What are Java Variables and Data Types?

1. What is a Java Variable?

A variable can be called a container that holds some value in a Java program. The variable has assigned a data type that defines what type of value the variable can hold. The variable has a name which locates in the memory. 

If you want to use a variable in a program, there are two steps associated with it you have to perform:

• Variable Declaration
• Variable Initialization

i. Variable Declaration

While declaring a variable you have to assign a data type with the variable name. The variable name has to be unique.

Example: String employee;

ii. Variable Initialization

It means assigning a value to the declared variable.

Example: employee = "John"

The above two steps (declaration and initialization) can also be joined together in one single step.

Example: String employee = "John";

Let's explain the above example, 

• 'String' is a data type
• 'employee' is the name of the variable
• "John" is the value assigned to a variable named employee.

2. Types of Java Variables

Java has three types of variables:

1. Local Variables
2. Instance Variables
3. Static Variables

2.1. Local Variables

A variable that is declared inside a method is a local variable. These variables can only be used within that method as their scope lies only inside that method.

2.2. Instance Variables

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

2.3. Static Variables

A variable that is declared with the keyword 'static' and outside the method is called a static variable. Static variables are allocated memory when a class is loaded in memory. Static variables are initialized before instance variables.

Code example for Java Variable Types:

package com.techlistic.java;

public class JavaVaribales {
 
 // Instance Variables
 int x = 15;
 
 
 // Static Variables
 static String message = "Hello World!";
 
 
 // Main Method
 public static void main(String[] args) {
  
  // Local variables
  int a = 10; 
  int b = 20;
  
  // Some code here
  // ---------
  // ---------
 }
 
 
 // Method
 void myMethod() {

  // Local Variables
  char ch = 'i';
  float num = (float) 1.5;

 }

}

3. Java Data Types

As we already discussed in the previous tutorial every Java variable has a data type. Data type tells us the different sizes and values that can be stored in a variable.

Java has two Data Types:

1. Primitive Data Types
2. Non-Primitive Data Types

3.1. Primitive Data Types

Primitive data types are built-in within Java language. No additional methods are required for it. There are 8 primitive data types:

1. byte
2. short
3. int
4. long
5. float
6. double
7. boolean
8. char

Data Type	Default Value	Default size
byte	0	1 byte
short	0	2 bytes
int	0	4 bytes
long	0L	8 bytes
float	0.0f	4 bytes
double	0.0d	8 bytes
boolean	false	1 bit
char	'\u0000'	2 bytes

1. byte : 

Its value range lies between -128 to 127. Byte is used in place of int to save memory as a byte is 4 times smaller than an integer. Its default value is 0.

Example: 

byte x = 10;

byte y = 20;

2. short : 

The range of short data type lies between -32,768 to 32,767. The short data type can again be used to save memory instead of int. Short is 2 times smaller than int. Its default value is 0.

Example:

short s = 12000;

short t = -10000;

3. int : 

int is also known as an integer. Its range value lies between -2,147,483,648 to 2,147,483,647. Its default value is 0. This is the most commonly used data type for integral values.

Example:

int x = 10;

int y = 2000;

4. long : 

The long data type is 8 bytes. Its value range lies between -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. long data type is used when a large range of values is required which are not provided by int. Its default value is 0.

Example:

long l = 100000L;

long m = -300000L;

5. float :

The float data type is used for decimal values. Its range is unlimited. float is recommended over double data type to save memory. Its default value is 0.0F.

Example:

float f = 20.5f;

6. double :

double data type is generally used for decimal values just like float. Its range is unlimited. Its default value is 0.0d.

Example:

double d = 10.5;

7. boolean :

The boolean data type can only store one of the two values: true or false.

Example:

boolean flag = false;

boolean isJavaInteresting = true;

8. char :

The char data type is used to store characters. The character must be within single quotes ('a').

Example:

char grade = 'A';

3.2. Non-Primitive Data Types

Non-Primitive data types are not defined by Java and are created by programmers except Strings. Unlike primitive, non-primitive data types can be null. Non-Primitive data types are:

1. Strings
2. Arrays
3. Classes
4. Interface etc.

i. Strings :

The String data type is used to store the sequence of characters or text. Strings must be declared within double quotes like "Hello".

Example:

String myName = "John"; 

Also, read - Java Tutorials Series

Next >>  Java Modifiers

Author

Vaneesh Behl

Passionately writing and working in Tech Space for more than a decade.