Use of Private Constructor in OOPS

If we set access specifier of a constructor to private, then that constructor can only be accessed inside the class. A private constructor is mainly used when you want to prevent the class instance from being created outside the class. 

This is mainly in the case of singleton class. Singleton classes are employed extensively in concepts like Networking and Database Connectivity. Using private constructor we can ensure that no more than one object can be created at a time. 

Example of Private Constructor in a Singleton Class

public class SingletonClass

{

    public static SingletonClass singletonClass;

    private SingletonClass() 

    {

    }

    public static SingletonClass getInstance() 

    {

        if(singletonClass == null) 

        {

            singletonClass = new SingletonClass();

        }

        return singletonClass;

    }

}

A class with private constructor cannot be inherited.

If we don’t want a class to be inherited, then we make the class constructor private. So, if we try to derive another class from this class then compiler will flash an error. Why compiler will flash an error? 

We know the order of execution of constructor in inheritance that when we create an object of a derived class then first constructor of the base call will be called and then constructor of derived class. Since base class constructor is private, hence, derived class will fail to access base class constructor.

We can also use sealed class to stop a class to be inherited. Sealed class provide more flexible and readable way to stop inheritance.

Diamond Problem in Multiple Inheritance in OOPS

The diamond problem occurs when two super classes of a class have a common base class. 

Suppose there are four classes A, B, C and D. Class B and C inherit class A. Now class B and C contains one copy of all the functions and data members of class A. Class D is derived from class B and C. Now class D contains two copies of all the functions and data members of class A. One copy comes from class B and another copy comes from class C.

Let’s say class A has a function with name display(). So class D have two display() functions as I have explained above. If we call display() function using class D object then ambiguity occurs because compiler gets confused that whether it should call display() that came from class B or from class C. If you will compile above program then it will show error.

This kind of problem is called diamond problem as a diamond structure is formed (see the image).

That is why major programming languages like C#, Java and Delphi don't have multiple inheritance because it can lead to diamond problem and rather than providing some complex way to solve it, there are better ways through which we can achieve the same result as multiple inheritance. We can use interfaces to resolve this problem.

C++ supports multiple inheritance.

Notice that the above problem with multiple class inheritance can also come with only three classes where all of them has at least one common method.

Because of this problem we can not extend two classes for implementing multiple inheritance and to resolve this problem of multiple inheritance in object oriented programming we use interfaces for implementing the functionality of multiple inheritance. 

As we know we do not define a function but only declare that function in an interface. So if we use interfaces we can extend one class and one or more interfaces or we can implement more than one interfaces at a time to use the functionality of multiple inheritance and we can escape from diamond problem.

How to declare Static/Class variables, properties, functions and procedures in Delphi?

In Delphi, we do have static variables, properties, functions and procedures, but instead of the word "static" we refer the word "class". In this tutorial, I have shown the syntax of declaring the static variables, properties, functions and procedures in Delphi. We don't have to use "static" keyword while declaring the static variables and properties, just use "class" keyword. While declaring static functions and procedures, we have to use both "class" and "static" keyword.

Declare a static/class variable in Delphi

type

  TStaticDemoClass = class(TObject)

  public

    class var StaticVar: integer;

  end;

Declare a static/class property in Delphi

type

  TStaticDemoClass = class(TObject)

  private

    class var FStaticVar: integer;

  public

    class property StaticVar: integer read FStaticVar write FStaticVar;

  end;

Now we can use above StaticVar variable/property anywhere in the unit like this:

procedure TForm1.Button1Click(Sender: TObject);

var a:integer;

begin

  TStaticDemoClass.StaticVar := 1;

end;

We can also use static/class functions and procedures in Delphi. Below example, I have copied from documentation:

type

  TMyClass = class

    strict private

      class var FX: Integer;

    strict protected  

      //Note: accessors for class properties must be declared class static.

      class function GetX: Integer; static;

      class procedure SetX(val: Integer); static;

    public

      class property X: Integer read GetX write SetX;

      class procedure StatProc(s: String); static;

  end;

TMyClass.X := 17;

TMyClass.StatProc('Hello');

You need to use "static" keyword after function / procedure declaration. Classes can have static class methods -- i.e. methods that can be called from a class type. Class static methods can be accessed without an object reference. Unlike ordinary class methods, class static methods have no Self parameter at all. They also cannot access any instance members. They still have access to class fields, class properties, and class methods. Also unlike class methods, class static methods cannot be declared virtual.

VCL Hierarchy in Delphi: Types of Controls in Delphi: TWinControls and TGraphicControls

In VCL (Visual Component Library) hierarchy, you will find TObject at the top, then TPersistent, then TComponent and then TControl.

TObject >> TPersistent >> TComponent >>TControl

VCL Hierarchy in Delphi

TObject is the base class from which all classes descend.

