Java Variables

In this tutorial, we will learn about Java variables with the help of examples.

A variable is a container that holds the value while the Java program is executed. A variable is assigned with a data type.

Variable is a name of memory location. There are three types of variables in java: local, instance, and static.

There are two types of data types in Java: primitive and non-primitive.

Variable

Variable is name of reserved area allocated in memory. In other words, it is a name of memory location. It is a combination of “vary + able” that means its value can be changed.

How to declare a variable

data_type variable_name = value;

Rules for Naming Variables in Java

Java programming language has its own set of rules and conventions for naming variables. Here’s what you need to know:

Java is case-sensitive. Hence, keyno and KEYNO are two different variables. For example,

int keyno = 24;
int KEYNO = 25;

System.out.println(keyno);  // prints 24
System.out.println(KEYNO);  // prints 25

Variables must start with either a letter or an underscore, _ or a dollar, $ sign. For example,

int keyno;  // valid name and good practice
int _keyno;  // valid but bad practice
int $keyno;  // valid but bad practice

Variable names cannot start with numbers. For example,

int 1keyno;  // invalid variables

Variable names can’t use whitespace. For example,

int key no;  // invalid variables

Types of Variables

There are three types of variables in Java:

• local variable
• instance variable
• static variable

1) Local Variable

A variable declared inside the body of the method is called local variable. You can use this variable only within that method and the other methods in the class aren’t even aware that the variable exists.

A local variable cannot be defined with “static” keyword.

2) Instance Variable

A variable declared inside the class but outside the body of the method, is called instance variable. It is not declared as static.

It is called instance variable because its value is instance-specific and is not shared among instances.

3) Static variable

A variable which is declared as static is called static variable. It cannot be local. You can create a single copy of static variable and share among all the instances of the class. Memory allocation for static variable happens only once when the class is loaded in the memory.