Tokens in Java

Java tokens | In Java, tokens are the smallest unit in a program that can’t be divided further. Except for comments and white space, anything we write in the Java program will be treated as a token.

Java supports five different tokens,

1. Identifiers
2. Keywords
3. Literals
4. Operators
5. Special Symbols

Every word or symbol written in the below Java program will come under any one of the above five tokens.

class Test{
   public static void main(String[] args) {
      int number=9;
      double variable=1.5;
      System.out.println(number+variable);
      System.out.println(variable==number);
      System.out.println("Hello");
   }
}

Identifiers

The name of the basic programming element is called Identifier. The identifiers in Java are used for identifying or finding a programming element from other parts of the program or project.

There are certain rules for defining an identifier. If we define any basic programming element without a name then we will get a compile-time error: <identifier> expected.

Keywords

A predefined identifier that has special meaning in a Java program outside comment and string is called a Keyword. Or, A keyword is a reserved word in Java language inside the compiler and JVM that perform a unique and special operation. A word that is created as part of the compiler and JVM software to represent a value is called Reserved words.

In Java, there are 64 reserved words, among them 51 are keywords, 3 are literals and 10 restricted words are there.

Reserved words (64)

• Keywords (51)
• Literals (3)
• Restricted words (10)

Keywords are used to communicate with compiler and JVM to perform one special operation on our program.

Table with all Java keywords

_	extends	protected
abstract	final	public
assert	finally	return
boolean	float	short
break	for	static
byte	goto	strictfp
case	if	super
catch	implements	switch
char	import	synchronized
class	instanceof	this
const	int	throw
continue	interface	throws
default	long	transient
do	native	try
double	new	void
else	package	volatile
enum	private	while

Literals

Any constant value in the program is called a literal. Literals in Java are used to represent value or assign variables value. Examples of literals:- 9, 9.5, ‘a’, “a”, true, false, null, and e.t.c.

Types of literals in Java

Based on the different types of data we store in the program, Java supports 7 types of literals. These are,

• Integral literals
• Floating-point literals
• Character literals
• Conditional literals
• String literals
• Null Literals

Integral, floating-point, and character literals examples,

Data Types	Literals Example
byte	(byte)9, (byte)50 e.t.c.
short	(short)10, (short)50 e.t.c.
int	9, 5, 50, 800 e.t.c.
long	9L, 10L, 55L e.t.c.
float	5.0F, 9.0F, 50.5F, e.t.c
double	5.0, 50.5, 95.2, e.t.c
char	‘A’, ‘a’, ‘5’, ‘@’, ‘$’, e.t.c

Other Literals

Literals	Example
Conditional literals (boolean)	true, false
String literals	“a”, “Hello”, e.t.c.
Null literal	null

Operators

In Java Operators are given to perform various mathematical operations. The different operators in Java are,

• Arithmetic Operators
• Increment and Decrement Operators
• Assignment Operators
• Relational Operators
• Logical Operators
• Ternary Operators
• Bitwise Operators
• Shift Operators
• Instanceof operator

Arithmetic Operators used to perform mathematical operations. The arithmetic operators in Java can operate on any built-in data type. These are,

Operator	Meaning
+	Addition
–	Substraction
*	Multiplacation
/	Division
%	Modulus

Increment and decrement operators in Java are also known as unary operators because they operate on a single operand. The increment operator (++) adds 1 to its operand and decrement operator (–) subtracts one.

Operator	Meaning
++	Increment Operator
_ _	Decrement Operator

Special Symbols

Special Symbols: These symobols having some special meaning in the program. These are total 12 special symbols:- ( ) { } [ ] ; , . ... @ ::

Special Symbols	Used for
()	Generally it is used for method calls and method parameters.
{}	It is used to indicate the start and end of a block of the code containing more than one executable statement.
[]	It is used for array element reference.
;	Used to terminate the statement.
,	Used to seperate two values.
.	It is used to access data of an object.
...	It is used with var args.
@	Used with annonation.
::	Used to call a method by referring to it with the help of its class directly.

Some important points:-

• ::(double colon) is a separator, not an operator in Java. It is used for referencing method and constructor. It was given in the Java1.8 version.
• The arrow(->) is a lambda expression, not a separator in Java, and it was also given in the Java1.8 version.
• The separators ... and @ were given in Java1.5 version.

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Java basic elements

Java supports 10 programming elements for implementing object-oriented programming concepts by using Java language.

1. Module (from Java9 onwards):- used for grouping related packages and their classes.
2. package:- It is a folder used to group related classes, interfaces, and enums. It is also used to separate new classes from existed classes if both have the same name.
3. class:- It is used for declaring real-world objects. An abstract class is used for declaring some operations and implementing some other. A concrete class is used for implementing all operations. The final class is used for implementing all operations and to stop creating subclasses.
4. Interface:- It is used only for declaring object operation.
5. enum (from Java1.5 onwards):- It is meant for declaring named constants.
6. annotation (from Java1.5 onwards):- It is used for providing a description and configurational values.
7. Variable:- it is a named memory location used to store Java data, such as numbers, characters, strings, etc.
8. Method:- It is a sub-block of a class used to implement the logic of object operations. Rule:- Logic should be placed only inside a method, can’t be placed at the class level directly.
9. Constructor:- It is used for initializing the object.
10. Block:- It is also used for initializing an object.

Note:- Constructor and block are allowed only inside a class and enum.

The interface is a fully unimplemented class, it is used for defining set object operations. Whereas class is fully implemented, it is used for implementing object operations.

Enum was introduced in Java 5 version to create a set of named constants for creating menu kind of items such as Restaurant, Bar menu.

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