Valid characters in a Java class name

Question

What characters are valid in a Java class name  What other rules govern Java class names  for instance  Java class names cannot begin with a number

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Identifiers are used for class names  method names  and variable names  An identifiermay be any descriptive sequence of uppercase and lowercase letters  numbers  or theunderscore and dollar-sign characters  They must not begin with a number  lest they beconfused with a numeric literal  Again  Java is case-sensitive  so VALUE is a differentidentifier than Value  Some examples of valid identifiers are   AvgTemp  count a4   test  this is ok  Invalid variable names include   2count  high-temp  Not ok

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What other rules govern Java class names  for instance  Java class names cannot begin with a number      Java class names usually begin with a capital letter  Java class names cannot begin with a number  if there are multiple words in the class name like  MyClassName  each word should begin with a capital letter  eg-  MyClassName  This naming convention is based on CamelCase Type

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Every programming language has its own set of rules and conventions for the kinds of names that you re allowed to use  and the Java programming language is no different  The rules and conventions for naming your variables can be summarized as follows          Variable names are case-sensitive  A variable s name can be any legal identifier     an unlimited-length sequence of Unicode letters and digits  beginning with a letter  the dollar sign      or the underscore character      The convention  however  is to always begin your variable names with a letter  not     or      Additionally  the dollar sign character  by convention  is never used at all  You may find some situations where auto-generated names will contain the dollar sign  but your variable names should always avoid using it  A similar convention exists for the underscore character  while it s technically legal to begin your variable s name with      this practice is discouraged  White space is not permitted    Subsequent characters may be letters  digits  dollar signs  or underscore characters  Conventions  and common sense  apply to this rule as well  When choosing a name for your variables  use full words instead of cryptic abbreviations  Doing so will make your code easier to read and understand  In many cases it will also make your code self-documenting  fields named cadence  speed  and gear  for example  are much more intuitive than abbreviated versions  such as s  c  and g  Also keep in mind that the name you choose must not be a keyword or reserved word    If the name you choose consists of only one word  spell that word in all lowercase letters  If it consists of more than one word  capitalize the first letter of each subsequent word  The names gearRatio and currentGear are prime examples of this convention  If your variable stores a constant value  such as static final int NUM GEARS   6  the convention changes slightly  capitalizing every letter and separating subsequent words with the underscore character  By convention  the underscore character is never used elsewhere        From the official Java Tutorial

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You can have almost any character  including most Unicode characters   The exact definition is in the Java Language Specification under section 3 8  Identifiers   An identifier is an unlimited-length sequence of Java letters and Java digits  the first of which must be a Java letter      Letters and digits may be drawn from the entire Unicode character set      This allows programmers to use identifiers in their programs that are written in their native languages  An identifier cannot have the same spelling  Unicode character sequence  as a keyword    3 9   boolean literal    3 10 3   or the null literal    3 10 7   or a compile-time error occurs   However  see this question for whether or not you should do that

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I d like to add to bosnic s answer that any valid currency character is legal for an identifier in Java   th   is is a legal identifier  as is    this  and     as well   However  I can t figure out how to edit his or her answer  so I am forced to post this trivial addition

User · Answer

Every programming language has its own set of rules and conventions for the kinds of names that you re allowed to use  and the Java programming language is no different  The rules and conventions for naming your variables can be summarized as follows          Variable names are case-sensitive  A variable s name can be any legal identifier     an unlimited-length sequence of Unicode letters and digits  beginning with a letter  the dollar sign      or the underscore character      The convention  however  is to always begin your variable names with a letter  not     or      Additionally  the dollar sign character  by convention  is never used at all  You may find some situations where auto-generated names will contain the dollar sign  but your variable names should always avoid using it  A similar convention exists for the underscore character  while it s technically legal to begin your variable s name with      this practice is discouraged  White space is not permitted    Subsequent characters may be letters  digits  dollar signs  or underscore characters  Conventions  and common sense  apply to this rule as well  When choosing a name for your variables  use full words instead of cryptic abbreviations  Doing so will make your code easier to read and understand  In many cases it will also make your code self-documenting  fields named cadence  speed  and gear  for example  are much more intuitive than abbreviated versions  such as s  c  and g  Also keep in mind that the name you choose must not be a keyword or reserved word    If the name you choose consists of only one word  spell that word in all lowercase letters  If it consists of more than one word  capitalize the first letter of each subsequent word  The names gearRatio and currentGear are prime examples of this convention  If your variable stores a constant value  such as static final int NUM GEARS   6  the convention changes slightly  capitalizing every letter and separating subsequent words with the underscore character  By convention  the underscore character is never used elsewhere        From the official Java Tutorial

