Identifier:
A name in java program is called identifier. It may be class name, method name, variable name and label name.
Example:class Test {
public static void main(String args[]){
int a = 20;
}
}
Here Test, main, String[], args, a are identifiers.
Rules to define java identifiers:Rule 1: The only allowed characters in java identifiers are:
1) a to z
2) A to Z
3) 0 to 9
4) _
5) $
Rule 2: If we are using any other character we will get compile time error.
Example:
1) total_number-------valid
2) Total#------------------invalid
Rule 3: identifiers are not allowed to starts with digit.
Example:
1) ABC123---------valid
2) 123ABC---------invalid
Rule 4: java identifiers are case sensitive up course java language itself treated as case sensitive
language.
Rule 5: There is no length limit for java identifiers but it is not recommended to take more than
15 lengths.
Rule 6: We can’t use reserved words as identifiers.
Example: int if=10; --------------invalid
Rule 7: All predefined java class names and interface names we use as identifiers.
Example 1:
class Test
{
public static void main(String[] args){
int String=10;
System.out.println(String);
}}
Output:
10
Example 2:
class Test
{
public static void main(String[] args){
int Runnable=10;
System.out.println(Runnable);
}}
Output:
10
| Identifiers | Description | Example |
|---|---|---|
| Variable Identifier | A name given to a variable to uniquely identify it within the program. | int age; |
| Method Identifier | A name given to a method (function) to uniquely identify it within the program. | void printMessage() { ... } |
| Class Identifier | A name given to a class to uniquely identify it within the program. | public class MyClass { ... } |
| Package Identifier | A name given to a package to uniquely identify it within the program. | package com.example.myapp; |
| Interface Identifier | A name given to an interface to uniquely identify it within the program. | public interface MyInterface { ... } |
| Constant Identifier | A name given to a constant value that cannot be changed during the execution of the program. | final int MAX_VALUE = 100; |
| Label Identifier | A name given to a label used for flow control statements like loops or branches. | outerLoop: for (int i = 0; i < 5; i++) { ... } |
| Enum Identifier | A name given to an enumerated type to define a set of named values. | enum Color { RED, GREEN, BLUE } |
| Type Parameter Identifier | A name given to a type parameter in generic classes or methods. | class MyGenericClass<T> { ... } |