Design Patterns in OOPs

Introduction:


For starting with Design Patterns, pre-requiste is one should aware with the Object oriented concepts.

Here, we will try to simplify the term and purpose of the Design Pattern.

First normal and very common query could be, What is Design Patterns, why they are used?

In a simple layman term, a design pattern is a general reusable solution to a commonly occurring problem in software design.

Defining Design Patterns more descriptively...

In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code.

It is a simply a description for how to solve a problem that can be used in many different situations.

Design patterns is used to speed up the development process by providing tested, proven development methods or paradigms. Effective software design requires considering issues that may not become visible until later in the implementation.

Reusing design patterns helps to prevent subtle issues that can cause major problems, and it also improves code readability for coders and architects who are familiar with the patterns.
Digging into depth,
Design Pattern is categoried in three different sub patterns.

Creational Patterns
Structural Patterns
Behavioral Patterns.

Creation Patterns
This design pattern is all about class instantiation.

This pattern can be further divided into class-creation patterns and object-creational patterns.

Abstract Factory : Creates an instance of several families of classes
Factory : Creates an instance of several derived classes
Builder : Separates object construction from its representation
Prototype : A fully initialized instance to be copied or cloned
Singleton : A class of which only a single instance can exist

Structural patterns
This design patterns is all about Class and Object composition. Structural class-creation patterns use inheritance to compose interfaces. Structural object-patterns define ways to compose objects to obtain new functionality.

Adaptor : Match interfaces of different classes
Bridge : Separates an object’s interface from its implementation
Decorator : Add responsibilities to objects dynamically
Facade : A single class that represents an entire subsystem
Proxy : An object representing another object

Behavioral patterns
This design patterns is all about Class's objects communication. Behavioral patterns are those patterns that are most specifically concerned with communication between objects.

Chain of responsibilty : A way of passing a request between a chain of objects
Command : Encapsulate a command request as an object
Interpreter : A way to include language elements in a program
Iterator : Sequentially access the elements of a collection
Observer : A way of notifying change to a number of classes
State : Alter an object's behavior when its state changes
Visitor : Defines a new operation to a class without change

Now we will pick the popular and commonly used design pattern and explain in detail.
Staring with the Factory Pattern.

What is a "factory" and why would you want to use one?
A factory, in this context, is a piece of software that implements one of the "factory" design patterns introduced . In general, a factory implementation is useful when you need one object to control the creation of and/or access to other objects. By using a factory in RMI, you can reduce the number of objects that you need to register with the RMI registry.

Examples of Factories in the Real World:
The Bank
The Library
These two example is sufficient to understand the actual process of the Factory Patterns. These examples are from the real life.

Let's take the example, commonly illustrated in the text book, GoF.
Widgets in a GUI Environment.
This example explains , how an Abstract Factory can be used to create widgets for a GUI environment. By designing the client to use the Abstract Factory interface, different factories can be created to generate different sets of widgets without requiring changes to the clients. This example is not intended to illustrate a useful implementation of Abstract Factory, as Java's AWT and Swing do the work for you, but it does show how easily design patterns can be implemented in RMI.
One other point to notice is how the pattern is split between client and server. This split was arbitrarily chosen, and with RMIs object-oriented nature you could decide to make the split in the pattern elsewhere.

In General , this pattern consists of two class hierarchies, one of Products, and one of Creators. Each ConcreteCreator class creates instances of specific ConcreteProduct classes using a factory method.

The factory pattern can help solve your application issues. For example, developers often must reply to users based on each user’s machine, creating multiple hardware issues. The factory pattern can streamline the process. The concept is simple, but the solutions created with the factory pattern are powerful.

For more understanding, let's take one more example.
Communications breakdown
Consider the example of a data collection application where various field devices supply data to the application via TCP/IP sockets. The application was originally written to communicate with one device but was expanded when the company produced a newer version. Unfortunately, this new hardware did not speak the same language as the previous version. Marketing required the application to support both hardware versions, since customers might buy new units and install them in tandem with older units. The factory pattern eased the burden of supporting multiple device types.

In short and effective explanation of fatory pattern is :
=> if we have a super class and n sub-classes, and based on data provided, we have to return the object of one of the sub-classes, we use a factory pattern.

