Category Archives: Java

Java Puzzles to Eliminate Code Fear

A method is a set of code

 

variable
string
return
void
method
String
-equals
-equalsIgnoreCase
-Indexof
-LastIndexOf
-!equals
-String.substring
char
TestingUtils.runTests()
Conditionals

 

Scenario:
We have a loud barking dog. The “hour” parameter is the current hour time in the range 0 to 23. We are in trouble if the hour is before 7 or after 20. Return true if we are in trouble

While Loop:

code:

output:

For Loop:

Reverse character:

Print  even number from 0 to 100:

Sending parameters as an array

Cool recursion example instead of loop:

SpeedingFine Assignment:

my logic:

 

We always try to make the code short and sweet: Logic from the course instructor

Short and sweet code:

 

Another logical problem:

Singing code by me:

Also by ternary operator in one line:

In one line with ternary operator

Ass_06:

Amar VuulVaal code:

 

Valo code FizzyWizzy :P::

Assignment_09 my own solution:

Logic from the instructor:

 

 

 

 

Class Object Example

Class
Object
– Earth is a software application where human and other thing is software objects.For creating object we need to create a human class. Humans have basic behaviors as well as some basic attributes age height inches etc.

 

Human,java

 

 

Earth.java

 

 

Interface Polymorphism Example

Robot.java

 

Human.java

 

Walkable.java it is interface

 

Application.java it is main class to print

Turning Application main class into lambda:

 

 

Java learned as so far:

Java variables,
Array, 2d array
Method
Different method invoking and return type
Class
– Class is actually a blueprint/specification/design
– A class can create as many as objects it needs to create
Object
– Earth is a software application where human and other thing is software objects.For creating object we need to create a human class
– Objects do particular behavior in a class
– Object exist only in application runtime actually when application is running
– Objects have identity,state and behavior

this keyword – it represent current object
Instance
Constructor – The costructor is a special method with the same name as the class and it’s used to instantiate objects from that class
– Every class has a by default constructor if we don’t put it manually
– The constructor is special method containing instructions for object creation. it can be said it is so called birth method. It has instructions for how the object will be born when the application starts up
Static keyword
Stack and heap memory
Garbage collection
Object oriented Programming = better organizing of code, it is a way to organize our code from multiple files by creating objects
Local variable
Reference variable
Instance variable
Inheritance
– Inheritance is the approach to get/transfer behaviour of one class to another
– We use extends keyword for inheriting, in inheritance we inherit from parent class which known as base class and the class which needs inheritation is known as child class or sub class/derived class
super keyword it extract constructor and it’s variable from parent class but reverse is not possible
Overrides
– Same method name with different purpose
– Same method name in parent class but in child class the method name is same but with different purpose
– Overrides means replace
– Override is not a good idea sometimes so we go for interface
Interfaces
– Interface is a contract with a class. The class needs to implements that method of the interface according to contract
– Interface has a method which does not need body, so it is just only to define, it is called as abstract method
– one parent class
– We use implements keyword while putting interface in a class
Abstract class
– When you don’t need all methods to invoke you can use abstract method, you can not make object from abstract class. Abstract method needs to be in abstract class. We use abstract keyword for both method and object to define abstract class and methods
– you can only extend abstract class but can not instantiate abstract class
– We can define abstract class as a type while creating object
Polymorphism

Loops
Exception Handling

Collection Framework
Wrapper class
Threading
Concurrency
Database

Jshell
Functional Interfaces
Lambda expressions

-Lambda helps us to use separate from associated object
– it can run without class
– We need to use lot of interfaces for this

Streams

Ei bold kora jayga diye project banaye banaye clear korte hobe
Italic kora jaygagula motamuti clear asey In Sha Allah, Alhamdulillah
The source is : Imtiaz Ahmed’s complete Java course

 

Master Object Oriented Design in Java course note

Association: It defines relationship between classes, it defines how the software will behave
Dependency Association: For example from code:

A driver receives a vehicle reference only as driver then only he can drive or accelerate

Composition: A particular object . It imply ownership
for example in this code:

Aggregation Association: It does not imply ownership

Here Department to SpanishCourse relation is composite

But Course to Student relationship is not composite because it does not imply ownership a student can take many courses or not

We find this relationship from above diagram, the block diamond and white diamond is the part of UML diagram

Forming Association between objects:

has a relationship in customer .

