Identifiers in Java

Identifier:

•   In java identifier defined as either class name or interface name or package name or method name or variable name or block name.

•   An identifier is a sequence of one or more characters. The first character must be a valid first character (letter, $, _).
• It allows a programmer to refer to the item from other places in the program.

Example:

package in.blogspot.java2bigdata;
class Identifier1{
int identifier2 =10;
static{
System.out.println("inside static block");
}
public void identifier3(){
}
}

In the above example class name as Idnetifier1,variable name as identifer2, package name as in.blogspot.java2bigdata and method name as identifier3() are considered as Identifiers.


Rules for defining Identifiers in Java:

1.  Allowed char's 0 to 9,a to z,A to Z,underscore( _ ) and dollar ( $ )
     if we are using any other character we will get Compile time error.

2.Identifier should not start with digits.
       int  12number;  // compile time error
       int  number;    // valid identifier

3.Identifier should not a keyword/reserved word (like int,float,public).

4.There is a big difference between case
         int Num;
         int num;
         int NUM;
 above three identifiers are identical.
5.we can use java predefined class names as identifiers but not recommended.
    int System = 10;

6.There is no length limit for java Identifier but not recommend to take more then 15.
   int noLengthLimittttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt;

Legal identifiers examples:

String _t;

String _$;

String _2;

String _____2_u;

String $s;

String this_is_a_long_sample_of_identifier_name;

String ALL_UPPERCASE;

String all_lowercase;

Illegal identifiers examples:

String :c;

String -b;

String s#;

String .d;

String 9n;

String ?what;

String boo+!coo;


Here are some hints on how to formulate identifier name:

    Classes & Interface - The first letter should be capitalized. If the desired name is composed of several words, the first letter of the inner word should be capitalized (camelCase).

    For example: Chair, InformationDepartment and HeadOffice.

    Methods - The first letter should be lower case, and then Lower camelCase rules should be applied. Also, take note that in method names should be verb-noun pairs.

    For example: getTotal, setContactNumber and buyCellphone.
   
    Variables - same rules apply on letter case with methods. However, it should idially be a short and meaningful.
    For example: firstName, currentLocation and totalPrice.
   
    Constants - Java constants should be named using uppercase letters with underscore characters as separator. Take note that constants are created by marking variables as static and final.
    For example: PERSON_LABEL, HELLO_MESSAGE and GREETING.

    CamelCase - CamelCase (also known as Upper CamelCase) is where each new word begins with a capital letter (e.g., CamelCase, CustomerAccount, PlayingCard).

   

mixedCase - Mixed case (also known as Lower CamelCase) is the same as CamelCase except the first letter of the name is in lowercase (e.g., hasChildren, customerFirstName, customerLastName).

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