Now, we will focus on the positive and negative points on using the Factory Patterns.
Positives:
-Eliminates the need to bind application-specific classes into your code
-Provides hooks for subclassing. Creating objects inside a class with a factory method is always more flexible than creating an object directly. This method gives subclasses a hook for providing an extended version of an object.
-Connects parallel heirarchies. Factory method localises knowledge of which classes belong together. Parallel class heirarchies result when a class delegates some of its responsibilities to a separate class.
Negatives:
-Clients might have to subclass the Creator class just to create a particular Concreate object.

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Fear About US Recession.. Impact on Jobs

US market recession is almost declared, till now it was just a fear about the condition, by the time Mr. Warren Buffett admitted in his recent Interview and accepted about the chances of recession in US, and it could go even worst till ever happened.

Since US market is predominately considerable and play a major role all over the world' s economy, in all trades and businesses. So it's quite obvious to get scared from this situation.
Being an IT professional it's an obvious concern and worry to look into and know what is the scenario. To know, the fact and figures why are the people really scared about.

Curiously and sacredly I tried to compile the scenarios, which is I am sharing with . Most of the data I have taken the reference with nytimes.

The job market took a serious and unexpected turn for the worse in August, raising fears that the risks of a recession are greater than many economists had believed.

According to "The New York Times" , the economy shed 4,000 jobs between July and August, with industries that are connected to the housing market — like construction and manufacturing — making the deepest cuts, the Labor Department reported today. It was the first employment decline since 2003, when the job market was still struggling to emerge from a long slump in the wake of the 2001 recession.

The unemployment rate held steady at 4.6 percent in August, which economists said was likely a statistical fluke as more people stopped looking for work and were therefore not counted by the government as unemployed.

“If the economy is not headed toward recession, it is very close to one,” said Mark Zandi, chief economist in one of the .com site interview.

Stocks fell broadly and sharply, as investors digested the idea that the economy had been weakening significantly even before the mortgage crisis hit financial markets last month. The Dow Jones industrial average closed down almost 250 points, or 1.9 percent.
The jobs report all but guarantees that the Federal Reserve will cut its benchmark short-term interest rate when its policy-making committee meets on Sept. 18. A quarter-point reduction to 5 percent remains the most probable move, although a half-point cut now cannot be ruled out, economists said.

The weakness of the employment data seemed to change the terms of the debate over the health of the economy. The chances of a recession over the next year now seem to be somewhere between one-quarter and one-half, economists interviewed today said.
“I think at least people need to start thinking about the housing market not just as some ring fence problem which is off on its own, and the rest of the economy is doing just fine,” said Nigel Gault, chief United Economist with Global Insight, an economic research firm in Lexington, Mass. “They need to start worrying about the health of the broader economy.”

The Bush administration tried to defuse concerns that the weak jobs numbers hinted at a wider economic slowdown.

In an interview , the Treasury secretary, said the report was “not totally surprising.”
“There will be news that isn’t always good news,” he said. “But I feel quite strongly that we have a resilient economy.”


For months, Fed officials and Wall Street forecasters have been predicting that the housing slump would slow the economy, but that other strengths — like corporate earnings, growth in other countries and strong wage growth — would keep the slowdown from being severe. That could still happen; in both the 1980s and 1990s economic expansions, employment fell at least once before quickly reversing course.

“The financial turmoil and extended problems in housing put the risks for the economy clearly to the downside — no question,” said Mickey Levy, chief economist for Bank of America. “But there are also factors that suggest a longer period of slower growth, but not recession.”

One of the most worrisome signs in the jobs report was the government’s revision to its employment data for June and July. The new numbers show just under 70,000 jobs created in each of the two months, down from an average of almost 110,000 according to its initial estimates.

In 2005 and 2006, the average monthly job growth was slightly above 200,000.
The sharp slowdown this year suggests that some employers have already begun to see a downturn in their business and others believe that one is on the way. With falling house prices in most of the country and rising oil prices, consumer spending has slowed modestly in recent months.

