Java Keywords and Identifiers, Java Language Fundamentals, Java Programming Syntax, Writing Java Statements and writing Java Code blocks.
Keywords and Identifiers in Java
Introduction:
Java keywords are also known as reserved words. Keywords are particular words that act as a key to a code. These are predefined words by Java so they cannot be used as identifiers.
Identifiers in Java are symbolic names used for identification. They can be a class name, variable name, method name, package name, constant name, and more.
Note: Java keywords or reserved words can not be used as an identifier.
Example:
int myNum = 100;
In the above Java statement, myNum is an identifier (User-defined), it is for identifying the variable.
String country=”India”;
In the above Java statement, country is an identifier (User-defined), it is for identifying the variable.
Java statements or steps or instructions are written using keywords, identifiers, data, and special characters.
Example:
int num =100;
In the above statement,
int is Data Type (Java keyword),
num is Identifier (variable vame),
= is assignment operator (special character) and ; (semicolon) is also a special character.
100 is data or value.
Java Keywords:
Java keywords or reserved words are particular words that act as a key to a code. We have “keywords” in every programming language, Java keywords are small letters, and Java is a case-sensitive language.
Java Primitive Data Types:
Java Primitive Data types are keywords, but Non-primitive data types are not keywords
byte – A data type that can store whole numbers from -128 and 127
short – A data type that can store whole numbers from -32768 to 32767
int – A data type that can store whole numbers from -2147483648 to 2147483647
long – A data type that can store whole numbers from -9223372036854775808 to 9223372036854775808
float – A data type that can store whole numbers from 1.7e−308 to 1.7e+308.
double – A data type that can store whole numbers from 1.7e−308 to 1.7e+308.
char – A data type that is used to store a single character.
boolean – A data type that can only store true and false values.
Java Modifiers:
Java access and non-access modifiers are keywords
public – An access modifier used for classes, attributes, methods, and constructors, making them accessible by any other class.
protected – An access modifier used for attributes, methods, and constructors, making them accessible in the same package and subclasses.
private – An access modifier used for attributes, methods, and constructors, making them only accessible within the declared class.
static – A non-access modifier used for methods and attributes. Static methods/attributes can be accessed without creating an object of a class
final – A non-access modifier used for classes, attributes and methods, which makes them non-changeable (impossible to inherit or override)
abstract – A non-access modifier. Used for creating incomplete classes and methods.
etc,
Java Control Flow:
Java control flow (conditional/decision making, looping, and branching) statements are keywords.
if – Makes a conditional statement
else – Used in conditional statements
switch – Selects one of many code blocks to be executed
for – Creates a for loop
do – Used together with while to create a do-while loop.
while – Creates a while loop
break – Breaks out of a loop or a switch block
continue – Continues to the next iteration of a loop
return – Finished the execution of a method, and can be used to return a value from a method.
Others:
class – Defines a class
package – Declares a package
import – Used to import a package, class or interface
new – Creates new objects
try – Creates a try…catch statement
catch – Catches exceptions generated by try statements
etc,
Note: true, false, null are Java reserved words but not keywords, they are literals.
Java Identifiers
In any programming language, identifiers are used for identification purposes. In Java, an identifier can be a class name, method name, variable name, or label. For example :
public class Sample
{
public static void main(String[] args)
{
int num = 1000;
}
}
In the above java code, we have 5 identifiers namely :
Sample: Class name.
main: method name.
String: Predefined class name.
args: Variable name.
num: Variable name.
Rules for defining Java Identifiers
• There are certain rules for defining a valid java identifier. These rules must be followed, otherwise, we get a compile-time error.
• The only allowed characters for identifiers are all alphanumeric characters([A-Z],[a-z],[0-9]), ‘$‘(dollar sign) and ‘_’ (underscore).
• Identifiers should not start with digits([0-9]). For example “7myvaraible” is not a valid Java identifier.
• Java identifiers are case-sensitive.
• There is no limit on the length of the identifier.
• Reserved Words can’t be used as an identifier. For example “int while = 123;” is an invalid statement as while is a reserved word
