Design Pattern Walkthrough

The term Design Pattern is a buzzword in the software development world. Actually, we can develop software even without a design pattern, but software development is a continuous process, changes come and the software should adapt to the changes. So, if the software is developed without any consideration of the design pattern, then it is difficult to scale and maintain. Also, if design patterns are properly used, it's very easy to understand your code to other developers. A design pattern is nothing, but the adapted practices by experienced software developers, so it is a good idea to consider design patterns while we develop software.

Basically, we can divide the design pattern into the following categories:

A. Creational Design Pattern

B. Structural Design Pattern

C. Behavioural Design Pattern

D. J2EE Design Pattern (Only for Java)

A. Creational Design Pattern

1) Singleton

2) Factory

3) Abstract Factory 

4) Builder

5) Prototype 

B. Structural Design Pattern

1) Adapter 

2) Decorator

3) Bridge

4) Composite

5) Facade 

6) Flyweight 

7) Proxy

C. Behavioural Design Pattern

1) Command

2) Observer

3) Iterator

4) Memento

5) Template

6) State

7) Strategy

8) Visitor

9) Mediator 

10) Chain of Responsibility

D. J2EE Design Pattern

Create USB Windows 10 Installer in Ubuntu System

 As the title clearly says, creating bootable USB in the Ubuntu system is a bit challenging as compared to the Windows system. Windows system provided their own tool and we can seamlessly create a bootable thumb drive. After the less availability of CD ROMs, it is very important to know how to create bootable USB disks. 

Yes, I also tried to use some of the tools I was familiar with, such as UnetBootIn, copying with dd tool, etc, but unfortunately, I was unsuccessful. It creates a bootable USB, but the problem, the installation of windows crashes, with some file related error. 

Because I did not have any windows system in my machines, and I have to install windows in my newly bought notebook, I have to create anyhow a bootable Windows 10 installer using my Linux machine. I carried out some research on this, got a working tool to create a bootable Windows installer on USB.

1) Installation of WOEUSB command

What I did is, I have first of all run a couple of Linux commands to add the repository, then install the tool.

sudo add-apt-repository ppa:nilarimogard/webupd8

sudo apt udpate

sudo apt intall woeusb

Now installation completes. 

2) Get USB Info

We have to find out the usb device id (for example: /dev/sdb or /dev/sdc). Using one of the following commands, we can find out that information:

sudo fdisk -l

lsblk 

3) Unmount the USB Disk

This is important, we have to unmount the USB before carrying out the problem. There is a simple command to carry out this task:

sudo umount /dev/sdb1

3) Create the installer 

The final step is to run a command to create the actual installer. 

sudo woeusb --target-filesystem NTFS --device Win10_2004_English_x64.iso /dev/sdb

Here, Win10_2004_English_x64.iso is the iso file downloaded from the Microsoft site. Which can be freely downloaded. 

/dev/sdb is the path of the USB disk.

It can take up to 5-6 minutes depending upon how fast your system is.

After the process finishes, we are ready to use it as a windows 10 installer. 

Creating multipurpose executable Jar file

As the title says, this recipe is focused on creating a multipurpose jar file, where a single jar file can be used for multiple requirements. I am going to cover the whole process by diving into the following steps:
1) Create a Java application
2) Bundling into an executable Jar file
3) Running a Jar file

I take a problem scenario to explain the above steps and how they are carried out.

Problem:
We want to have a java application, which should have addition, subtraction, multiplication and division functionalities,  that we can call those functionalities providing the command line parameters. For example

add 2 4 4 (result=2+4+4)
subtract 54 12  (result=54+12)
multiply 12 54 55 (result=12*54*55)
divide 34 17 (result=34/17)


So, let's start:
1) Create a Java application
I am creating a Java application with Gradle as a build tool because it is easy to use. I am creating 4 classes with the main method which is responsible for corresponding operation and parameters. One option could be to create a single method and get an operation as a parameter, which makes it really complex to handle parameters. If we create a main method for each operation, it makes our tasks of handling parameters easy.

So, I begin with creating four java classes with main method, which manipulates the arguments to get the corresponding result. Because the example task is very simple, our actual task could be way bigger with many dependent libraries. So, we define a bunch of libraries in "build.gradle" file and we create a "fatJar" with all dependencies included in the jar file. An alternative will be we copy dependent libraries in the classpath.

I begin with the fatJar method, which create a jar file with all dependent libraries automatically from gradle. For this, we have to write a method to create fatJar. Have a look at the sample build.gradle file.

File: build.gradle



settings.gradle



The method jar create the jar file without dependencies. But the fatJar create a jar file with all dependencies, and we can use out of the box.

So, after definition of Gradle build information.

Now, we create class files with specific operation in main methods. The class files look something like this:

Add.java



Subtract.java



Multiply.java



Division.java



The application structure looks like this:



So far, we have created a java application with the required operations.


2) Bundling into an executable Jar file

Bundling into an executable Jar file is quite easy because we have already written a method in build.gradle file above. So, we just call

gradle clean && gradle fatJar

The created Jar file will be in folder build/libs as shown above(Operations.jar)

Note: If we simply run "gradle build", then it will create a thin jar file(i.e. without dependencies)


3) Running a Jar file

The Last Step is to execute the Jar file Operations.jar. The bundled jar file includes all the classes, and we can run all operations providing corresponding arguments.
For example:
java -cp Operations.jar com.kpaudel.operations.Add 12 34.33 45.3

Result=91.63

Similarly, we can check all other operations providing the parameters. 

java -cp Operations.jar com.kpaudel.operations.Subtract 123.56 23

Result=100.56

java -cp Operations.jar com.kpaudel.operations.Multiply 12.2 34.5

Result=420.9

java -cp Operations.jar com.kpaudel.operations.Division 12 2 2

Result=3.0

So, we can independently manage each operation with their own arguments, which makes very easy to handle input arguments. Apart from this advantage, bundling into a single jar file makes it easy to deploy, which means only a single jar file with many operations can be called separately.

I am using this method to create download and upload operations for my cloud storage, getting advantage of using the same jar file for different purposes of download and upload operations(with independent input parameters.) 

I hope you have enjoyed this recipe.  Thanks for reading :)