Variables are reserved memory locations that can store values based on their data type. There are two main types of variables in Java: primitive and reference. The eight primitive data types are byte, short, int, long, float, double, boolean and char. Each has a specific size and range of values it can hold. Variables must follow naming conventions like being meaningful and avoiding reserved words. Primitive types like int and double are commonly used for numeric values while boolean and char are used for true/false and character values respectively. Reference types represent objects and will be covered separately.

1. Variables & Data Types
Dr. M H B Ariyaratne
https://goo.gl/ytyvLS

2. Variables
● Reserved memory locations to store values
● When we create a variable we reserve some space in
memory.
● Based on the datatype of a variable, the operating
system allocates memory and decides what can be
stored in the reserved memory.
● By assigning different data types to variables, we can
store integers, decimals, or characters in these variables

3. Types of Variables
Primitive Data Types
Reference/Object Data Types

4. Primitive Data Types
Predefined by the language
Named by a keyword
Java - eight primitive data types

5. Naming variables in JAVA
● Variable names are case-sensitive
● An unlimited-length sequence of Unicode letters and digits
● Beginning with a letter, the dollar sign "$", or the underscore character "_"
● White space is not permitted
● Subsequent characters may be letters, digits, dollar signs, or underscore
characters.
● Use full words instead of cryptic abbreviations.
● Must not be a keyword or reserved word.
● If only one word, spell that word in all lowercase letters
● If more than one word, capitalize the first letter of each subsequent word.
● If your variable stores a constant value capitalizing every letter and

6. Primitive Data Types - byte
● Byte data type is an 8-bit signed two's complement
integer
● Minimum value is -128 (-27)
● Maximum value is 127 (inclusive)(27 -1)
● Default value is 0
● Byte data type is used to save space in large arrays,
mainly in place of integers
● Example: byte a = 100 , byte b = -50

7. Primitive Data Types - short
● 16-bit signed two's complement integer.
● Minimum value is -32,768 (-215)
● Maximum value is 32,767 (inclusive) (215 -1)
● Short data type can also be used to save memory as byte
data type. A short is 2 times smaller than an int
● Default value is 0.
● Example: short s = 10000, short r = -20000

8. Primitive Data Type - int
● A 32-bit signed two's complement integer.
● Minimum value is - 2,147,483,648.(-231)
● Maximum value is 2,147,483,647(inclusive).(231 -1)
● int is generally used as the default data type for integral
values unless there is a concern about memory
● The default value is 0.
● Example: int a = 100000, int b = -200000

9. Primitive Data Type - long
● A 64-bit signed two's complement integer.
● Minimum value is -9,223,372,036,854,775,808.(-263)
● Maximum value is 9,223,372,036,854,775,807 (inclusive).
(263 -1)
● This type is used when a wider range than int is needed.
● Default value is 0L.
● Example: long a = 100000L, int b = -200000L

10. Primitive Data Types - float
● A single-precision 32-bit IEEE 754 floating point.
● Float is mainly used to save memory in large arrays of
floating point numbers.
● Default value is 0.0f.
● Example: float f1 = 234.5f

11. Primitive Data Types - double
● A double-precision 64-bit IEEE 754 floating point.
● Generally used as the default data type for decimal
values
● Default value is 0.0d.
● Example: double d1 = 123.4

12. Primitive Data Types - boolean
● Represents one bit of information.
● There are only two possible values: true and false.
● This data type is used for simple flags that track
true/false conditions.
● Default value is false.
● Example: boolean one = true

13. Primitive Data Types - char
● A single 16-bit Unicode character.
● Minimum value is 'u0000' (or 0).
● Maximum value is 'uffff' (or 65,535 inclusive).
● Char data type is used to store any character.
● Example: char letterA ='A'

14. Reference Data Types
We will discuss them under as a separate presentation on Objects and Strings.

15. Thank you