Keywords and Identifiers in Java

Introduction

In Java, keywords and identifiers play a crucial role in defining the structure and behavior of programs. Keywords have predefined meanings in the language, while identifiers are names given to elements such as variables, methods, and classes.

Keywords in Java

Keywords are reserved words in Java that have specific meanings and cannot be used for identifiers. Examples include:

  • class: Used to define a class.
  • public: Specifies access level as public.
  • static: Denotes a method or variable that belongs to the class, not an instance.
  • void: Specifies that a method does not return a value.
  • if: Starts a conditional statement.
  • return: Exits from a method and optionally returns a value.

Java keywords are case-sensitive and must be written in lowercase.

Identifiers in Java

Identifiers are the names used to identify variables, methods, classes, or objects. They must follow certain rules:

  • Identifiers can consist of letters, digits, underscores (_), and dollar signs ($).
  • They cannot begin with a digit.
  • They cannot be the same as a Java keyword.
  • Identifiers are case-sensitive.
  • There is no length limit for identifiers.

Example: Keywords and Identifiers

Step 1: Write the Program

Create a file named KeywordsAndIdentifiers.java and write the following code:

    public class KeywordsAndIdentifiers {
        // Variable identifiers
        int age = 25; // 'age' is an identifier
        String name = "Alice"; // 'name' is an identifier
    
        // Method identifier
        public void displayInfo() {
            // Keyword 'System' and 'out'
            System.out.println("Name: " + name);
            System.out.println("Age: " + age);
        }
    
        // Main method (entry point)
        public static void main(String[] args) {
            // Class identifier
            KeywordsAndIdentifiers obj = new KeywordsAndIdentifiers();
            obj.displayInfo();
        }
    }

Step 2: Compile the Program

Open the terminal or command prompt, navigate to the file location, and type:

    javac KeywordsAndIdentifiers.java

Step 3: Run the Program

Type the following command to execute the program:

    java KeywordsAndIdentifiers

You should see the output:

    Name: Alice
    Age: 25

Conclusion

Keywords and identifiers are essential for writing Java programs. Understanding their rules and usage helps in creating clear and efficient code. Avoid using keywords as identifiers and follow naming conventions for better readability.




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