Now when to stop delivery

Overview of software design:
For example: Hospital Employee Management System
Task of the software:
Hire and Terminate Employees
Print Reports(XML,CSV Formats)

Problem Statement:
Current status of the software

Tips for design:
– You must draw design in paper or whiteboard don’t go to code directly
– Don’t overdesign or overdraw
– We have to develop iteratively but early steps should be kept simple
– Class names should be nouns based on their intention

Single Responsibility Priniciple(SRP): Not all the things in the same class

Don’t repeat yourself(DRY):

Arrow sign always describe that it is depends on that dependency class:

 


DAO=Data Access Object

Single Responsibility Principle Special Notes:
A class should have only one single reason to change

 

Open closed principle sayings about class design:

Classes should be open for extension but closed for modification.

Open Closed Principle and Strategy pattern:
Software modules should be open for extension and closed for modification
In development lifecycle software requirements needs to be constantly pour in. If developed need to change the already made codes the design is fragile. Fragile means broken.

So open closed principle save engineers from fragile design

instanceof operator we used here in the code:
HotelManagementSystem class:

Here it is like a junk drawer

So we will make it changes because it is violating OCP principle. This chamging process is known as Strategy pattern. So let’s do it.

We could also do it with interface class except abstract class

Example after applying Strategy pattern:
Nurse.java

Doctor,java

HospitalManagement.java

 

Employee.java

 

EmergencyRoomProcess.java

To String Tutorial:

DemoToString.java

Dependency Inversion Principle:
Device Manufacturing Company has:

The manufacturing process:
1. Assembly
2. Testing
3. Packaging
4. Storage

GeneralMAnufacturingProcess
UML diagram:

We depend on something in driving like car is stopping by traffic light
Imagine a life every car has different mechanism
Violation of Dependency Inversion Principle
When higher level modules depend on lower level ones succeptible to change
Dangers of coupling:
Tight coupling :

Well design software has single responsibility
This method says high level modules should not depend on lowlevel modules. It should depend on abstractions
Abstract classes and Interfaces don’t change as often as concrete classes/ derivatives
Cohesion means related things together.

This code I tried to run in class inside class but did not worked. Then I downloaded course code and run worked then again I tried to do with my directory structure then it worked.

Quizes from OOP course:
Q1:
Q2: The Dependency Inversion Principle states
Interfaces and abstract classes change far less often the concrete derivatives. Concrete classes should depend on Interfaces and abstract classes because they change less often and are higher level modules

Q3: In general the dependency inversion principle states that code should only depend on things that don’t change often
True
Liskov Substitution Principle:
Subtypes must be substitutable for their basetypes

There are some patterns which is not good known as Anti-pattern:
Here the link can be found


This is a ISA relationship, Nurse and Doctor depends on Employee class. Employee class is Abstract class

When it is adding a substitute teacher who does not work as like a teacher it violates the LISKOV pronciple as per this line of definition: Subtypes must be substitutable for their basetypes

So we changed to a new UML which does not violate LISKOV principle and did the code.

New UML:


Question 1:
The Liskov Substitution principle states, that child classes should not be substitutable in place of their parents.

Interface Segregation Principle:

Fat class is a class which has too many responsibilities.

CustomerTransaction

From Quiz: Main Kotha about Interface Segregation Principle:

This principle does not have to do with the number of dependencies that may exist in an application. The principle simply states that modules should not have dependencies on code they do not use.

If a module does not use functionality from another module, there is no reason to have a direct dependency between them. There should be an abstraction in between to segregate the 2 modules

Dependency Injection: 
When the application is not running there is no object because onbject only available in runtime, you will find only some classes

Tight Coupling:
Cohesion:
A very popular dependency injection implementation is spring framework bundled with spring container.

Dependency injection is

Dependency Injection Using Spring:
Observer Pattern:
The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

One basic UML diagram from wikipedia:

Created one for the course:

Builder Pattern:
When there is so many constructors and tough to handle it. Example codes with some bugs. Will do the solution later.

code example:
user.java

app.java

Factory Pattern:

UML Diagram:

codes:
Vehicle.java

VehicleFactory.java

App.java

VehicleType.java

ElectricCar.java

Car.java

Truck.java

Singleton Design Pattern: It only uses once in an application.

