What is Java? Presentation On Introduction To Core Java By PSK Technologies (1)

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INTRODUCTION TOCORE JAVA

• PSK TECHNOLOGIES
• An ISO 90012015 (QMS) Certified IT Company
  Computer Education Software Development
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• Plot No-780, Near Durga Temple, Katol Road
  Chaoni, Nagpur-13
• Phone [phone]
• Email info_at_psktechnologies.co.in
• website www.pskitservices.com

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• CONTENT

• History
• Several Java Version
• Feature of java
• Internal Detail
• JVM
• What is JVM
• Variables
• Data Type in java
• Advantages of naming Convention in java

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• HISTORY Java is a general, all-purpose computer
  programming language that is circumstantial,
  class-based, object-oriented, and specially
  designed to have few application dependencies as
  possible. Java was developed initially for
  interactive television, but it was too advanced
  technology for the digital cable television
  industry at the time. It is proposed to let
  application developers write once, run anywhere,
  suggesting that compiled Java code can run on all
  platforms that condone Java without the necessity
  to recompile. Java applications are compiled to
  byte code that can run on any Java virtual
  machine (JVM) regardless of computer
  architecture.
• James Gosling is generally credited as inventor
  of the Java programming language

• First version released in 1995,Several java
  versions have been released, and they are
• JDK Alpha and Beta (1995)
• JDK 1.0 (23rd Jan 1996)
• JDK 1.1 (19th Feb 1997)
• J2SE 1.2 (8th Dec 1998)
• J2SE 1.3 (8th May 2000)
• J2SE 1.4 (6th Feb 2002)
• J2SE 5.0 (30th Sep 2004)
• Java SE 6 (11th Dec 2006)
• Java SE 7 (28th July 2011)
• Java SE 8 (18th March 2014)
• Java SE 9 (21st Sep 2017)
• Java SE 10 (20th March 2018)

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• FEATURES OF JAVAThe following are some important
  features of Java Programming Language

• Simple
• Platform Independent
• Architectural Neutral
• Dynamic and Extensible
• Portable
• Multi-Threading
• Distributed
• Networked
• Secured
• High Performance

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• Internal Details of Hello Java Program
• What happens at compile time?At compile time,
  java file is compiled by Java Compiler (It does
  not interact with OS) and converts the java code
  into byte code.
  
• 
  
• 
  Java Virtual Machine(JVM)
• What happens At runtime ?
• At runtime, following steps are performed
• Class Loader Is the subsystem of JVM that is
  used to load class files
• Byte Code Verifier Checks the code fragments for
  illegal code that can violate access right to
  objects.
• Interpreter Read byte code stream then execute
  the instructions.

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• IMPORTANT DEFINATION
• Class Keyword is used to declare a class in
  java.
• Public Keyword is an access modifier which
  represents visibility, it means it is visible to
  all.
• Static Is a keyword, if we declare any method
  as static, it is known as static method. The
  core advantage of static method is that there
  is no need to create object to invoke the
  static method. The main method is executed by the
  JVM, so it doesn't require to create object
  to invoke the main method. So it saves memory.
• Void Is the return type of the method, it
  means it doesn't return any value.
• Main Represents startup of the program.

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• Valid java main method signature
• public static void main(String args)
• public static void main(String args)
• public static void main(String args)
• public static void main(String... args)
• static public void main(String args)
• public static final void main(String args)
• final public static void main(String args)
• Final strictfp public static void main(String
  args)

• Invalid java main method signature
• public void main(String args)
• static void main(String args)
• public void static main(String args)
• abstract public static void main(String args)

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• What is JDK, JRE and JVM
• Understanding the difference between JDK, JRE and
  JVM is important in Java. We are having brief
  overview of JVM here.
• JVM
• JVM (Java Virtual Machine) is an abstract
  machine. It is a specification that provides
  runtime environment in which java byte code can
  be executed. JVM (Java Virtual Machine) is an
  abstract machine. It is a specification that
  provides runtime environment in which java byte
  code can be executed.
•  The JVM performs following main tasks
• Loads code
• Verifies code
• Executes code
• Provides runtime environment

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• JRE
• JRE is an acronym for Java Runtime Environment.
  It is used to provide runtime environment. It is
  the implementation of JVM. It physically exists.
  It contains set of libraries other files that
  JVM uses at runtime. Implementation of JVMs are
  also actively released by other companies Sun
  Micro Systems.

