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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
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