PerformanceStage

Application.java

 

 

Course Source Imtiaz Ahmed Master OOP Design udemy course
Best Book Rereference/Website reference for learning Java: https://beginnersbook.com/2013/12/java-string-equals-and-equalsignorecase-methods-example/

JDBC

JDBC=Java Database Connectivity

ArrayList in Java

ArrayList in Java:

Generics:

 

LinkedList is faster for manipulation but slower for retrieval and ArrayList is slower for manipulation but faster for retrieval

 

My Beautiful Crafted Java OOP

Human.java

Earth.java

 

Started Course: Java In Depth Become a Complete Java Engineer

I have started this course from Udemy and will complete soon with all my effort In Sha Allah:

 

Book Recommendation: Effective Java, Second Edition, Joshua Bloch
Harnessing Java by Kishori Shoron
Head First Java

 

1st video:

Installed JDK
Environment Setup
Made Hello.java with Notepad++
then done javac Hello from cmd:
It made Hello class which is platform independent

2nd Video:

Installing Intellij and Setup for Running Java Application:

Section:3 Classes and Objects

2d Array and 3D array some problem but will clear later now I should move on with other topics.

What is this keyword in OOP

What is “this”?

You may have noticed something slightly strange in our methods. Look at this one for example:

You are probably wondering what “this” is. The this keyword refers to the current object the code is being written inside — so in this case this is equivalent to person.

Java Programming Recap In Sha Allah

OOP concept clearings from some MOOC courses

Code:

Student.java

 


 

StudentTest.java

 

 

 

Overriding vs. Overloading in Java

Overriding code:

output:

Overloading code:

 

Reference:
http://www.programcreek.com/2009/02/overriding-and-overloading-in-java-with-examples/

Java Programmer

CAREER OPPORTUNITY

About Company:
Since its inception in 2000, bdjobs.com has been acknowledged as the most recognized career portal, training center in Bangladesh. Innovative product, dynamic solution & flexibility are core components of bdjobs brand.

Swosti [www.swosti.net], Mobile Credit Card is an offshoot of Bdjobs.com. Swosti, a mBillionth Award-2014 [http://mbillionth.in/] winning concept deals with automated credit and savings management solution in Bangladesh. Now the company invites applications from competent people for the following position(s):

Position : Java Programmer

Educational Requirement:

  • Graduation/ Masters preferably in CSE, Mathematics, Physics, Accounting from any reputed universities.

Qualifications/ Skill:

  • Must have good skill in Java programming
  • Knowledge of Java MVC framework/ Hibernate/ Spring/ GWT/ J2EE/ Eclipse/ JSF/ Oracle/ MySQL/ Tomcat/ iReport/ JMS/ Web Service are needed
  • Experience in Test Code Development
  • Good OOP Knowledge
  • Should be familiar in both operating systems – Linux & Windows
  • Experience in developing Financial Software will be an added advantage
  • 2~3years proven experience is expected
  • Educational qualification will be relaxed for the candidates having strong professional skill.

Preference:

  • Preference will be given to candidates having working experience in development of Android (Mobile based), Financial Applications etc.

Salary: Market-driven

Other Benefits

  • Yearly two festival bonuses (Applicable after 6 months of joining)
  • Performance based yearly salary increment & Profit Sharing
  • Daily refreshment facilities & Lunch benefits
  • Friendly working environment

Apply Instruction:

Application Deadline: June 15, 201

Java Developer

Java/J2EE Developer (EG-560)

We are looking for a Java programmer to join our core team.

Qualificatons

  • Master the Java Language
  • Knowledge of J2EE
  • JMS , JDBC, XML, Web Services – advantage
  • Design Patterns
  • Excellent written and verbal communication skills.

Education

  • University Degree in Computer Science or equivilant.

Experience

  • Minimum 4 years of experience as a Java Developer

To apply for this position, please forward your resume to: [email protected]
Please reference the position number in the Subject field of your email.