Command Line Arguments in Java Interview Questions

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Introduction

Command Line Arguments in Java are used to pass data to a program at the time of execution. These arguments are provided through the command line and received by the Java program using the String[] args parameter of the main method. This mechanism allows programs to behave dynamically without changing source code. In Java interviews, command line arguments are commonly used to test understanding of program execution flow, the role of the main method, and how runtime input differs from user input mechanisms like Scanner. A clear understanding of this topic reflects strong fundamentals of Java application startup and execution.

What Interviewers Expect From This Topic

  • Clear understanding of how command line arguments are passed and accessed
  • Ability to explain the role of String[] args in main method
  • Difference between command line arguments and user input
  • Knowledge of runtime behavior and argument indexing
  • Awareness of common mistakes and edge cases

Table of Contents

  • Interview Questions
  • Scenario-Based Interview Questions
  • Common Mistakes
  • FAQs

Interview Questions

Q1. What are command line arguments in Java?

Command line arguments are values passed to a Java program during execution through the command line.

  • They are provided when the program starts
  • They allow dynamic input without code changes
  • Received using the String[] args parameter

Q2. How are command line arguments passed to a Java program?

Command line arguments are passed after the class name during program execution.

  • Provided in the command prompt or terminal
  • Separated by spaces
  • Automatically stored in args array

Q3. Where are command line arguments stored in Java?

Command line arguments are stored in the String[] args array of the main method.

  • Each argument is stored as a string
  • Indexing starts from zero

Q4. Why are command line arguments stored as strings?

All command line arguments are treated as strings by the JVM.

  • Command line input is textual by nature
  • Type conversion must be done manually if needed

Q5. What is the role of String[] args in the main method?

String[] args acts as a container for command line arguments.

  • Receives runtime input from command line
  • Allows access to arguments inside the program

Q6. Can we change the name of args in main method?

Yes, the parameter name can be changed.

  • Name is not significant to JVM
  • Only type and structure matter

Q7. Can we pass numbers as command line arguments?

Yes, numbers can be passed but they are received as strings.

  • Explicit parsing is required
  • For example, Integer.parseInt()

Q8. What happens if no command line arguments are passed?

The args array will be empty.

  • Length of args will be zero
  • No runtime error occurs

Q9. Can command line arguments be null?

No, args is never null when main method is executed.

  • It is initialized as an empty array if no arguments are provided

Q10. What is args.length used for?

args.length is used to determine the number of command line arguments.

  • Helps in validating input
  • Prevents ArrayIndexOutOfBoundsException

Q11. How do you access individual command line arguments?

Individual arguments are accessed using array indexing.

  • args[0] for first argument
  • args[1] for second argument

Q12. Difference between command line arguments and Scanner input?

Command line arguments and Scanner input differ in how input is provided.

Aspect Command Line Arguments Scanner Input
Input Time At program start During program execution
Interaction Non-interactive Interactive
Use Case Configuration values User-driven input

Q13. Can command line arguments contain spaces?

Yes, but they must be enclosed in quotes.

  • Without quotes, spaces split arguments

Q14. Are command line arguments supported in IDEs?

Yes, IDEs provide configuration options to pass arguments.

  • Configured in run settings
  • Passed to main method at runtime

Q15. Can command line arguments be used in enterprise applications?

Yes, they are often used for configuration and environment setup.

  • Passing file paths
  • Environment flags

Scenario-Based Interview Questions

Scenario 1: Program throws ArrayIndexOutOfBoundsException

This occurs when accessing args index without validating args.length.

Scenario 2: Need to pass environment-specific values

Command line arguments can be used to pass environment-specific configuration values.

Scenario 3: Program needs runtime configuration without code change

Command line arguments are suitable for this requirement.

Common Mistakes

  • Assuming args is null when no arguments are passed
  • Not validating args.length before access
  • Forgetting to parse numeric values
  • Confusing command line arguments with user input

Quick Revision Snapshot

  • Arguments are passed at program start
  • Received via String[] args
  • All arguments are strings
  • args.length gives argument count
  • Used for runtime configuration

FAQs

Are command line arguments mandatory?

No, programs can run without command line arguments.

Can we change the data type of args?

No, it must always be String array for JVM recognition.

Are command line arguments secure?

They are visible to users and should not contain sensitive data.

Conclusion

Command Line Arguments in Java provide a simple and effective way to pass runtime data to applications. Understanding how they work is essential for Java interviews, especially when discussing program execution, main method behavior, and runtime configuration. Proper handling of command line arguments improves program flexibility and robustness.

Next recommended topic: Java Input and Output Basics

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