Java Keywords and Identifiers, Java Language Fundamentals, Java Programming Syntax, Writing Java Statements and writing Java Code blocks.
Keywords and Identifiers in Java
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.
int myNum = 100;
In the above Java statement, myNum is an identifier (User-defined), it is for identifying the variable.
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.
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 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 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.
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.
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
Note: true, false, null are Java reserved words but not keywords, they are literals.
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