DEV Community: Naveen kumar

Variable in java

Naveen kumar — Wed, 11 Feb 2026 05:41:36 +0000

Java Variable

Variable is a container it stores data in memory. Each variable has a name, data type and a value.
**Variable is a name of memory allocation
Variable name should start with small letter.
*It is Case-sensitive.
*The type of data that can be stored in a variable is defined by data type.

It is stored in Stack memory.
**Ex*
int value = 27;
int-> data type
value-> variable name
= -> assignment operator
27 -> data
; -> end of statement

// Declaration and Assignment in different line:
int count; // Declaration
count = 20; // Assignment of a value

//Declared and initialized in one line:
int value = 30;
String class = "Naveen";

Data types

Naveen kumar — Thu, 29 Jan 2026 15:36:54 +0000

Data types

Data types is kind of size and value can be stored in data (like Numbers, character, true/false etc..)
There are two types of data types

i) Primitive data type
ii) Non - primitive data type

i. Primitive date type

Byte - 1 byte
Sort - 2 byte
Int - 4 byte
Long - 8 byte
Float - 2 byte
Double. - 4 byte
Char. - 1 byte
Boolean - 1 bit

1 bit = 8 bit

Range of primitive data types

Byte - 1 byte - 8 bit
Sort - 2 byte - 16 bit
Int - 4 byte - 32 bit
Long - 8 byte _ 64 bit
Float. - 2 byte - 16 bit
Double. - 4 byte -16 bit
Char. - 1 byte - 8 bit
Boolean - 1 bit- 1 bit

Non - primitive Data types

String
1)The values of the strings can store in between " " (double quotation)
2)string allows only can store the variable of name.
Eg.- String "Naveen"
3) String stores the multiple char " "

Class and Object

Naveen kumar — Thu, 29 Jan 2026 15:02:04 +0000

Class:-

Class is a java keyword
Class is a template
Class is logical entity
Class name First letter should be the capital letter
Eg. StudentName
Class name should allow only these special characters like ($ & _)..( starting, intermediate and last)
Class name should allows only numeric value like ( intermediate and last)

Syntax:
Class BikeShowroom
{
Code
}

OBJECT

Object is a State and Behaviour
Object is physical entity
Object is used to store State and behaviour

Syntax
BikeShowroom ref = new BikeShowroom();

New is a keyword of java

If we create a object, jvm will allocate a memory in heap at runtime

Day 2..JRE ( jvm)

Naveen kumar — Fri, 23 Jan 2026 11:18:01 +0000

JDK - Java development kit
JRE -(Java Runtime Environment)
JRE is a kind of Library
1. It will help to run the java program
2. without syntax error it will work as a .Classfile s
3. JRE contains many java files
4. It used to keep many java files

JVM..( Java Virtual Machine)

It helps to create the memory allocation
Then the file will move to JIT as a.class file

JIT - Just In Time

It is used to convert the code to understand the system language like as Binary code(Just In Time) Binary code(010101)

Day 1.. JDK introduction

Naveen kumar — Wed, 21 Jan 2026 11:42:23 +0000

JDK -

JDK is a Java development kit( software development kit)
Provided by oracle.
It helps to convert .java file into .class file
It helps to compile the java program
JDK is a platform independent why because it can support any kind of OS/Linux/Mac & processor
If we write the java code program,Jdk will check the error.
If it's correct it will convert into .class file format.
Otherwise it will show the error
Eg. Error --> 3rd line error
Correct --> it will give .class file
It's is used to develop a Java applications

.java file is a readable file
.class file is a unreadable file

Compilation ---steps
1)Cmd --> java--version ( to find the JDK version) which is we installed
2) compiler -->> javac Student.java
Eg. Javac filename.java

Example :-
student.java ---student.class file
.class file is an unreadable file.