User · Answer

You can have almost any character  including most Unicode characters   The exact definition is in the Java Language Specification under section 3 8  Identifiers   An identifier is an unlimited-length sequence of Java letters and Java digits  the first of which must be a Java letter      Letters and digits may be drawn from the entire Unicode character set      This allows programmers to use identifiers in their programs that are written in their native languages  An identifier cannot have the same spelling  Unicode character sequence  as a keyword    3 9   boolean literal    3 10 3   or the null literal    3 10 7   or a compile-time error occurs   However  see this question for whether or not you should do that

User · Answer

You can have almost any character  including most Unicode characters   The exact definition is in the Java Language Specification under section 3 8  Identifiers   An identifier is an unlimited-length sequence of Java letters and Java digits  the first of which must be a Java letter      Letters and digits may be drawn from the entire Unicode character set      This allows programmers to use identifiers in their programs that are written in their native languages  An identifier cannot have the same spelling  Unicode character sequence  as a keyword    3 9   boolean literal    3 10 3   or the null literal    3 10 7   or a compile-time error occurs   However  see this question for whether or not you should do that

User · Answer

Class names should be nouns in UpperCamelCase  with the first letter of every word capitalised  Use whole words     avoid acronyms and abbreviations  unless the abbreviation is much more widely used than the long form  such as URL or HTML   The naming conventions can be read over here   http   www oracle com technetwork java codeconventions-135099 html

User · Answer

As already stated by Jason Cohen  the Java Language Specification defines what a legal identifier is in section 3 8    An identifier is an unlimited-length sequence of Java letters and Java digits  the first of which must be a Java letter        A  Java letter  is a character for which the method Character isJavaIdentifierStart int  returns true  A  Java letter-or-digit  is a character for which the method Character isJavaIdentifierPart int  returns true    This hopefully answers your second question  Regarding your first question  I ve been taught both by teachers and  as far as I can remember  Java compilers that a Java class name should be an identifier that begins with a capital letter A-Z  but I can t find any reliable source on this  When trying it out with OpenJDK there are no warnings when beginning class names with lower-case letters or even a  -sign  When using a  -sign  you do have to escape it if you compile from a bash shell  however

User · Answer

What other rules govern Java class names  for instance  Java class names cannot begin with a number      Java class names usually begin with a capital letter  Java class names cannot begin with a number  if there are multiple words in the class name like  MyClassName  each word should begin with a capital letter  eg-  MyClassName  This naming convention is based on CamelCase Type

User · Answer

Every programming language has its own set of rules and conventions for the kinds of names that you re allowed to use  and the Java programming language is no different  The rules and conventions for naming your variables can be summarized as follows          Variable names are case-sensitive  A variable s name can be any legal identifier     an unlimited-length sequence of Unicode letters and digits  beginning with a letter  the dollar sign      or the underscore character      The convention  however  is to always begin your variable names with a letter  not     or      Additionally  the dollar sign character  by convention  is never used at all  You may find some situations where auto-generated names will contain the dollar sign  but your variable names should always avoid using it  A similar convention exists for the underscore character  while it s technically legal to begin your variable s name with      this practice is discouraged  White space is not permitted    Subsequent characters may be letters  digits  dollar signs  or underscore characters  Conventions  and common sense  apply to this rule as well  When choosing a name for your variables  use full words instead of cryptic abbreviations  Doing so will make your code easier to read and understand  In many cases it will also make your code self-documenting  fields named cadence  speed  and gear  for example  are much more intuitive than abbreviated versions  such as s  c  and g  Also keep in mind that the name you choose must not be a keyword or reserved word    If the name you choose consists of only one word  spell that word in all lowercase letters  If it consists of more than one word  capitalize the first letter of each subsequent word  The names gearRatio and currentGear are prime examples of this convention  If your variable stores a constant value  such as static final int NUM GEARS   6  the convention changes slightly  capitalizing every letter and separating subsequent words with the underscore character  By convention  the underscore character is never used elsewhere        From the official Java Tutorial

