# 15 Fundamental of Java in Details | Variable | DataType | Java Tutorial in Hindi | Java Basic смотреть онлайн

1.Keywords: - A keyword is a predefined reserved word whose meaning is fixed in the programming language.
Type of keywords in java: -

There are approximately 52+ keywords used in java.
*Java is a Case Sensitive language.
In java all keywords must be written in small letters of Lower Case.
2. Identifiers: - Identifiers are the names of variables, methods, classes, packages, object, label and interfaces.
Rules to declare Identifiers: -
a) It can’t be a keyword.
b) The length of an identifier must be greater than 0 means it can’t be blank.
c) The first character must be picked from: alpha, underscore, or dollar sign. The first character cannot be a digit.
d) Blank Space and dot operator are not allowed.
e) In special characters only ‘_’ Underscore and ‘$’ symbols are allowed.

• Examples of legal identifiers: age, $salary, _value, __1_value.
• Examples of illegal identifiers: 123abc, -salary.
Conventions to Declare Identifiers:
Conventions for class identifiers:-
• If a class identifier contains single word, the 1st letter of the class-name should be in capital letters because the inbuilt classes made by Sun Microsystems have the 1st letter of their class-names in capital.
The main advantage of this convention is that the readability of the program increases.
• If a class identifier contains more than one word, then the 1st letter of each word should be capital letters.
• #Example
public class Employee public class EmployeeDetails
{ {
//code snippet //code snippet
} }
Conventions for interface identifiers:-
• The convention for interface identifiers is same as that of the class identifiers. Should be capital letters.
#Example
interface Printable interface PrintableInter
{ {
//code snippet } //code snippet }
Conventions for method identifiers:-
• If a method identifier contains a single word, then it should be written in lower case.
• If a method identifier contains more than one word, the 1st letter of each word should be capital except the 1st word.
class Employee class Employee
{ {
//method //method
void show() void showDetails()
{ {
//code snippet //code snippet
} }
} }

Conventions for variables identifiers or data members:
• All the variables are written in lower case.
• All private and local variables use only lowercase letters combined with underscores.
• Variables that represent constant values use all uppercase letters and underscores between words.
#Example
public class Employee
{
int id;
String college_name;
float price1;
int _rn;
int $mob;
pubic static final int MAX_AGE;

}

Conventions for package.
All the variables are written in lower case.
#Example
package employeeofsurya; //name of package
public class EmployeeDetails
{
//code snippet
}

Conventions for Constant identifiers:-
• It should be in uppercase letters such as RED, YELLOW.
• If the name contains multiple words, it should be separated by an underscore ‘_’ such as MAX_PRIORITY.
• It may contain digits but not as the first letter.
#Example
class Employee
{
//constant
static final int MIN_AGE = 18;

//code snippet
}

Variable: - A variable is a name given to a memory location. It is the basic unit of storage in a program which refer the value of specific address.
• The value stored in a variable can be changed during program execution.
• A variable is only a name given to a memory location, all the operations done on the variable effects that memory location.
• In Java, all the variables must be declared before use.
• From OOPs point of view in java variables are also known as Data Members (D.M).


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