Variables and Data Types

Variables and Data Types

Token

Whenever we are discussing a Java program, it basically deals with the characters (i.e., an alphabet/ a number/ special characters). Each individual character used in the Java program is termed a Token.

  • Token is the fundamental unit of a Java program.

  • It may be compared with the cell in the human body. (As a cell is the fundamental and functional unit of the human body, a token may also be referred to as a cell of the Java program).

  • There are various types of tokens that are available in Java. They are :

  • Keywords

  • Identifiers
  • Operators
  • Literals
  • Separators

In Simple words -> What you type is what you get.

  • Integer Literals - whole numbers having positive or negative values. e.g.: 104, 550, -35, etc.

  • Real Literals - represent numbers with decimal points. e.g.: 26.54, 0.54, -7.658, etc.

  • Character Literals - All alphabets, digits, and special characters can be termed character literals. e.g.: 'A', 'd', '4', '*'.

  • String Literals - It consists of a group of characters inside double quotes. e.g.: "Year2022", "HackForCode", etc.

  • Boolean Literals - It consists of the keywords; true and false. These keywords can be used anywhere you need a test.

Data Types

In Java, we have to deal with various types of data, hence it becomes necessary for a programmer to select an appropriate data type according to the data taken in a program.

Primitive Data Types

  • Primitive data types are built-in data types.
  • Primitive data types are those data types that are not breakable.
  • Java supports 8 types of primitive data types.

Non Primitive Data Types

  • They are basically defined as derived data types.
  • They are directly or indirectly dependent on primitive data types.
  • They are also called the Reference data type.

  • Array

  • String
  • Class
  • Interface

Data-types-in-Java.png


Integar Type

  • A variable declared integer type contains a whole number.
  • They may be a positive or a negative number but without a decimal point.
TypeSizeUse
byte1 byteapplied for a very small value range from -128 to 127
short2 bytesapplied for a small range of value varies between -32768 to 32767
int4 bytesapplied for integers that are more than short integers
long8 bytesapplied for large integers

Note:- 1 byte = 8 bits


Float Types

TypeSizeUsePrecision
float4 bytesIt represents a fractional number with a small ranges7 digits
double8 bytesIt represents a fractional number with wide range values15 digits
  • some valid floating points:
  • 5.0
  • +3.4256, .58
  • some invalid floating points:

  • 1000 (Decimal missing)

    1. (fractional portion is missing)
  • ±20.123 (Both signs are not allowed)
  • 20,23.154 (comma not allowed)
  • 20 23.154 (blank space between digits not allowed & blank space after sign not allowed)
  • Representation in Exponent form in Java

  • 9.136 x 10^8 can be written as 9.136E8

  • 9.136 x 10^-8 can be written as 9.136E-8

Character Types

  • It contains a single character.
  • There are 256 characters available with the computer. These characters are termed as ASCII characters.
  • Each ASCII character is allotted a specific numeric code called ASCII code.
  • The ASCII codes of the characters range from 0 to 255.

ASCII code of the characters is as follows :

  • A - Z : 65 - 90
  • a - z : 97 - 122
  • 0 - 9 : 48 - 57

The character types in Java are as follows :

TypeSizeExample
char2 bytes'A', 'd', '4'
stringmore than 2 bytes"Ad4", "H"

Note:

  • A character is enclosed in single quotes (' ')
  • Strings are enclosed in double quotes (" ")


    Boolean Type

  • It contains a constant as True or False.


    Variables

  • A variable is the name of the location where the value is stored.

  • This location exists in computer memory where the value can be stored and in case of need, it can be retrieved.

Declaration

  • int val;
  • float points;

Assignation

  • val = 12;
  • points = 52.314f

Initialization

M-1: Initialize a variable in two statements

dataType variableName;
variableName = value;

M-2: Initialize in one statement

dataType variableName = value;

Identifiers

  • All java components require names. Names of variables, methods, classes, packages, etc. is known as identifiers.
  • It allows a programmer to refer to the item from other places in the program.

Rules for naming a variable

  • A variable may have any number of characters.
  • It may contain alphabets, digits, and underscore.
  • Variable name should be meaningful and easily depict the logic.

Rules for variable to be invalid

  • Variable names should not start with a digit or special character. (It can start with an underscore)
  • A variable name should not include a space in between its characters.
  • A digit should not be applied in between the characters of a variable name.
  • A variable name should not be a Keyword.

keyword

Java Reserved words are those keywords that cannot be used as variable names in the programs. A list of java reserved keywords has been given below:

key.jpg

true, false, and null are not reserved words but cannot be used as identifiers.(because they are literals of built-in types).


Punctuators

  • Punctuators are the signs used as special characters in Java.
  • some of them are . (dot), ; (semi colon), etc.
  • Dot (.) is used to represent the scope of a function.
  • Semi Colon (;) is used in the java programs as a statement terminator. Any line continued after a semi-colon is treated as the next line.

    Separators

They are the special characters in Java, which are used to separate the variables or the characters. Example :- Comma (,) , Brace ( ) , Culry Braces { } , Square Braces [ ] , etc.


Operators

In the next lecture. Till then keep learning!


Keep Growing!!