff, the Marketing Cloud leadership will enable the company to take advantage of the massive opportunity within the next five years.

The purchase is arriving on the heels of rival Oracle’s buyout of Virtue, who is the competitor to Buddy Media.

In programming, memory leaks are a common issue, and it occurs when a computer uses memory but does not give it back to the operating system. Experienced programmers have the ability to diagnose a leak based on the symptoms. Some believe every undesired increase in memory usage is a memory leak, but this is not an accurate representation of a leak. Certain leaks only run for a short time and are virtually undetectable.

Memory Leak Consequences

Applications that suffer severe memory leaks will eventually exceed the memory resulting in a severe slowdown or a termination of the application.

How to Protect Code from Memory Leaks?

Preventing memory leaks in the first place is more convenient than trying to locate the leak later. To do this, you can use defensive programming techniques such as smart pointers for C++.  A smart pointer is safer than a raw pointer because it provides augmented behavior that raw pointers do not have. This includes garbage collection and checking for nulls.

If you are going to use a raw pointer, avoid operations that are dangerous for specific contexts. This means pointer arithmetic and pointer copying. Smart pointers use a reference count for the object being referred to. Once the reference count reaches zero, the excess goes into garbage collection. The most commonly used smart pointer is shared_ptr from the TR1 extensions of the C++ standard library.

Static Analysis

The second approach to memory leaks is referred to as static analysis and attempts to detect errors in your source-code. CodeSonar is one of the effective tools for detection. It provides checkers for the Power of Ten coding rules, and it is especially competent at procedural analysis. However, some might find it lagging for bigger code bases.

How to Handle a Memory Leak

For some memory leaks, the only solution is to read through the code to find and correct the error. Another one of the common approaches to C++ is to use RAII, which an acronym for Resource Acquisition Is Initialization. This approach means associating scoped objects using the acquired resources, which automatically releases the resources when the objects are no longer within scope. RAII has the advantage of knowing when objects exist and when they do not. This gives it a distinct advantage over garbage collection. Regardless, RAII is not always recommended because some situations require ordinary pointers to manage raw memory and increase performance. Use it with caution.

The Most Serious Leaks

Urgency of a leak depends on the situation, and where the leak has occurred in the operating system. Additionally, it becomes more urgent if the leak occurs where the memory is limited such as in embedded systems and portable devices.

To protect code from memory leaks, people have to stay vigilant and avoid codes that could result in a leak. Memory leaks continue until someone turns the system off, which makes the memory available again, but the slow process of a leak can eventually prejudice a machine that normally runs correctly.

Related:

The Five Principles of Performance

In Demand IT Skills

One of the most recent updates to the iPhone, and more specifically the operating system that is packaged with the iPhone, iOS, brought one of the most fantastic and phenomenal updates ever: an update to Maps. Maps has been used as an application that provides an easy way to find routes, and (obviously) maps about certain areas, businesses in the local vicinity, and also leaving pins on favorited locations, or pins where you have explored, and for many other reasons. However, although Maps has always been a great way to travel with, it has always been redundant to travel with, also. When you used Maps a while ago, you had to route your map, and then manually click each next button as you reached each turn or freeway exit, and the like. So, if you had to turn left on a certain street, you had to tell your phone you had done so, so it would give you the next directions. As a result, it could become very dangerous to always have your phone out, looking at it, while you are on a high-speed freeway. But, the newest update solved that, and brought a great amount of new features.

Using Maps GPS

Using Maps is as easy as it gets. Most of the time, when you are using Maps, you are using it to search for a location, and finding a way to get there. To start off, let’s search for the nearest mall, and routes to get there. Simply search a nearby mall you know about, or search the general word “mall” by tapping on the top text box, and typing in mall, and searching. Pins will drop down on the screen, and locating the mall by zooming into certain streets and locations will help you find the mall you want. Once you find the mall you desire to go to, click on the blue arrow, and scroll down, and tap on the button that says “Directions To Here.”

As a result of tapping on that particular button, a new window should show up asking where your starting location is. On default, this location is your current location; if it is anything else, simply type in the starting location into the top address bar, such as your house. Once you are ready to go, tap on route, and you should be ready to go. Well, not exactly. One of the best features that has been implemented in the new system is suggested routes, and alternative routes. If you don’t like to drive on certain streets, or roads, the system provides you with different methods to get to your destination, which may avoid a road you don’t feel like driving on that certain day, or time, or you simply don’t want to take the freeway. It’s all okay, as Maps provides you with many different routes to take. Once you find the route you want (by tapping on the certain route’s outline), click start, and you should be ready to go. Make sure you turn up your volume so you can hear the directions!

Maps for Alternative Transportation