This document provides an overview of tokens, keywords, identifiers, and examples of valid and invalid identifiers in Java. It discusses that tokens are the smallest elements of a program and describes the different types of tokens as keywords, identifiers, literals, operators, and separators. Keywords are predefined reserved words that cannot be used as variable, class, or method names. Identifiers are symbolic names used to identify classes, variables, functions, objects, and data members. The document outlines rules for identifiers and provides examples of valid identifiers that follow the rules as well as invalid identifiers that violate the rules.

1. BLUE J
CHP- 3
VALUE & DATA TYPES
LECTURE 1
PRESENTED BY MD ARBAZ KHAN

2. ENGLISH
Character
Word
sentences
Paragraph
Code/language
Java
Character
Tokens
Statement
Method/function
Code/language
Value & Data Types

3. TOKENS
A token is the smallest elements of a program.
The different types of token in java are :-
1. Keyword
2. Indentifiers
3. Literals
4. Operators
5. Seperators

4. KEYWORDS
• Keywords is also known as Reserved words. These are predefined words by Java so they
cannot be used as a variable or object name or class name.
• Ex- int
for
Double
If
else
class

5. IDENTIFIERS
Identifiers in Java are symbolic names used for identification. They can be a class name, variable
name, method name, package name, constant name.
Rules:-
1. Indentifiers is the name assigned to an elements in a program
Examples: classes, variables, function, object & data member.
I. Identifiers may contain an alphabets, digit and two special symbols ($) & (_).
II. The first character of an indentifiers can only contain alphabet (a-z) (a-z).
III. No blanks spaces b/w the indentifiers.
IV. An identifier should not contain a number at the starting

6. SIMPLE JAVA PROGRAM
1.HelloJava (Class name)
2.main (main method)
3.String (Predefined Class name)
4.args (String variables)
5.System (Predefined class)
6.out (Variable name)
7.println (method)

7. EXAMPLES OF INVALID INDENTIFIER
Invalid identifiers:
Below are some examples of invalid identifiers:
•Test Variable ( We can not include a space in an identifier)
•123javatpoint ( The identifier should not begin with numbers)
•java+tpoint ( The plus (+) symbol cannot be used)
•a-javatpoint ( Hyphen symbol is not allowed)
•java_&_Tpoint ( ampersand symbol is not allowed)
•Java'tpoint (we can not use an apostrophe symbol in an identifier)

8. CASE 1-
SPACE IN WORDS
CASE 2-
FIRST LETTER IS NUMBER
CASE 3-
FIRST LETTER IS NOT A
DOLLAR OR UNDERSCORE

9. EXAMPLES OF VALID IDENTIFIER IN JAVA:
•TestVariable
•testvariable
•a
•i
•Test_Variable
•_testvariable
•$testvariable
•sum_of_array
•TESTVARIABLE
•jtp123
•JavaTpoint
•Javatpoint123

10. CASE 1- USE OF WORDS,
UNDERSCORE & NUMBER
CASE 2- NO SPACE B/W
DOLLAR AND WORD
CASE 3- WORDS WITHOUT
SPCE

11. TO BE CONTINUE….