Java Tokens

In Java, Tokens are the smallest elements of a program that is meaningful to the compiler. They are also known as the fundamental building blocks of the program. Tokens can be classified as follows:

1. Keywords
2. Identifiers
3. Constants/Literals
4. Operators
5. Separators

1. Keyword

Keywords are pre-defined or reserved words in a programming language. Each keyword is meant to perform a specific function in a program. Since keywords are referred names for a compiler, they can’t be used as variable names because by doing so, we are trying to assign a new meaning to the keyword which is not allowed. Java language supports the following keywords:

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

2. Identifiers

Identifiers are used as the general terminology for naming of variables, functions and arrays. These are user-defined names consisting of an arbitrarily long sequence of letters and digits with either a letter or the underscore (_) as a first character. Identifier names must differ in spelling and case from any keywords. You cannot use keywords as identifiers; they are reserved for special use. Once declared, you can use the identifier in later program statements to refer to the associated value. A special kind of identifier, called a statement label, can be used in goto statements. Examples of valid identifiers:

MyVariable
MYVARIABLE
myvariable
x
i
x1
i1
_myvariable
$myvariable
sum_of_array
geeks123

Examples of invalid identifiers:

My Variable  // contains a space
123geeks   // Begins with a digit
a+c // plus sign is not an alphanumeric character
variable-2 // hyphen is not an alphanumeric character
sum_&_difference // ampersand is not an alphanumeric character

3. Constants/Literals 

Constants are also like normal variables. But the only difference is, their values cannot be modified by the program once they are defined. Constants refer to fixed values. They are also called as literals. Constants may belong to any of the data type. Syntax:

final data_type variable_name;

import java.io.*;

class GFG {
    public static void main (String[] args) {
      
        // Here final keyword is used 
        // to define the constant PI
        final double PI = 3.14; // Use double instead of int

        // Example usage of PI
        System.out.println("The value of PI is: " + PI);
    }
}

The value of PI is: 3.14

4. Operators

Java provides many types of operators which can be used according to the need. They are classified based on the functionality they provide. Some of the types are-

• Arithmetic Operators
• Unary Operators
• Assignment Operator
• Relational Operators
• Logical Operators
• Ternary Operator
• Bitwise Operators
• Shift Operators
• instance of operator
• Precedence and Associativity

5. Separators

Separators are used to separate different parts of the codes. It tells the compiler about completion of a statement in the program. The most commonly and frequently used separator in java is semicolon (;).

int variable;   //here the semicolon (;) ends the declaration of the variable

import java.io.*;

class GFG {
    public static void main (String[] args) {
      
        //Here the semicolon (;) used to 
        // end the print statement
        System.out.println("GFG!");  
    }
}

GFG!