Introduction to Variables and Primitive Data Types

A variable is a named memory location that can be assigned a value while the program is running. A data type describes the sort of data that a variable will hold. This tutorial will introduce you to one of the fundamental Java data types - the primitive data types.

The following is a list of all eight of the primitive data types. This tutorial will focus on just the int and double data types.

  • byte · 8-bit integer, -128 to 127
  • short · short integer, -32,768 to 32,767
  • int · integer, -2147483648 to 2147483647
  • long · long integer, -9223372036854775808 to 9223372036854775807
  • float · single-precision floating point
  • double · double-precision floating point
  • boolean · true or false
  • char · unsigned Unicode character

Open the command prompt (CMD - see the Getting Started ) and type in the following commands.

C:\Windows\System32>cd \
C:\>md Java
C:\>cd Java
C:\Java>md Variables
C:\Java>cd Variables

Copy and Paste, or type the following code into Notepad and be sure to save the file when you are done.

    Simple program to convert miles to kilometers
    We create a variable called miles and assign it an int data type and initialize it to 0.
    We create another variable called kilometers and assign it a double data type and initialize it to 0.

class Variables {
    public static void main(String args[]) {
        int miles = 0; // (data type int) (variable miles) (assignment operator =) (value 0) (semicolon)
        double kilometers = 0.0d; // (data type double) (variable kilometers) (assignment operator =) (value 0.0) (semicolon)
        double distance; // (data type double) (variable distance) default value is 0.0d;

        miles = 11; // change the value of the miles variable 
        kilometers = 1.609344d; // change the value of the kilometers variable
        distance = miles * kilometers; // multiply variable values using the multiplication operator (*) and store the value to the distance variable

        System.out.println("There are " + distance + " kilometers in " + miles +" miles." );


Now switch back to the command prompt (CMD) and type in javac and press Enter.
Now type in java Variables and press Enter.

C:\Java\Variables>java Variables
There are 17.702784 kilometers in 11 miles.

Final thoughts

Data types define what type of data a variable can contain. The = assignment operator will store a value to the variable. Java supports arithmetic operators such as +,-,*,/ and more. The int data type has a default value of 0. The double data type has a default value of 0.0d;