Understanding Networking and Server Visualization

Introduction to Virtualization
Virtualization and Cloud Computing are not same. Its a component of Cloud Computing.

In virtualization there is a separation of OS with the underlying H/W where as in Cloud Computing (CC), there is a separation of Application from the underlying hardware.

• Earlier, OS’s are installed directly on the hardware.
• Virtualization gives a layer of hypervisor, on which an “instances” of OS runs.
• install a hypervisor layer and then install the “Guest OS”
• Can literally move (copy an image and paste) one instance of OS from one server to another without any installation!!
• Also, multiple instances of OS can be installed on hypervisor

Type 1 Hypervisor (Native or Bare Metal) : A physical machine, and hypervisor on it.

Type 2 Hosted hypervisor : Comp. with an OS, and onto that hypervisor is installed eg :VMWare (installed according to the OS). Onto it guest OS are installed

Hosted solutions (Proprietary ones) on Amazon Cloud etc.

you need a management console to interact with hypervisor(once the physical server has an IP address). With the management console, you can move the instances of OS’s among different physical servers.

Also, according to resource needs, management console can migrate (or turn on and off) based on loads (balances the electricity consumption)

If the physical hardware running the hypervisor fails, management console can quickly migrate the OS to another hardware.

Over Allocation :  static (RAM is split between all the OS instances) and
dynamic (logical allocation more than the physical)

Most of the hypervisor software are free (most of them based on XEN) but they charge for the management console software.

Careful with type 2 Hypervisor : Be careful of the resource allocation. if 4 GB’s of RAM is allocated, the type 2 virtualization hypervisor will take all 4 GB and allocate to the VM even if its not needed. Can crash host OS by overallocating its hardware resources.

1. final
   • constant –> modifier (can’t be changed once declared)
   • a method –> no over riding in child class
   • a class –> no extend (inheritance), no child class
2. finally (Associated with try catch block)
   • try {keep risky code}
   • catch (Exception e) {Handling Code}
   • finally {Clean up code}
3. finalize() : Method in Object Class
   • Always invoked by Garbage Collector just before destroying the object
   • to perform cleanup activities (like database connection close, socket close)
4. *** finally cleanup activities for try catch, finalize() cleanup activities for related to objects.

1. String objects are immutable (every equality with string object creates a new object)
   • String a = “Nitin”; a.concate(Chaurasia);
   • sop(a);// Nitin
   • 2 strings are created (Nitin and Nitin Chaurasia). NC not referenced
2. StringBuffer objects are mutable
   • StringBuffer sb = new StringBuffer(“Nitin”);
   • sb.append(“Chaurasia”)
   • sop(sb);//nitin chaurasia
3. StringBuffer (since java 1.0)
   • Synchronized, thus thread safe, thus low performance (only one thread operates on the object at a time, others has to wait)
4. StringBuilder (from 1.5)
   • same as StringBuffer (constructors and methods) except…
   • non-synchronized, thus no thread safety, thus Relatively high performance.
5. Conclusion :
   • String : fixed content (wont change frequently)
   • StringBuffer : content not fixed and thread safety is required.
   • StringBuilder : content not fixed and thread safety is NOT required.

1. == reference comparison (address comparison)
2.  .equals() is used for content comparison (in general). Can be overridden to comp. ref. if needed
3. All Wrapper Classes + String Classes, .equals() is overridden for content comparison

Modifiers in java : https://www.youtube.com/watch?v=1MmietzIteA&list=PLYPjPMiw3_YsVockWfuuhoP86YPDUXp4f&index=4

Anything can be declared inside anything!!

• Access Specifiers (public, private, protected and <default>) vs Access Modifiers
• Old language constructs… In java there is no terminology. All (12) are considered and modifiers

Interface vs Abstract vs Concrete class

1. Interface (100% abstraction): No idea of implementation, just requirement spoecification, eg. Servlet
   • All methods must be public abstract
2. Abstract : Partial implementation
   • concrete classes can be written
3. Concrete Class : Ready to use service

Class MySystem{
static string out = “nitin”;
}
MySystem.out.length(); //Compare it to
System.out.println(out);

• System is a Class
• out is a static variable of type PrintStream in System class
• println() is a method present in PrintStream.