User · Answer

I d like to add to bosnic s answer that any valid currency character is legal for an identifier in Java   th   is is a legal identifier  as is    this  and     as well   However  I can t figure out how to edit his or her answer  so I am forced to post this trivial addition

User · Answer

Every programming language has its own set of rules and conventions for the kinds of names that you re allowed to use  and the Java programming language is no different  The rules and conventions for naming your variables can be summarized as follows          Variable names are case-sensitive  A variable s name can be any legal identifier     an unlimited-length sequence of Unicode letters and digits  beginning with a letter  the dollar sign      or the underscore character      The convention  however  is to always begin your variable names with a letter  not     or      Additionally  the dollar sign character  by convention  is never used at all  You may find some situations where auto-generated names will contain the dollar sign  but your variable names should always avoid using it  A similar convention exists for the underscore character  while it s technically legal to begin your variable s name with      this practice is discouraged  White space is not permitted    Subsequent characters may be letters  digits  dollar signs  or underscore characters  Conventions  and common sense  apply to this rule as well  When choosing a name for your variables  use full words instead of cryptic abbreviations  Doing so will make your code easier to read and understand  In many cases it will also make your code self-documenting  fields named cadence  speed  and gear  for example  are much more intuitive than abbreviated versions  such as s  c  and g  Also keep in mind that the name you choose must not be a keyword or reserved word    If the name you choose consists of only one word  spell that word in all lowercase letters  If it consists of more than one word  capitalize the first letter of each subsequent word  The names gearRatio and currentGear are prime examples of this convention  If your variable stores a constant value  such as static final int NUM GEARS   6  the convention changes slightly  capitalizing every letter and separating subsequent words with the underscore character  By convention  the underscore character is never used elsewhere        From the official Java Tutorial

User · Answer

You can have almost any character  including most Unicode characters   The exact definition is in the Java Language Specification under section 3 8  Identifiers   An identifier is an unlimited-length sequence of Java letters and Java digits  the first of which must be a Java letter      Letters and digits may be drawn from the entire Unicode character set      This allows programmers to use identifiers in their programs that are written in their native languages  An identifier cannot have the same spelling  Unicode character sequence  as a keyword    3 9   boolean literal    3 10 3   or the null literal    3 10 7   or a compile-time error occurs   However  see this question for whether or not you should do that

User · Answer

Further to previous answers its worth noting that    Java allows any Unicode currency symbol in symbol names  so the following will all work        var1     var2      var3   I believe the usage of currency symbols originates in C C    where variables added to your code by the compiler conventionally started with      An obvious example in Java is the names of   class  files for inner classes  which by convention have the format  Outer Inner class    Many C  and C   programmers adopt the convention of placing  I  in front of interfaces  aka pure virtual classes in C     This is not required  and hence not done  in Java because the implements keyword makes it very clear when something is an interface    Compare      class Employee   public IPayable   C     with     class Employee   IPayable   C    and      class Employee implements Payable   Java    Many projects use the convention of placing an underscore in front of field names  so that they can readily be distinguished from local variables and parameters e g       private double  salary    A tiny minority place the underscore after the field name e g      private double salary

