core java important notes for interview.


This article talks about important and basic concepts in core java language. The entire core java language runs on the basis of these concepts. Core java language is currently use for programming in almost 99% machines. Due to this, the demand of this language has increased in the technical and IT sector. In this, Advance Java is also an advanced language after core java, let’s learn about this in the next few articles. Many hundreds of students have study this programming language and got place in big IT companies. Also, companies are offering good packages to students.

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[  Table of Content.

History of Core Java.


Programming Language core java.

  1. Low level language.

  2. Mid level language.

  3. High level language.

3.1 Source File.

3.2 Complier.

3.4 Interpretor.

Important Features Core Java.

1. Source File.

2. Javac.

3. Byte code.


What is JDK, JRE and JVM in core java?

How develop source code?

Command Prompt.

User home directory.

Current Directory.


Mkdir or MD.




Creat Complie and Execute in core java. ]


History of Core Java

  • Core Java was developed by James Gosling along with his team. James Gosling is called as the father of Java.
  • Java was developed in the year 1995. Java was initially started in the early 1991 and he took 4 years to develop.
  • The intention to develop Java is to control the embedded system like set of box, AC, Television etc…..
  • When Java was developed it was to advance language. So James Gosling as decided to make Java used in developing the application. By using Java we can developed any kind of application link. (a) Stand alone App, (b) web App, (c) Mobile or Desktop App, (d) Business App.


  • Language is a media to communicate and share our feeling with others.

Programming Language core java.

  • Programming language consist of set of institutions which are used to communicate with the system to perform some task.
  • Programming language is classified into three types

      1.Low level language.

  • It is also known as machine understandable language. The language which is easily understandable by the system or machine is known as low level language
  • Machine will understand only binary language. i.e. 0 and 1
  • For a machine it is very match understand binary language. But for a programmer it is not quite easy to instruct the system.
  • i.e. the reason will mid level language has been discovered.

      2. Mid level language.

mid level language

  • It is also known as assembly level language
  • This mid level language consist of some predefined words. Each and every predefined words is assigned with some specific task.
  • This predefined words is also known as a nemenonics.
  • In mid level language we have a translator called assembler. Which is used to convert mid level instructions to binary from.

( Note.

  • By using this mid level language we can perform only arithmetic operations. We can’t develop huge application link Flipkart, Amazon, Facebook etc..
  • i.e. the reason while we are making use of high level language. )

     3. High level language.

high level language

  • Example of high level language = C, C++, Core Java, Payton, .net, Java Script, HTML, CSS.
  • The language which is easy from programmer to right the instructions, understand, execute is known as high level language.
  • By using this high level language we can develop any kind of application. For a programmer it is very much easier to instruct the system using high level language.

     3.1) Source File.

  •   Source file consist of set of institutions which are wright high level language.

     3.2) Complier.

  • Complier is a software which is use to convert source file to machine understandable language at once.

     3.3) Interpretor.

  • Interpretor is a software which is use to convert source file to machine understandable language line by line.

Important Features Core Java.

Platform Dependent.

core java platform dependent

  • If an application is develop using a particular platform and that application will be exicutable only on that particular platform, This is call as Platform Dependent.
  • If an application is develop on a particular platform suppose windows 64-bit-os, which is call as source file.
  • When we give the source file as an input to the Complier, Complier will generate and executable file. This executable file is generate base on the system configuration file (windows 64-bit). This executable file will be execute only on that specified configrate system. This is nothing but platform Dependent.

Platform Independent.

core java platform independant

  • If an application or a source file is develop using a system and that application can be executable an any of the system, this is call as Platform Independent.
  • If a source file is a develop by using specific system (windows 64-bit) and that source file is given as a input to the java compiler, our java Complier will generate and intermediate coed called as byte code. This byte code will be executable on any of the system were JRE is install.

Source File

  • The file which contains set of institutions return in Java language is call as Java source file.
  • It will be the extraction of Java.


  • Javac stand for java compiler which is use to convert source file to intermediate coed call as byte code.

Byte code.

  • Byte code is call as intermediate code which is natural understandable by the programmer nor by the machine or system.
  • Byte code will be .class extension.


  • Interpreter is use to convert byte code to machine understandable language or binary language or mid level language.

( Note.

  • Java is hence platform Independent but JRE is dependent. Without JRE it is impossible to execute byte code on the system. )

What is JDK, JRE and JVM in core java?


core java JDK

  • JDK stands for java development kit which is a complaint package use to develop the code and execute the code. JDK consist of Java-c (Java Compiler) and JRE.


core java JRE

  • JRE stands for for java runtime environment which is use to execute the code.
  • JRE consist of JVM along with some inbuilt library function.

( Note

  • JRE along is available in the Internet.
  • If we installed JRE software than we can’t develop any code. We can only able to execute the code. )


core java JVM

  • JVM stands for Java virtual machine.
  • JVM is use to convert byte code to machine understandable language.
  • JVM consist of JIT Complier, Class loder etc……
  • JIT stands for Just-IN-Time Complier (interpreter).

How develop source code?

If you want to develop the source code we need a dedicated in environment. They are types of environment.

      a) Editor’s

  • Example – notepad, notepad++, Editplus etc..
  • The using editor’s we can developed a source code but if you want to execute the source code we need to help of command prompt. by making use of commands we can complied and executed the code.

      b) IDE

  • IDE stands for Integrated development environment.
  • Example – Editpluse, Net Beans, Greem foot, VS code, sub time, etc…….
  • By using IDE we can develop the source code and parallely we can execute also.
  • When we make use of IDE no need to depend on command prompt.

Command Prompt.

  • In windows OS the hard disk is divide into multiple portions. Each and every portion is know as drive. Each drive has a name.

User home directory.

  • Directory means folder
  • A folder which is create inside ‘C’ drive and how’s name is same as user name is know as user home directory.
  • When ever we open command from immediately by default the path is set to user home directory.

Current Directory.

  • The folder which is currently under use is know as current directory or current working directory.


With the help of path we can move from one directory to another directory. Path is classified into two types.
i.e. absolut path and relative path

     (a) Absolut Path.

  • The path which is Starts from drive name is know as absolut path.
  • Example – D:\wccm15\java>
  • Absolut path doesn’t depend on current working directory.

      (b) Relative Path.

  • The path which doesn’t start with drive name is know as relative path. relative path depend’s on current working directory.
  • Example – C:\wccm15\java>.

core java coding

Mkdir or MD.

  • Mkdir or MD stands for make directory. It will create new folder inside current working directory.
  • For this command we should pass folder name as input.


  • CD stands for change directory for this CD command if a pass folder name as input than we can move in forward direction.
  • It you we want to move in backward direction than for the same CD command we should pass (..).


  • Java-c stands for java compiler this command is use to invoke the compiler.
  • For this Java-c we should pass file name with java exception as an input.


  • This command is use to invoke the JRE.
  • For this command we should pass class name as input.

Creat Complie and Execute in core java.

  • Complie – Javac.Filename.Java
  • Example –
  • Execute – Java class name.
  • Example – Java Demo.


  • It is highly recommende for a programmer to privet the file name exactly same as class name.)


The information in this article lets you know how the core java language runs and what are its current benefits. In the following articles, you will be give complete knowledge about java language. how you can crack IT filed interview by studying it. Also coding programs will be provided to you for practice. Keep checking the updates of this page and keep sharing it in your circle of friends. Thank you for visiting.(

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