TPersistent class descends directly from TObject. The special characteristic of TPersistent is that it is an abstract class that defines the methods that allow it to be streamed.

TComponent is the base class from which all components descend. Non-visual components are descendants of TComponent. For example: TTimer

TControl is the base class from which all the visual components descend. For example: TEdit, TListBox, TComboBox etc.

Again, there are two types of controls (TControl): Window Controls (TWinControl) and Graphic Controls (TGraphicControl)

Following is the difference between TWinControl and TGraphicControl in Delphi:

TWinControls

TWinControls can receive input focus and they can be parents to other controls.

Example: TEdit, TListBox and TComboBox

TGraphicControl

TGraphicControls differ from TWinControls in that they cannot receive input focus. Also, they cannot be parents to other controls.

Example: TLabel

TGraphicControls are used when you want to display something on the form.

Two key advantages of TGraphicControls over TWinControls:

1. TGraphicControls don't use up system resources since they don't require a window handle.

2. They are a bit faster at drawing than their TWinControl counterparts since their painting is not subject to the windows message dispatching system. Instead, they piggyback on their parent's paint process.

For more details, please refer to documentation.

What is the difference between Singleton Class and Static Class? Which one to use and when?

Almost both singleton class and static class serve the same purpose which creates confusion among developers and architects about which one to use. When to use singleton class and when to use static class. In this article I have tried to differentiate between the two. Following is the list of differences between a singleton class and a static class:

1. Singleton classes are more inclined to the object-oriented concepts as compared to the static classes. With Singleton classes, you can use inheritance and polymorphism to extend a base class, implement an interface and capable of providing different implementations. While a static class cannot inherit their instance members. So, Singleton classes are more flexible than static classes.

2. Singleton classes can be passed as an object to other methods while a static class allows only static methods and you cannot pass static class as parameter.

3. If your requirement is to maintain the state, then singleton class is the better choice than static class, because maintaining the state with static classes is very cumbersome and leads to subtle bugs.

4. Singleton classes can be lazy loaded if it’s a heavy object, but static class doesn't have such advantages and always eagerly loaded. Static class is generally initialized when it is first loaded and it will lead to potential class loader issues.

5. Static classes are hard to mock and consequently hard to test than singletons, which are easy to mock and thus easy to test. It’s easier to write unit tests for singleton than static classes, because you can pass mock object whenever singleton is expected, e.g. into constructor or as method arguments.

6. Singleton classes provide more flexibility. Consider the possibility that your application has a global shared object and tomorrow you decide that you must make more than one instance of the class. If you use a singleton class then all you should do is make the constructor public. This is not so simple with static classes.

7. Many Dependency Injection framework manages singleton quite well e.g. Spring, which makes using them very easy.

8. Singleton objects are stored in Heap, but static objects are stored in Stack.

9. Static class provides better performance than singleton class, because static methods are bonded on compile time.

10. Singleton classes maintain single object across the application life cycle, so the scope is at application level. The static does not have any object pointer, so the scope is at App Domain level. Moreover, both should be implemented to be thread-safe.

Security and Privacy issues with IoT (Internet of Things) - Top barriers to IoT success

IoT is one of the biggest breakthroughs in the history of the tech industry. It will soon be an inherent part of every aspect of our lives. Security and Privacy are the most significant challenge for the IoT. Security and Privacy issues are acting as top barriers to IoT success. So, addressing underlying security and privacy concerns is very crucial. 

As more and mored devices are being added to the IoT everyday, privacy and security concerns are becoming vital. 

Security issue with IoT devices

Security is one of the main concerns of the IoT ("Internet of Things"). With billions of devices connected to the internet, it is needless to say that to protect your connected devices from malware penetrations is a real challenge. Security risks of IoT devices cannot be ignored whether it is from hackers or corporations. Increasing the number of connected devices increases the opportunity to exploit security vulnerabilities.

When IoT devices are connected to the cloud or data centers via internet, they get under the risk of being accessible to the outside world. Poorly designed devices can easily expose user data to theft. 

There are many reasons behind the state of insecurity in IoT. 

Companies do not update their devices enough or at all. This means that an IoT device which was safe when you first bought it can become unsafe as hackers discover new vulnerabilities.

The fundamental security weakness of the Internet of Things is that it increases the number of devices on the internet. Earlier, most of us had to only worry about protecting our computers, then, we had to worry about protecting our smartphones as well, and now after IoT, we have to worry about protecting our car, our home appliances, our wearables, and many other IoT devices.

Because there are so many devices that can be hacked, that means that hackers can accomplish more. You may have heard about how hackers could potentially remotely control cars and remotely accelerate or decelerate the car. But hackers could use even seemingly unimportant devices like baby monitors or your thermostat to uncover private information or just ruin your day. The point is that we have to think about what a hacker could do with a device if he can break through its security. 

