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Note: Some keywords like const and goto are not in use currently. They are reserved for future use.




              3.4.2 Identifiers
              Identifiers are the names given to different components of a Java program like class, variables and methods. It can
              be a combination of letters and numbers or simply a sequence of letters. Keywords cannot be used as identifiers. An
              identifier must differ in spelling or case from any keyword. After an identifier is declared it can be used later in program
              statements to refer to the associated value.

              Identifier Naming Conventions
              Following are some protocols that are followed while naming the identifiers:
              •  An identifier must start with a letter (a–z or A–Z) or underscore (_) or dollar ($).
              •  An identifier does not start with a digit. However, apart from the first character, it can have any combination of
                 letters or digits.
              •  An identifier is case-sensitive which means "AGE" and "age" are two different identifiers.
              •  An identifier can be of any length.
              •  An identifier cannot contain whitespaces.
              •  An identifier cannot be a Java keyword.
              •  An identifier must not contain any type of special symbol apart from underscore (_) or dollar ($) sign.


              Examples of Valid Identifiers
              According to the protocols of identifiers naming, some of the valid identifiers are:

              Name, $add, _cost, marks_computer, country_91,  etc.

              Examples of Invalid Identifiers
              According to the protocols of identifiers naming, some of the invalid identifiers with reasons are:

                   Invalid                                                               Definition
                  Identifier            Reason for Invalidity
               91country       An identifier cannot start with a number.   Identifiers in Java are a sequence of characters
                                                                           to identify something  in a program.  They are
               cost price      An identifier cannot contain whitespace.    names given to  a class, variable, package,
               s+p             An identifier must not contain any special   method, or interface and allow the programmer
                               symbols apart from $ and _.                 to refer to the specific item from any place in
               class           An identifier cannot use a keyword.         the program.

              3.4.3 Literals
              Literals  are  the  values  that  can  be  stored  in  the  variables.  Unlike  variables,  they  cannot  change  once  assigned.
              So, literals are also called constants. There are six types of literals which are:

              •  Integer Literals                     •   Floating-Point Literals
              •   Character Literals                  •   String Literals
              •   Boolean Literals                    •   The null Literal

              Let us learn about them in detail.

              Integer Literals
              An integer literal is a whole number or the number without a decimal point. It may be a positive or a negative value.
              There are four types of integer literals supported by the Java language which are decimal integer literals, binary integer



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