What are Identifiers in Java?

What are Identifiers in Java?

7 mins readComment
Esha
Esha Gupta
Associate Senior Executive
Updated on May 8, 2024 15:48 IST

Have you ever wondered how Java keeps everything organized and accessible? It's all because of identifiers. Those unique labels assigned to variables, methods, and classes. These crucial elements of Java programming follow specific naming rules and help make the code clear, efficient, and error-free. Let's understand more!

Identifiers in Java are the names which act as labels that allow the programmer to refer to and manipulate these elements within the code. Identifiers must follow specific rules, like starting with a letter, underscore, or dollar sign, and they can include alphanumeric characters. In this blog, we will learn everything about identifiers in Java!

Table of Contents

What are Identifiers in Java?

In Java, identifiers are the names given to various programming elements such as classes, methods, variables, and objects. These identifiers are used for identification purposes and play a crucial role in the readability and maintainability of the code. They are used to uniquely identify each element in the code, ensuring that each element is distinctly recognizable. Java is case-sensitive, which means that identifiers like myVariable, MyVariable, and MYVARIABLE are considered different from each other.

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Rules For Defining Java Identifiers

There are specific rules to follow when defining these identifiers.

1. Alphanumeric Characters: Identifiers can include letters (A-Z and a-z), digits (0-9), underscore (_), and dollar sign ($). However, they must start with a letter, an underscore or a dollar sign. They cannot begin with a digit.

2. Case Sensitivity: Java is case-sensitive, meaning MyIdentifier and myidentifier would be recognized as distinct identifiers.

3. No Reserved Words: Identifiers cannot be Java reserved words or keywords. For example, you cannot name a variable int or class as these are reserved by the language.

4. No Special Characters: Apart from underscore and dollar sign, no other special characters or spaces are allowed in identifiers.

5. Length Limitation: Technically, there is no limit on the length of an identifier in Java. However, it's advisable to keep them concise for the sake of readability and maintainability of the code.

 

Best Practices for Naming

Some widely recognized best practices for naming in Java are given below.

1. Use Meaningful Names: Choose names that clearly and intuitively describe the purpose of the variable, method, or class. For example, use employeeSalary instead of vague names like es or data.

2. Follow Naming Conventions: Adhere to Java's standard naming conventions -

  • Classes and Interfaces: Use CamelCase with the first letter capitalized, e.g. Student, BankAccount.
  • Methods and Variables: Use lowerCamelCase, e.g. calculateSalary, firstName.
  • Constants: Use all uppercase letters with underscores to separate words, e.g. MAX_SIZE, DEFAULT_VALUE.

3. Start with a Letter: Although underscores and dollar signs are allowed, it's standard practice to start names with a letter.

4. Avoid Using Single Characters: Except for temporary and loop variables (like i, j, x, y), avoid single-character names. Descriptive names make the code more understandable.

5. Be Consistent: Use consistent naming patterns throughout your codebase. This consistency helps others understand the structure and purpose of your code more quickly.

6. Avoid Abbreviations and Acronyms: Avoid using abbreviations unless the abbreviation is more widely known than the full word (like URL). They can make the code less readable, especially for those unfamiliar with the abbreviations.

7. Differentiate Clearly: Avoid using names that differ only by number or case, e.g. user1, user2, or User, user, as they can be easily confused.

8. Use Pronounceable Names: Names that can be pronounced are generally easier to discuss, which can be important during team discussions or code reviews.

9. Context Matters: Use names that provide enough information about their use. For instance, saveEmployeeData is more informative than just saveData.

10. Avoid Redundancy and Noise Words: Avoid redundant information that doesn’t add clarity, e.g. Customer class doesn’t need variables like customerName. Just the name is sufficient.

See the list of reserved words/keywords in Java below

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Table on Valid and Invalid Identifiers in Java

Here's a table on valid and invalid identifiers in Java for a quick glance for our readers!

Criteria

Valid Identifiers

Invalid Identifiers

Start with a letter, underscore (_), or dollar sign ($)

myVariable, _value, $id

9pins, -name

Subsequent characters

var1, i9, _1_value

a@b, hello!world

Case Sensitivity

myVariable, MyVariable

(Case variations are valid but represent different identifiers)

No reserved words

userInput, totalSum

class, int, void

Unlimited length (practically reasonable)

longIdentifierName123

(No length-based invalidity, but very long names are discouraged for readability)

Examples Where Identifiers in Java are Commonly Used

Let's see some examples to understand the concept better.