In this way, our normal day to day life and health can become the target of IoT hack attacks. Urban infrastructure can also become a target for hackers.

Privacy issue with IoT devices

Corporations which create and distribute interconnected devices could also use these devices to obtain personal data, particularly dangerous when used for money transfers. Manufacturers can steal the information about your habits and misuse it. 

For example, consider how some companies are distributing Fitbits to their employees so that they can track their health and thus get lower health insurance premiums. Even if we ignore the worrying idea of workers’ health being monitored by corporations around the clock, there is the question of what corporations can do with the data they have gathered. Companies can attempt to send or even sell gathered data to other companies, which raises issues regarding our individual privacy rights.

Vision features and voice recognition are now being integrated into smart TVs. These features can listen continuously to conversations or look for activity and transmit data selectively to cloud services for processing. These cloud services may sometimes even include third parties. The collection of all this information faces a number of regulatory and legal challenges.

The collection of private information exposes legal and regulatory challenges facing data protection and privacy law. There are a wide range of regulatory and legal questions surrounding the IoT, which need thoughtful consideration. Legal issues with IoT devices include crossborder data flow, conflict between law enforcement surveillance and civil rights, data retention and destruction policies, and legal liability for unintended uses, security breaches or privacy lapses. 

In short, Security and Privacy issues are the biggest issues which consumers, businesses and governments need to consider before using IoT connected devices.

Real World Examples of IoT (Internet of Things) - How will IoT change our lives?

IoT (Internet of Things) is going to change our lives to a large extent. In the coming years, we will realize the real potential of IoT. Below are some real world examples of IoT.

Lets consider IoT enabled Alarm Clock or say Smart Alarm.

Imagine you wake up at 7am every day to go to work. Your alarm clock does the job of waking you just fine. That is, until something goes wrong. Your train is cancelled and you have to drive to work instead. The only problem is that it takes longer to drive, and you would have needed to get up at 6.45am to avoid being late. Oh, and it’s pouring with rain, so you’ll need to drive slower than usual. 

A connected or IoT-enabled alarm clock would reset itself based on all these factors, to ensure you got to work on time. It could recognize that your usual train is cancelled, calculate the driving distance and travel time for your alternative route to work, check the weather and factor in slower travelling speed because of heavy rain, and calculate when it needs to wake you up so you’re not late. 

If it’s super-smart, if might even sync with your IoT-enabled coffee maker, to ensure your morning caffeine’s ready to go when you get up.

Now consider IoT enabled car or say connected cars.

Having been woken by your smart alarm, you’re now driving to work. On comes the engine light. You’d rather not head straight to the garage, but what if it’s something urgent? In a connected car, the sensor that triggered the check engine light would communicate with others in the car. A component called the diagnostic bus collects data from these sensors and passes it to a gateway in the car, which sends the most relevant information to the manufacturer’s platform. The manufacturer can use data from the car to offer you an appointment to get the part fixed, send you directions to the nearest dealer, and make sure the correct replacement part is ordered so it’s ready for you when you show up.

You are on your way to a meeting; your car could have access to your calendar and already know the best route to take. If the traffic is heavy your car might send a text to the other party notifying them that you will be late. 

Now consider IoT enabled homes or say smart homes.

Take an instance where you need to monitor your home or child when you are away. A simple solution would be to fix an IP camera and monitor its feed using a web or mobile application. You can even hire a babysitter. The former option can give you the complete monitoring data, while the latter cannot. If you fix sensors or devices, which can be reached from anywhere, you have the flexibility to monitor as well as control those devices to the best of their ability; this can make your home or baby 99.99% secure. 

Your home security system, which already enables you to remotely control your locks and thermostats, can cool down your home and open your windows, based on your preferences.

British Gas's Hive Active Heating enables consumers to control their home heating from their smartphone, laptop or tablet. It even has the ability to turn off when no one is home by detecting whether your smartphone is in the house or not.

IoT can help in reducing accidents and save valuable human life.

Let’s look at one example. In 2007, a bridge collapsed in Minnesota, killing many people, because of steel plates that were inadequate to handle the bridge’s load. 

When we rebuild bridges, we can use smart cement: cement equipped with sensors to monitor stresses, cracks, and war-pages. This is cement that alerts us to fix problems before they cause a catastrophe. And these technologies aren’t limited to the bridge’s structure.

If there’s ice on the bridge, the same sensors in the concrete will detect it and communicate the information via the wireless internet to your car. Once your car knows there’s a hazard ahead, it will instruct the driver to slow down, and if the driver doesn’t, then the car will slow down for him.

