Why command line arguments are used in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the first command line argument.

Java

public class Main {
    public static void main(String[] args) {
        System.out.println([1]);
    }
}

Drag options to blanks, or click blank then click option'

Aargs

Bargs[0]

Cargs.length

Dargs.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Using args instead of args[0] to print the first argument.

The first command line argument is accessed using args[0].

2fill in blank

medium

Complete the code to check if any command line arguments were passed.

Java

public class Main {
    public static void main(String[] args) {
        if ([1] > 0) {
            System.out.println("Arguments passed");
        } else {
            System.out.println("No arguments");
        }
    }
}

Drag options to blanks, or click blank then click option'

Aargs.count

Bargs[0]

Cargs.size()

Dargs.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using args[0] to check length instead of args.length.

The number of command line arguments is given by args.length.

3fill in blank

hard

Fix the error in the code to correctly print all command line arguments.

Java

public class Main {
    public static void main(String[] args) {
        for (int i = 0; i < [1]; i++) {
            System.out.println(args[i]);
        }
    }
}

Drag options to blanks, or click blank then click option'

Aargs.length

Bargs.count()

Cargs.size()

Dargs.length()

Attempts:

3 left

💡 Hint

Common Mistakes

Using args.size() or args.length() which are invalid for arrays.

The correct way to get the number of elements in the args array is args.length.

4fill in blank

hard

Fill both blanks to create a program that sums two integer command line arguments.

Java

public class Main {
    public static void main(String[] args) {
        int num1 = Integer.[1](args[0]);
        int num2 = Integer.[2](args[1]);
        System.out.println(num1 + num2);
    }
}

Drag options to blanks, or click blank then click option'

AparseInt

BvalueOf

CtoString

DparseDouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using valueOf which returns an Integer object, not int.

Use Integer.parseInt() to convert string arguments to integers.

5fill in blank

hard

Fill all three blanks to create a program that prints command line arguments in uppercase if they exist.

Java

public class Main {
    public static void main(String[] args) {
        if (args.[1] > 0) {
            for (int i = 0; i < args.[2]; i++) {
                System.out.println(args[i].[3]());
            }
        } else {
            System.out.println("No arguments");
        }
    }
}

Drag options to blanks, or click blank then click option'

Alength

Bsize

CtoUpperCase

DtoLowerCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using size instead of length for arrays.

Use args.length to get the number of arguments and toUpperCase() to convert strings to uppercase.

Practice

1. Why are command line arguments used in Java programs?

easy

A. To allow users to provide input values when starting the program

B. To change the Java language syntax

C. To make the program run faster

D. To create graphical user interfaces automatically

Solution

1. Step 1: Understand the purpose of command line arguments

   Command line arguments let users give input to a program when it starts, without changing the code.

2. Step 2: Identify the correct use case

   They help programs behave differently based on user input at launch time.

3. Final Answer:

   To allow users to provide input values when starting the program -> Option A

4. Quick Check:

   Command line arguments = user input at start [OK]

Hint: Command line arguments = inputs given when program starts [OK]

Common Mistakes:

• Thinking command line arguments change the language syntax
• Believing they speed up the program
• Confusing them with GUI creation

2. Which of the following is the correct way to declare the main method to receive command line arguments in Java?

easy

A. public static void main(String args[])

B. public void main(String[] args)

C. static public void main()

D. public static int main(String[] args)

Solution

1. Step 1: Recall the standard main method signature

   The main method must be public, static, return void, and accept a String array parameter.

2. Step 2: Match the correct syntax

   public static void main(String args[]) matches the correct syntax: public static void main(String args[]).

3. Final Answer:

   public static void main(String args[]) -> Option A

4. Quick Check:

   Main method signature = public static void main(String args[]) [OK]

Hint: Main method must be public static void with String array [OK]

Common Mistakes:

• Omitting static or public keywords
• Changing return type from void
• Missing String array parameter

3. What will be the output of the following Java program if run with command line arguments: java Test Hello World?

public class Test {
    public static void main(String[] args) {
        System.out.println(args[0] + " " + args[1]);
    }
}

medium

A. args[0] args[1]

B. Hello World

C. World Hello

D. Compilation error

Solution

1. Step 1: Understand command line arguments array

   args[0] is the first argument "Hello", args[1] is the second argument "World".

2. Step 2: Check the print statement

   The program prints args[0] + " " + args[1], which outputs "Hello World".

3. Final Answer:

   Hello World -> Option B

4. Quick Check:

   args[0] + args[1] = Hello World [OK]

Hint: args[0] is first argument, args[1] second [OK]

Common Mistakes:

• Confusing args index order
• Expecting variable names printed literally
• Assuming compilation error without syntax issues

4. Identify the error in this Java program that tries to print command line arguments:

public class Demo {
    public static void main(String args) {
        System.out.println(args[0]);
    }
}

medium

A. The class name must be different from Demo

B. The print statement syntax is incorrect

C. The main method parameter should be a String array, not a single String

D. There is no error; the program runs fine

Solution

1. Step 1: Check main method parameter type

   The main method must accept a String array (String[] args), not a single String.

2. Step 2: Understand impact on args usage

   Using String args means args[0] is invalid because args is not an array, causing a compile error.

3. Final Answer:

   The main method parameter should be a String array, not a single String -> Option C

4. Quick Check:

   Main method parameter = String[] args [OK]

Hint: Main method needs String array parameter [OK]

Common Mistakes:

• Using single String instead of String array
• Ignoring compile errors from wrong parameter
• Thinking print statement is wrong

5. You want to write a Java program that sums two numbers given as command line arguments. Which code snippet correctly converts the arguments and prints the sum?

public class Sum {
    public static void main(String[] args) {
        // Fill in the blanks
    }
}

hard

A. int a = Integer.valueOf(args); int b = Integer.valueOf(args); System.out.println(a + b);

B. int a = args[0]; int b = args[1]; System.out.println(a + b);

C. String a = args[0]; String b = args[1]; System.out.println(a + b);

D. int a = Integer.parseInt(args[0]); int b = Integer.parseInt(args[1]); System.out.println(a + b);

Solution

1. Step 1: Convert command line arguments from String to int

   Use Integer.parseInt(args[0]) and Integer.parseInt(args[1]) to convert the first two arguments to integers.

2. Step 2: Add the integers and print the result

   Sum the two integers and print the result using System.out.println(a + b).

3. Final Answer:

   int a = Integer.parseInt(args[0]); int b = Integer.parseInt(args[1]); System.out.println(a + b); -> Option D

4. Quick Check:

   Convert args to int then add [OK]

Hint: Use Integer.parseInt to convert args before math [OK]

Common Mistakes:

• Trying to add strings directly without conversion
• Using args as int without parsing
• Using Integer.valueOf with wrong parameter