Java Variables

Java is a statically typed language, meaning the data type of a variable must be specified at the time of declaration.

Variables in Java are used to store data in memory during the execution of a program.

They provide a way to give names to values so that the program can manipulate these values efficiently.

Declaring Variables:

Variables are declared by specifying the data type followed by the variable name. The syntax for declaring a variable in Java is:

dataType variableName;

For example:

int age;
String name;
double salary;

Assigning Values to Variables:

Once a variable is declared, it can be assigned a value using the assignment operator =.

The syntax for assigning a value to a variable is:

variableName = value;

For example:

age = 30;
name = "John Doe";
salary = 60000.0;

Data Types:

Java supports various data types, including primitive data types (int, double, char, boolean, etc.) and non-primitive data types (String, arrays, objects, etc.).

Primitive Data Types:

  • int : used to store whole numbers (integers).
  • double : used to store decimal numbers (floating-point numbers).
  • char : used to store single characters.
  • boolean : used to store values of true or false.

Non-Primitive Data Types:

  • String : used to store a sequence of characters.
  • arrays : used to store a collection of values of the same data type.
  • objects : used to store instances of classes.

Type Conversion:

There may be cases where it is necessary to convert a variable from one data type to another.

Java provides automatic type conversion for some data types, but for others, explicit type conversion (casting) must be used.

Automatic Type Conversion:

Java automatically converts smaller data types to larger data types.

For example:

int i = 10;
double d = i; // automatic type conversion from int to double

Explicit Type Conversion (Casting):

Explicit type conversion is performed using type casting, which involves specifying the target data type inside parentheses before the value to be converted.

For example:

double d = 10.5;
int i = (int) d; // explicit type conversion from double to int

Final Variables:

Final variables are variables that cannot be reassigned once they have been assigned a value.

They are declared using the final keyword and their value must be assigned at the time of declaration or within a constructor.

The syntax for declaring a final variable is:

final dataType variableName = value;

For example:

final int MAX_AGE = 100;

Scope of Variables:

The scope of a variable determines the part of the program where it can be accessed.

Java has two types of variables: instance variables and local variables.

Instance Variables:

Instance variables are declared within a class, but outside of any method.

They are created when an object of the class is created and destroyed when the object is destroyed.

Instance variables have class-level scope and can be accessed from any method within the class.

Local Variables:

Local variables are declared within a method.

They have method-level scope and can only be accessed within the method in which they are declared.


Variables are an essential aspect of programming in Java. They provide a way to store and manipulate data within a program.

Understanding data types, type conversion, and variable scope is crucial for writing efficient and effective Java code.

By using variables in the appropriate way, you can make your programs more readable, maintainable, and scalable.

Java Basics