State and local government agencies, many of them dealing with budget shortfalls connected to the housing slump, have also cut an average of 27,000 jobs a month over the last three months. But economists said the declines in government employment, especially in schools, may have reflected seasonal quirks that made the job market look worse last month than it truly was.
Hospitals, doctors’ offices, restaurants and retailers all added jobs in August.

But the bright spots were few and far between. Employment in the finance sector — which includes real estate agencies and accounts for about 8.5 million of the country’s 138 million jobs — was flat in August, which could be a sign that the government numbers have not yet captured some of the mortgage-related job cuts now occurring.

The surveys that made up the Labor Department report measured employment from Aug. 12 to Aug. 18, when the credit squeeze and subsequent stock market turmoil were under way but not fully felt. Since then, some large lenders like Countrywide and Lehman Brothers have continued to lay off workers. And just today, IndyMac Bancorp, a large mortgage lender, said it would be cutting about 1,000 jobs over the next several months.

“There probably was not that much influence in the data from the credit shock,” said Richard Berner, chief United States economist at Morgan Stanley. “So I think more weakness in the economy is likely. The economy is clearly losing momentum.”

The extent to which the economy continues to lose momentum will determine the Fed’s course of action. The price of a futures contract tied to Fed policy shows that the central bank will probably cut the benchmark rate, now at 5.25 percent, to 4.5 percent by the end of the year. But a growing number of economists are saying that might not be soon enough.

Mr. Gault of Global Insight, who is forecasting a half-point cut on Sept. 18, said it would send “an important message that the Fed sees there are real problems here, there’s a real threat, and it needs to have a response that’s commensurate to that threat.”

Although the unemployment rate held steady at 4.6 percent, the percentage of adults with jobs fell to 62.8 percent, from 63 percent in July and a peak of 63.4 percent in December. The number of people who were neither working nor looking for work — and thus considered neither employed nor unemployed by the government — rose by almost 600,000 in August.

“That’s a sign of economic weakness,” Mr. Anderson, of Wells Fargo, said. “Perhaps people just gave up trying to find jobs.”
The number of people with part-time jobs who said they would prefer to full time has also been rising in recent months. In August, the Labor Department classified 4.5 million workers as “part time for economic reasons,” up from 4.3 million in July.

Wage growth, which often lags behind job growth, did continue at roughly its recent pace. Average hourly earnings for rank-and-file workers — who make up about four-fifths of the work force — have increased 3.9 percent over the last year, to $17.50. Inflation has been running at about 2.5 percent a year.

Wall Street had eagerly awaited the jobs report because it was the most significant economic data released since financial markets began to tumble in early August. If the jobs report had been merely lackluster, it might have been welcomed by investors as a sign that a Fed rate cut all but certain and the economy was still growing at a healthy pace.

The reversal in job growth, however, was far different from the gain of roughly 100,000 jobs that Wall Street was expecting, raising worries that corporate profits will weaken as the market upheaval moves beyond the housing and financial sectors.

<<All these data, statistics and above figure stats, I have complied through internet sites and other sources.>>

DON'T CHALLENGE MECHANICAL FOR IT...

General Motors REPLY TO BILL GATES...

At a recent computer expo (COMDEX), Bill Gates reportedly compared the computer industry with the auto industry and stated, "If GM had kept up with technology like the computer industry has, we would all be driving $25.00 cars that got 1,000 miles to the gallon."

In response to Bill's comments, General Motors issued a press release Stating:

"If GM had developed technology like microsoft, we would all be driving cars with the following characteristics (and I just love this part, esp 7th point and 10'th point):

1. For no reason whatsoever, your car would crash twice a day.

2. Every time they repainted the lines in the road, you would have to buy a new car.

3. Occasionally your car would die on the freeway for no reason. You would have to pull to the side of the road, close all of the windows, shut off the car, restart it, and reopen the windows before you could continue. For some reason you would simply accept this.

4. Occasionally, executing a maneuver such as a left turn would cause your car to shut down and refuse to restart, in which case you would have to reinstall the engine.

5. Macintosh would make a car that was powered by the sun, was reliable, five times as fast and twice as easy to drive - but would ! run on only five percent of the roads.

6. The oil, water temperature, and alternator warning lights would all be replaced by a single "This Car Has Performed an Illegal Operation" warning light.