Example 1: Student Class and Objects

Problem Statement: Create a Student class with instance variables for student details and a method to display these details. Then, create and display the details of a student.


 
public class Student {
// Instance variables (identifiers for student details)
String name;
int age;
double grade;
// Constructor to initialize the student details
public Student(String name, int age, double grade) {
this.name = name;
this.age = age;
this.grade = grade;
}
// Method to display student information
public void displayInfo() {
System.out.println("Name: " + name + ", Age: " + age + ", Grade: " + grade);
}
public static void main(String[] args) {
// Creating a Student object with identifiers
Student student1 = new Student("Esha", 20, 9.5);
student1.displayInfo(); // Displaying the student's information
}
}
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Output

Name: Esha, Age: 20, Grade: 9.5

The program defines a Student class with identifiers name, age, and grade. A Student object named student1 is created and initialized with specific details. The displayInfo method then prints these details.

Example 2: Bank Account with Deposit and Withdraw Methods

Problem Statement: Implement a BankAccount class with methods to deposit and withdraw funds and an instance variable to track the account balance.


 
public class BankAccount {
// Instance variable (identifier for account balance)
private double balance;
// Constructor to initialize the balance
public BankAccount(double initialBalance) {
this.balance = initialBalance;
}
// Method to deposit money
public void deposit(double amount) {
balance += amount;
}
// Method to withdraw money
public void withdraw(double amount) {
balance -= amount;
}
public static void main(String[] args) {
// Creating a bank account with an initial balance
BankAccount account = new BankAccount(1000.0);
account.deposit(500.0); // Depositing money
account.withdraw(200.0); // Withdrawing money
// Identifier 'balance' is used to track the account balance
System.out.println("Current Balance: " + account.balance);
}
}
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Output

Current Balance: 1300.0

In this example, the BankAccount class has an identifier balance that keeps track of the account balance. The deposit and withdraw methods update this balance, and the final balance is displayed in the output.

Example 3: Calculation of Area

Problem Statement: Write a program to calculate the area of a rectangle using local identifiers for length and width.


 
public class AreaCalculator {
// Method to calculate the area of a rectangle
public static double calculateArea(double length, double width) {
double area = length * width; // Local identifier 'area'
return area;
}
public static void main(String[] args) {
double length = 5.0;
double width = 3.0;
double area = calculateArea(length, width); // Using 'area' to store the result
System.out.println("Area of the rectangle: " + area);
}
}
Copy code

Output

Area of the rectangle: 15.0

The calculateArea method uses local identifiers length, width, and area to perform the calculation. The calculated area of the rectangle is then printed.

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Key Takeaways

  • Identifiers in Java are names given to various programming elements such as classes, methods, variables, and objects. They serve as unique references for these elements within the code.
  • Java identifiers are case-sensitive, meaning myVariable and MyVariable are considered distinct identifiers. This feature should be carefully managed to avoid confusion.
  • Adhering to Java's naming conventions improves code readability and maintainability. For instance, class names typically start with uppercase letters, while variable names start with lowercase letters.
  • Keywords and reserved words in Java, such as int, class, or static, cannot be used as identifiers. These words have predefined meanings in the Java programming language.
  • Choosing descriptive and meaningful names for identifiers makes the code more understandable and self-documenting, facilitating easier maintenance and collaboration.

FAQs

What is an Identifier in Java?

An identifier in Java is a name given to elements in a program, such as classes, methods, variables, and labels. They are user-defined names that are used for identification purposes.

What are the Rules for Naming Identifiers in Java?

 In Java, identifiers must follow certain rules:

  • They must begin with a letter (A to Z or a to z), currency character ($), or an underscore (_).
  • Subsequent characters may be letters, currency characters, underscores, or digits (0 to 9).
  • Java identifiers are case-sensitive.
  • They cannot be Java keywords or reserved words.
  • There's no limit on the length of an identifier, but it's recommended to keep it reasonable for readability.

Can Identifiers Start with Numbers in Java?

No, identifiers in Java cannot start with a number. They must begin with a letter, an underscore (_), or a currency character ($).

Are Java Identifiers Case Sensitive?

Yes, Java identifiers are case-sensitive. It means that the identifiers Age, AGE, and age would be considered distinct and different from each other.

Can Java Reserved Words be Used as Identifiers?

No, reserved words in Java, such as int, class, static, etc. cannot be used as identifiers. Reserved words have predefined meanings in the language's syntax and using them as identifiers would lead to confusion and syntax errors.

About the Author
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Esha Gupta
Associate Senior Executive

Hello, world! I'm Esha Gupta, your go-to Technical Content Developer focusing on Java, Data Structures and Algorithms, and Front End Development. Alongside these specialities, I have a zest for immersing myself in v... Read Full Bio