User · Answer

As already stated by Jason Cohen  the Java Language Specification defines what a legal identifier is in section 3 8    An identifier is an unlimited-length sequence of Java letters and Java digits  the first of which must be a Java letter        A  Java letter  is a character for which the method Character isJavaIdentifierStart int  returns true  A  Java letter-or-digit  is a character for which the method Character isJavaIdentifierPart int  returns true    This hopefully answers your second question  Regarding your first question  I ve been taught both by teachers and  as far as I can remember  Java compilers that a Java class name should be an identifier that begins with a capital letter A-Z  but I can t find any reliable source on this  When trying it out with OpenJDK there are no warnings when beginning class names with lower-case letters or even a  -sign  When using a  -sign  you do have to escape it if you compile from a bash shell  however

User · Answer

I d like to add to bosnic s answer that any valid currency character is legal for an identifier in Java   th   is is a legal identifier  as is    this  and     as well   However  I can t figure out how to edit his or her answer  so I am forced to post this trivial addition

User · Answer

Class names should be nouns in UpperCamelCase  with the first letter of every word capitalised  Use whole words     avoid acronyms and abbreviations  unless the abbreviation is much more widely used than the long form  such as URL or HTML   The naming conventions can be read over here   http   www oracle com technetwork java codeconventions-135099 html

User · Answer

I d like to add to bosnic s answer that any valid currency character is legal for an identifier in Java   th   is is a legal identifier  as is    this  and     as well   However  I can t figure out how to edit his or her answer  so I am forced to post this trivial addition

User · Answer

Further to previous answers its worth noting that    Java allows any Unicode currency symbol in symbol names  so the following will all work        var1     var2      var3   I believe the usage of currency symbols originates in C C    where variables added to your code by the compiler conventionally started with      An obvious example in Java is the names of   class  files for inner classes  which by convention have the format  Outer Inner class    Many C  and C   programmers adopt the convention of placing  I  in front of interfaces  aka pure virtual classes in C     This is not required  and hence not done  in Java because the implements keyword makes it very clear when something is an interface    Compare      class Employee   public IPayable   C     with     class Employee   IPayable   C    and      class Employee implements Payable   Java    Many projects use the convention of placing an underscore in front of field names  so that they can readily be distinguished from local variables and parameters e g       private double  salary    A tiny minority place the underscore after the field name e g      private double salary

User · Answer

Identifiers are used for class names  method names  and variable names  An identifiermay be any descriptive sequence of uppercase and lowercase letters  numbers  or theunderscore and dollar-sign characters  They must not begin with a number  lest they beconfused with a numeric literal  Again  Java is case-sensitive  so VALUE is a differentidentifier than Value  Some examples of valid identifiers are   AvgTemp  count a4   test  this is ok  Invalid variable names include   2count  high-temp  Not ok

User · Answer

Further to previous answers its worth noting that    Java allows any Unicode currency symbol in symbol names  so the following will all work        var1     var2      var3   I believe the usage of currency symbols originates in C C    where variables added to your code by the compiler conventionally started with      An obvious example in Java is the names of   class  files for inner classes  which by convention have the format  Outer Inner class    Many C  and C   programmers adopt the convention of placing  I  in front of interfaces  aka pure virtual classes in C     This is not required  and hence not done  in Java because the implements keyword makes it very clear when something is an interface    Compare      class Employee   public IPayable   C     with     class Employee   IPayable   C    and      class Employee implements Payable   Java    Many projects use the convention of placing an underscore in front of field names  so that they can readily be distinguished from local variables and parameters e g       private double  salary    A tiny minority place the underscore after the field name e g      private double salary

User · Answer

Further to previous answers its worth noting that    Java allows any Unicode currency symbol in symbol names  so the following will all work        var1     var2      var3   I believe the usage of currency symbols originates in C C    where variables added to your code by the compiler conventionally started with      An obvious example in Java is the names of   class  files for inner classes  which by convention have the format  Outer Inner class    Many C  and C   programmers adopt the convention of placing  I  in front of interfaces  aka pure virtual classes in C     This is not required  and hence not done  in Java because the implements keyword makes it very clear when something is an interface    Compare      class Employee   public IPayable   C     with     class Employee   IPayable   C    and      class Employee implements Payable   Java    Many projects use the convention of placing an underscore in front of field names  so that they can readily be distinguished from local variables and parameters e g       private double  salary    A tiny minority place the underscore after the field name e g      private double salary

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