• Main method name can be set to a desired name by configuring JVM [JVM Customization]

JVM {
public static void nitin(String[] a)
}

• public : to be called by JVM from anywhere
• static : even without existing Object, JVM can call the main method. Also main method is not related to any object.
• void : no return to JVM.
• main : configured JVM
• String[] args : command line argument.
• overloading is possible (PSVM (int b)), but JVM will only call string args method (method hiding)
• Inheritance is also applicable. the JVM first search main in child class or else it will execute the main method from the parent class.
• If both Parent and child methods are same and “static”, this is method hiding… not overriding (only child class method is executed). Appears that overriding is applicable, but because of the static nature, its method hiding.
  • Inheritance and overloading is applicable
  • overriding is not, instead method hiding.
• Java 1.7 enhancements
  • earlier “NoSuchMethodError : main”, now a more meaningful error
  • main method is mendatory, even though class has static block. Before, static block will be executed (and if System.exit(0), the program will terminate as well), and then NoSuchMethodError will be flashed.
  • if both static block followed by main method is present, then everything works as normal in both cases
  • Thus without even writing main, until Java 1.6, something can be printed on the console. from 1.7 onwards, main in compulsory.

• Overloading
  • methods same name but different argument.
  • Compile time polymorphism, static polymorphism, early binding.
  • Method resolution is done by compiler based on reference type
• Overriding :
  • When child class redefinition different than parent class (eg: marriage() method in example)
  • Runtime polymorphism, dynamic polymorphism, late binding
  • Method resolution is done by JVM based on runtime onject
  • co-varient return types are allowed (return can be same as Parent’s method, after Java 1.5)

*** In overloading check only method name (same) and argument type (different, at least order). Return types, access modifiers are not required.

**** In overriding: EVERYTHING should be same.

• Parent p = new Child();
  • can invoke only parents methods
  • can use parent reference to hold any child class object.
  • polymorphism call

• Child c = new Child();
  • can invoke both parent and child methods
  • can hold only child type of object
  • non polymorphic call

• Control Flow in try catch block
  • (after jumping from try, rest of statements of try wont be executed. Thus keep the length of try block be be as small as possible)
  • there may be chances of exception in catch or finally block as well, and it will then be an abnormal termination.
  • if no exception, try and finally will execute
  • if abnornal termination due to exception in try or catch block, then also finally will execute.
• Throwable (Class) has two child classes
  • Exception
    • Programming faults
    • Recoverable (file not found, catch {use local file and continue..})
  • Error
    • lack of system resources (out of memory etc)
    • system admin or server admin is responsible to increase heap memory
    • Non recoverable

• Checked Exception :
  • Checked by compiler for smooth execution of the program at runtime (Menmonics : HallTicketMissingException, PenNotWorkingException, FileNotFoundException)
  • if programmer doesn’t handle checked exceptions, compile time error.
  • Mush be caught (try catch) or thrown (throws clause in the method definition)
  • Throwable -> Exception ->)Runtime exception and its child classes, (Throwable->)Error and its child classes are unchecked exceptions. Rest all are checked.
  • Further classified as fully checked or partially checked
• Unchecked Exception
  • not checked by Compiler (bonmBlast exception, arithmatic, nullpointer)
  • Compiler won’t check if the programmer handled the exception.

*** Both occur at runtime.

• FullyChecked exception
  • iff all the child classes are checked
• PrtiallyChecked exception
  • if some of child classes are Unchecked
  • Only possible partially checked in Java
    1. Exception
    2. Throwable

Java Multithreading

• Multitasking
  1. Process based multitasking (typing program while listening to music from the same system) Eack task is separate independent process(OS level)
  2. Thread based multitasking Separate independent task of same program (Programmer based)
• Java Threading
  • strong API Support
  • 2 ways of defining
    1. By extending Thread class
       • override run() method;
       • everything within run() is called a job.
       • after instantiating t.start(), job from run() begins
       • both main thread and child thread runs simultaneously
       • no fixed flow of execution between main and child
       • Thread scheduler is part of JVM
    2. By implementing Runnable Interface (in java.lang and only method is run()) (Best approach)
       • class A implements Runnable{ public void run(){ … }
       • after instantiating, Thread t = new Thread(target Runnable object) and t.start();
• Thread Life cycle

For Free portfolio pictures : https://unsplash.com
Online Photo Editing  : http://www.picmonkey.com
Online Logo Editing : http://logomakr.com
The Logo/icons site : http://thenounproject.com/

Theme : Vantage

Plugins :

1. Page Builder, for visual addition of html elements.
2. LightBox Plus ColorBox : Lightbox Plus Colorbox permits users to view larger versions of images without having to leave the current page.
3.  Black Studio Tiny MCE : For feature rich text editor
4. Contact Form 7 :

Widget:

1. Social Media Widget

Themify Builder : Stumbled upon themify builder as a part of Theme customization for wordpress 2013 theme. The tool is great to define a layout by drag and drop feature. Also Theme customization  and why child theme is created was understood with theses videos.

