Language Fundamentals - Variable declarations and Identifiers

Syntax

        modifiers Type declarator;

Example:
        public int i;
        private long myNumber;
        protected myVar = 10;        

• variables provide named access to data stored in memory
• variables may be declared as a primitive type or a reference type
• Java supports two different kinds of variables: field or class variables and local or automatic variables
• field variables are declared as members of a class; they store information (data) relating to an object
• valid field modifiers: public, protected, private, final, static, transient, volatile
• local or automatic variables are declared within methods; they are temporary placeholders which store values and references to data for objects being operated on by the method
• valid local modifiers: final

Identifiers

• an identifier is an unlimited-length sequence of Java letters and Java digits
• an identifier cannot have the same spelling as a Java keyword, boolean literal, or null literal
• valid identifiers begin with one of the following:
  • a Unicode letter
  • the underscore character ( _ )
  • a dollar sign ( $ )
• JLS §3.8 recommends that the dollar sign only be used for identifiers that are mechanically generated (ie within IDE's)
• JPL pg 5.4 recommends sticking to one language when writing identifiers as a number of characters look alike in various languages but have seperate Unicode values
• methods and variables can have the same names; method identifiers always take the form

      methodName()
  

  the parantheses allow Java to recognize the identifier as a method vs a variable and therefore distinguish between the two.

Naming Conventions

• Package names - lowercase.for.all.components
• Class and Interface names - CaptializedWithInternalWordsCaptialized
• Method names - firstWordLowercaseButInternalWordsCapitalized()
• Variable names - firstWordLowercaseButInternalWordsCaptialized
• Constants - UPPER_CASE_WITH_UNDERSCORES

Tips

• variables can have the same name as a method or a class

Traps

• local (automatic) variables declared with a modifier other than final
• identifier names beginning with a number or # sign