And thus bridges become smart bridges, and cars smart cars. And soon, we have smart cities, and….

Airplane manufacturers are building air-frames with networked sensors that send continuous data on product wear and tear to their computers, allowing for proactive maintenance and reducing unplanned downtime. 

Now consider some more examples of Real World IoT:

Some insurance companies, for example, are offering to install location sensors in customers’ cars. That allows these companies to base the price of policies on how a car is driven as well as where it travels. Pricing can be customized to the actual risks of operating a vehicle rather than based on proxies such as a driver’s age, gender, or place of residence.

Sensors in even the domestic animals. In the world of IoT, even the domestic animals will be connected and monitored with the help of embedded sensors. This allows farmers to monitor their animal's health and track their movements, ensuring a healthier, more plentiful supply of milk and meat for people to consume. 

Some more...

What if your office equipment knew when it was running low on supplies and automatically re-ordered more? 

What if your refrigerators can warn you when you’re out of milk. 

What if smart dustbins can signal when they need to be emptied.

What if smart tea maker that knows just when you’re in need of a cup of tea.

Truly speaking, you can think of infinite examples of IoT in the real world. It cannot be summarized in an article. There is no limit. Just keep thinking...

Other articles on IoT:

Internet of Things (IoT) - Next Stage of Information Revolution

Internet of Things (IoT) - Next Stage of Information Revolution

The term "Internet of Things" was first coined by Kevin Ashton, cofounder and executive director of the Auto-ID Center at MIT in 1999.

The "Internet of Things (IoT)" is the next stage of the Information Revolution. 

What is IoT (Internet of Things)?

IoT refers to the connection of devices (other than computers, smartphones and tablets) to the Internet via embedded sensors. It allows devices to talk to us and talk to each other. So, IoT can also be defined as a network of internet-connected devices able to collect and exchange data using embedded sensors. 

A thing, in the "Internet of Things", can be a person with a heart monitor implant, a farm animal with a bio-chip transponder, an automobile that has built-in sensors to alert the driver when tire pressure is low or any other natural or man-made object (almost anything else you can think of) that can be assigned an IP address and provided with the ability to transfer data over a network with the help of embedded sensors. 

Earlier the data was created by people on the internet, but now the data will be created by the things (living or non-living) without any human intervention.

IoT Devices

Any stand-alone internet-connected device that can be monitored and/or controlled from anywhere. It should have embedded sensors and on/off switch. It should have the ability to represent itself digitally means it can be assigned an IP address and have the ability to collect and transfer data over a network without manual assistance or intervention. 

Due to the limited address space of IPv4 (which allows for 4.3 billion unique addresses), IoT devices will have to use the next generation of the Internet protocol (IPv6) to scale to the extremely large address space required.

Examples of IoT Devices: Smartwatch, TV,  Refrigerators, Washing Machines, Kitchen Appliances, Thermostats, Cars, Switches, Lights, Blood Pressure and Heart Rate Monitors, Smart grids, Virtual Power Plants, Intelligent Transportation and anything you can think of.

Basically, if your fridge or TV has an Internet connection, then it becomes an IoT device.

If your coffee maker connects to an app on your smartphone that allows you to begin brewing with a tap on your screen, that coffee maker becomes part of the Internet of Things.

As per IoT, Anything that can be connected, will be connected. Connect everything in this world. The Ultimate Goal of IOT is to Automate Human Life. In this way, IoT creates a relationship among people-people, people-things, and things-things.

Applications of IoT

Wearables (like Smartwatches to track health and exercise progress, sleep patterns, send text messages and calls).

Smart Home (hundreds of products in the market that users can control even with their voices).

Smart Cities (solves traffic congestion issues, smart parking, reduces noise, crime, and pollution).

Connected Cars (to assist drivers and reduce accidents).

Internet of Things Devices & Examples

Amazon Echo - Smart Home: The Amazon Echo works through its voice assistant, Alexa, which users can talk to in order to perform a variety of functions. Users can tell Alexa to play music, provide a weather report, get sports scores, order an Uber, and more.

Fitbit One - Wearables: The Fitbit One tracks your steps, floors climbed, calories burned, and sleep quality. The device also wirelessly syncs with computers and smartphones in order to transmit your fitness data in understandable charts to monitor your progress.

Barcelona - Smart Cities: The Spanish city is one of the foremost smart cities in the world after it implemented several IoT initiatives that have helped enhance smart parking and the environment.

AT&T - Connected Car: AT&T added 1.3 million cars to its network in the second quarter of 2016, bringing the total number of cars it connects to 9.5 million. Drivers don't have to subscribe or pay a monthly fee for data in order for AT&T to count them as subscribers.

Other articles on IoT:

Real World Examples of IoT (Internet of Things) - How will IoT change our lives?