https://www.youtube.com/watch?v=giawHh0RztI

Themify Builder

https://www.youtube.com/watch?v=_AsoMMYqf_g

• Inspired by 5 stages of Dreyfus Model of Skill Acquisition.
• Novices, Advanced Beginner, Competent, Proficient, Expert
• Step 1 : Learning to write codes less than 10 lines, but inclusive good logic. Gave me a good practice to set my hands on Java without using Google or any IDE. Writing logic of a method without bothering about the execution of a fully functional program. Also Test cases teaches the faults in the logic. The site takes away the burden of setting/installing Java or any other IDE’s. In short :

It teaches Thinking in Java

Taking Baby Steps CodingBat.

• Step 2 : Learning to write fully functional programs (with 3 to 4 classes), with object creation, keeping in mind when to use static etc. JAVA 101 type assignments, which gives a clue of how the language is used to solve problems. A brief overview on OOP.
  • Assignment 1 :(Based on) Class String, Keyboard input, Console output
  • Assignment 2 : Defining Classes and methods, Encapsulation, boolean if & switch
  • Assignment 3 : Loops and Math. Random(), Objects and References (equals, toString())
  • Assignment 4 : Constructors, Static variables & methods, Overloading
  • Assignment 5 : Aggregation, exceptions
  • Assignment 6 : File Handling and Arrays

• Step 3 : Learning Object Oriented Concepts (Later)
• Step 4: Practice of elementary concepts of Collections from BJP

Strings, Arrays uses for loop as cursor

Arralylist, LinkedList, Vector and Stack uses ListIterator (most powerful Cursor)

All Collections use Iterator as Cursor

The Divide and Conquer Approach

1. Divide the problem into Subproblems that are smaller instances of the same problem.
2. Conquer the subproblem by solving them recursively. Use “base case” for the simplest subproblem. (Recursion is bottom up)
3. Combine the solutions to the subproblems into the solution for the original problem.

Divide and Conquer usually generates brand-new problem at each step of recursion.

Elements of Dynamic Programming

For any optimization Problem, to be considered for the Dynamic Programming Problem, TWO key elements are needed.

1. Optimal substructure : Problem exhibits optimal substructure, and optimal solution is built from optimal solutions to subproblem.
2. Overlapping subproblems : space of subproblems must be small. The total number of distinct subproblems is polynomial in the input size.

Dynamic programming algorithm typically take advantage of overlapping subproblem by solving each subproblem once and then storing the solution in a table where it can be looked up when needed.

A bottom-up dynamic-programming algorithm usually outperforms the corresponding top-down memoized algorithm by a constant factor, because the bottom-up algorithm has no overhead for recursion and less overhead for maintaining the table.

Elements of Greedy Strategy

A greedy algorithm makes choice that seems best at the moment.

This heuristic strategy does not always produce an optimal solution but sometimes it does.

1. Determine the optimal substructure of the problem.
2. Develop a recursive solution.
3. Show that if we make the greedy choice, then only one subproblem remains.
4. Prove that it is always safe to make the greedy choice. (Steps 3 and 4 can occur in either order.)
5. Develop a recursive algorithm that implements the greedy strategy.
6. Convert the recursive algorithm to an iterative algorithm.

Place .gitignore file in the project’s root directory. (It can be version-ed). The .git/info/exclude can be configured to ignore personal project settings. The .git folder carries settings adjusted for the local user.

git config credential.helper store
git push -u origin master
Username:
Password:

Git will then not ask for username and password again and again.

The GIT Primer

Pulling a fresh Project from a repository first time

git fetch (to sync the project between different machines)

Create a file -> Add the file to staging area by commit –> modify the file and  add the file to staging area commit and –> Push

git clone https://nitinc@bitbucket.org/nitinc/eclipseinitialtest.git (for HTTPS…easier and more intuitive!!)

git log (shows all committed logs…AFTER CLONING)
git branch (showed only master…not r2….SEE)

DO GLOBAL GIT SETTINGS (for commits to recognize you)
git config –global user.name “Nitin Chaurasia VM”
git config –global user.email nitinc@bgsu.edu
git config –global color.ui tru

• Switch –> Firewall –> Router –> Modem ———->INTERNET!!
• Switch has Wireless Access Points (WAP) to allow wireless devices to be connected to it, and various computers are connected physically through wires to the switch.
• Physical v/s Logical connection -> within a switch we can have logical connection.
• Speed –> 12Mbps = 1.5 MBps (vendors talk in terms of bits to make it look bigger, divide by 8 and check)

The Modem

converts the signals into