Accessing arguments in Java - Interactive Code Practice

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(args[[1]]);
    }
}

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

Alength

B0

C1

Dargs

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 as the index.

Trying to print args directly instead of an element.

The first argument in the args array is at index 0.

2fill in blank

medium

Complete the code to check if any arguments were passed.

Java

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

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

Acount

Blength()

Csize()

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using length() which is for Strings, not arrays.

Using size() which is for collections, not arrays.

The args array has a length property (no parentheses) to get its size.

3fill in blank

hard

Fix the error in the code to print all arguments using a for loop.

Java

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

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

Alength

Blength()

Ccount

Dsize()

Attempts:

3 left

💡 Hint

Common Mistakes

Using length() which causes a compile error.

Using size() which is not valid for arrays.

Arrays use length without parentheses to get their size.

4fill in blank

hard

Fill both blanks to print the last argument safely.

Java

public class Main {
    public static void main(String[] args) {
        if (args.[1] > 0) {
            System.out.println(args[args.[2] - 1]);
        } else {
            System.out.println("No arguments.");
        }
    }
}

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

Alength

Bsize

Clength()

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using length() which is invalid for arrays.

Using size or count which do not exist for arrays.

Use args.length to check the number of arguments and to access the last one.

5fill in blank

hard

Fill all three blanks to print all arguments in uppercase.

Java

public class Main {
    public static void main(String[] args) {
        for (int [1] = 0; [2] < args.[3]; [1]++) {
            System.out.println(args[[1]].toUpperCase());
        }
    }
}

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

Ai

Bj

Clength

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Using size instead of length for arrays.

Use i as the loop variable and args.length for the array size.

Practice

1. What is the correct way to access the first command-line argument in a Java program inside the main method?

easy

A. args.first()

B. args[0]

C. args(0)

D. args.get(0)

Solution

1. Step 1: Understand the type of args

   The args parameter in main is an array of strings.

2. Step 2: Access array elements in Java

   Array elements are accessed using square brackets with the index inside, starting at 0.

3. Final Answer:

   args[0] -> Option B

4. Quick Check:

   Array access uses square brackets [OK]

Hint: Use square brackets to access array elements in Java [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Trying to call methods like first() on array
• Using get() which is for lists, not arrays

2. Which of the following is the correct signature of the main method to access command-line arguments in Java?

easy

A. public void main(String[] args)

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

C. static public void main(String args)

D. public static void 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: Check each option

   public static void main(String args[]) matches the correct signature. public void main(String[] args) is missing static. static public void main(String args) has wrong parameter type. public static int main(String[] args) returns int which is invalid.

3. Final Answer:

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

4. Quick Check:

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

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

Common Mistakes:

• Omitting static keyword
• Wrong return type
• Using single String instead of String array

3. What will be the output of the following Java program if run with arguments java Program Hello World?

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

medium

A. 3
World

B. 2
Hello

C. 2
World

D. 3
Hello

Solution

1. Step 1: Count the command-line arguments

   The program is run with two arguments: "Hello" and "World", so args.length is 2.

2. Step 2: Access the second argument

   args[1] is the second argument, which is "World".

3. Final Answer:

   2 World -> Option C

4. Quick Check:

   args.length=2, args[1]=World [OK]

Hint: args.length counts arguments; args[1] is second argument [OK]

Common Mistakes:

• Counting program name as argument
• Using args[0] as second argument
• Confusing args.length with number of arguments plus one

4. Identify the error in the following Java program that tries to print the first command-line argument:

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

medium

A. Using parentheses instead of square brackets to access array element

B. Missing static keyword in main method

C. Incorrect class name

D. Missing return statement in main

Solution

1. Step 1: Check how array elements are accessed

   In Java, array elements are accessed using square brackets, not parentheses.

2. Step 2: Identify the error in the code

   The code uses args(0) which is invalid syntax and causes a compile error.

3. Final Answer:

   Using parentheses instead of square brackets to access array element -> Option A

4. Quick Check:

   Array access uses square brackets [OK]

Hint: Use square brackets [] for arrays, not parentheses () [OK]

Common Mistakes:

• Using parentheses for array access
• Confusing method call syntax with array access
• Ignoring compile errors due to wrong syntax

5. You want to write a Java program that prints all command-line arguments separated by commas. Which code snippet correctly does this inside main?

hard

A. for(int i=0; i

B. for(String arg : args) {
System.out.print(arg + ", ");
}

C. int i = 0;
while(i <= args.length) {
System.out.print(args[i] + ", ");
i++;
}

D. for(int i=1; i<=args.length; i++) {
System.out.print(args[i] + ", ");
}

Solution

1. Step 1: Understand the goal

   We want to print all arguments separated by commas without trailing comma.

2. Step 2: Analyze each option

   for(int i=0; i

3. Final Answer:

   for(int i=0; i<args.length; i++) { System.out.print(args[i] + (i < args.length - 1 ? ", " : "")); } -> Option A

4. Quick Check:

   Loop with index and conditional comma [OK]

Hint: Use index loop and add comma only if not last element [OK]

Common Mistakes:

• Adding comma after last argument
• Off-by-one errors in loops
• Accessing array out of bounds