7. The airbag system would ask "Are you sure?" before deploying.

8. Occasionally, for no reason whatsoever, your car would lock you out and refuse to let you in until you simultaneously lifted the door handle, turned the key and grabbed hold of the radio antenna. (Read CTR-ALT-DEL)

9. Every time a new car was introduced car buyers would have to learn how to drive all over again because none of the controls would operate in the same manner as the old car.

10. You'd have to press the "Start" button to turn the engine off. "

Are you Serial Killer!!!

Test your self...

A woman, while at the funeral of her own mother, met a guy whom she did not know. She thought this guy was amazing.

She believed him to be her dream guy so much, that she fell in love with him right there, but never asked for his number and could not find him.
A few days later she killed her sister.

Question: What is her motive for killing her sister?

Management Lesson...

Big John doesn't pay!

One fine day, a bus driver went to the bus garage, started his bus, and drove off along the route. No problems for the first few stops - a few people got on, a few got off, and things went generally well. At the next stop, however, a big hulk of a guy got on. Six feet eight, built like a wrestler, arms hanging down to the ground. He glared at the driver and said, "Big John doesn't pay!" and sat down at the back.

Did I mention that the driver was five feet three, thin, and basically meek? Well, he was. Naturally, he didn't argue with Big John, but he wasn't happy about it. The next day the same thing happened - Big John got on again, made a show of refusing to pay, and sat down. And the next day, and the next! .

This grated on the bus driver, who started losing sleep over the way Big John was taking advantage of him. Finally he could stand it no longer. He signed up for body building courses, karate, judo, and all that good stuff.

By the end of the summer, he had become quite strong; what's more, he felt really good about himself. So on the next Monday, when Big John once again got on the bus and said, "Big John doesn't pay!"

The driver stood up, glared back at the passenger, and screamed, "And why not?" With a surprised look on his face, Big John replied, "Big John has a bus pass."

Management Lesson :
"Be sure there is a problem in the first pla ce before working hard to solve one."

What is ESP, Do you believe in?

"ESP, extra-sensory perception, is most commonly called the "sixth sense." ESP is an ability beyond the normal.
It means you have experiences with spirits, future events, and psychic dreams. ESP is an ability that most cant control, but a lot of people are gaining knowledge, and warnings from it. So ESP is what it says: Extra Sensory Precept ion.

I personally believes in; there is some super natural happening that is beyond our control. There is something which is controlling ourselves. I strongly believe in palmistry , astrology, numerology and the behaviour psychology of humans studies . There could be any future predictions can be done on the combination of all these and that too very accurate.

There would be many who disagree with me, in this context.

I believe every one is having some sixth sense or ESP , which could clearly indicate about the good or bad happenings , in the form of different omens . Everyone is having the ability, whether or not its just sensing things, or dreaming things. Whether the people believe it or not, this is having all of us.
It's just a matter of sensing and concentrating over.

There are many evidences which is helpful in demonstrating that ESP does exist. I was going through some forum or some book, that ESP cannot be explained or quantified by physical laws; and furthermore, that the mind (consciousness) and the brain are two separate entities. Simultaneously, research in quantum physics points to the existence of a second, non material universe. So, the time is fast approaching when Western scientists must come to terms with the Eastern mystical concept: "that an extrasensory force exists in another realty, and intersects and integrates with the physical world."

There are much more studies or the believing which could be framed in this categories , like
if someone can tell a lot about you without knowing you. This is known as cold reading, and it's based upon observing the way you look and act. Like it can easily be guessed , the way you dress tells a lot about your social standing, and there are lots of other little things to look for. This I guess we can develop the ability using Human Psychology.

One more thing I am interested in is Aura. Aura is an energy around you. Studies evolves around energy colors like : Blue, green, red, black, white, orange, yellow, sky blue.

But I don't know much details about this , and definitely would like to know much about Aura. That how these energy color impact on us positively or negatively . How we can make the maximum benefits of these color energies.

Thailand

Another beautiful destination of southeast destination... Thailand. Captital is Bangtok

It is having rich natural beauty, inspiring temples, and famous for the it;s hospitality.