• JDK
• JDK is an acronym for Java Development Kit. It
  physically exists. It contains JRE development
  tools.

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• JVM (Java Virtual Machine)
• JVM (Java Virtual Machine) is an abstract
  machine. It is a specification that provides
  runtime environment in which java byte code can
  be executed. JVMs are available for many hardware
  and software platforms (i.e. JVM is platform
  dependent).
• What is JVM
• It is A specification where working of Java
  Virtual Machine is specified. But implementation
  provider is independent to choose the algorithm.
  Its implementation has been provided by Sun and
  other companies.
• An implementation its implementation is known as
  JRE (Java Runtime Environment).
• Runtime Instance Whenever you write java command
  on the command prompt to run the java class, and
  instance of JVM is created.

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• What JVM does?
• The JVM performs following operation
• Loads code
• Verifies code
• Executes code
• Provides runtime environment
• JVM provides definitions for the
• Memory area
• Class file format
• Register set
• Garbage-collected heap
• Fatal error reporting etc.

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• Internal Architecture of JVM
• Let's understand the internal architecture of
  JVM. It contains class loader, memory area,
  execution engine etc. it Contain

• Class loader
• Class loader is a subsystem of JVM that is used
  to load class files.
• Class (Method) Area
• Class (Method) Area stores per-class structures
  such as the runtime constant pool, field and
  method data, the code for methods.
• Heap
• It is the runtime data area in which objects are
  allocated.

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• Stack
• Java Stack stores frames. It holds local
  variables and partial results, and plays a part
  in method invocation and return.
• Each thread has a private JVM stack, created at
  the same time as thread.
• A new frame is created each time a method is
  invoked. A frame is destroyed when its method
  invocation completes.
• Program Counter Register
• PC (program counter) register. It contains the
  address of the Java virtual machine instruction
  currently being executed.
• Native Method Stack
• It contains all the native methods used in the
  application.
• Execution Engine
• A virtual processor
• Interpreter Read byte code stream then execute
  the instructions.
• Just-In-Time (JIT) compiler It is used to
  improve the performance. JIT compiles parts of
  the byte code that have similar functionality at
  the same time, and hence reduces the amount of
  time needed for compilation. Here the term?
  Compiler? Refers to a translator from the
  instruction set of a Java virtual machine (JVM)
  to the instruction set of a specific CPU.

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• Variable
• Variable is name of reserved area allocated in
  memory.

• Types of Variable
• There are three types of variables in java
• local variable
• instance variable
• static variable

 

• Local Variable
• A variable that is declared inside the method is
  called local variable.
• Instance Variable
• A variable that is declared inside the class but
  outside the method is called instance variable.
  It is not declared as static.
• Static variable
• A variable that is declared as static is called
  static variable. It cannot be local.

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• Data Types in Java
• In java, there are two types of data types
• Primitive data types
• Non-primitive data types

Data Type Default Value Default Size
Boolean false 1 bit
Char '\u0000' 2 byte
Byte 0 1 byte
Short 0 2 byte
Int 0 4 byte
Long 0L 8 byte
Float 0.0f 4 byte
Double 0.0d 8 byte
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• Advantage of naming conventions in java
• By using standard Java naming conventions, you
  make your code easier to read for yourself and
  for other programmers. Readability of Java
  program is very important. It indicates that less
  time is spent to figure out what the code does.

Name Convention
Class name Should start with uppercase letter and be a noun e.g. String , color Button, System, Thread etc.
interface name should start with uppercase letter and be an adjective e.g. Runnable, Remote, Action Listener etc.
method name should start with lowercase letter and be a verb e.g. action Performed(), main(), print(), println() etc.
variable name should start with lowercase letter e.g. first Name, order Number etc.
package name should be in lowercase letter e.g. java, Lang, sql, until etc.
constants name Should be in uppercase letter. e.g. RED, YELLOW, MAX_PRIORITY etc.
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