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 */

One of the most recent additions to the iPhone is the Photo Editor, directly in the iPhone. Added in the update that came from Apple over the summer, this new photo editor brings efficiency, and simplicity to photo editing, right in your phone. If you have a photo that you just took a moment ago of you with your friends, and you want to edit some features before posting it on a social networking site, it becomes simpler with this new addition, right in the Photos Application.

Open up the Photos application, and tap on a picture you would like to edit. Once your picture comes up, tap in the top right on the button named “Edit.” A user interface that deals with editing will show up, and you are ready to rock and roll. First off, many times we take pictures at weird angles, we take them sideways, upside down, to the right, to the left, and our phone doesn’t recognize them. In the bottom left, you will see an arrow that is pointing counter clockwise; this is the button that you want to press if you want to flip your picture around to the correct orientation. Keep in mind that this flips counter clockwise, and it doesn’t matter if you pass the orientation that you wanted. Just keep flipping!

Next up is the simple enhance tool. Sometimes colors get drowned out if we don’t have the right lighting in our pictures, and makes the photo look dull, and dreary. You don’t want your colors to look dull and dreary while you are celebrating your trip to New York and seeing Times Square! Tapping on the button that looks similar to a magic wand, your picture will begin to look brighter and fuller. With the tap of a button, the iPhone detects what points in the picture is, as we said earlier, “dull, and dreary” and enhances those colors to their predicted colors, if the light was in the correct intensity. However, if you are dissatisfied with the outcome of the enhance tool, if your picture is not handled well by the phone, you are able to tap on the wand again, and remove your auto enhance.

In the rare case of red eye in your picture, the new photo editor has a solution. Moreover, a one-tap solution. With a simple tap on the red eye correction tool, between the crop tool, and the auto-enhance tool, you bring up a screen where you are now able to tap anywhere on your photo where red eye exists, and remove it. As simple as that. Remember when you had to do crazy dragging, selection, and odd stunts to remove red eye? Not any more.

As part of our Java Tutorials program, we will list a number of interview questions to aid in a better understaing of Java and J2EE and, hopefully, provide a greater likelihood of getting a job.  Let us begin with the basics:

1. What is meant by J2EE?

J2EE is an abreviation for Java 2 Platform Enterprise Edition

2.  What is the purpose of J2EE?

The purpose of J2EE is to provide a component based platform in a multitier application model with transaction management, web services and reusable component support.

3.  What is the tier structure of the typical J2EE application?

A typical J2EE application consists of the following tiers/machines:  the client machine (browser/non-browser application), the J2EE server (an application server such as Oracle, JBoss, GlassFish, Tomcat) and a database.