Syntax for command line arguments in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the main method that accepts command line arguments.

Java

public static void [1](String[] args) { }

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

Amain

Bstart

Crun

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name other than 'main' for the entry point.

The main method in Java that accepts command line arguments must be named main.

2fill in blank

medium

Complete the code to print the first command line argument.

Java

System.out.println(args[1]);

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

A[0]

B(0)

C{0}

D<0>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or braces instead of square brackets to access array elements.

Command line arguments are stored in an array, accessed by index with square brackets.

3fill in blank

hard

Fix the error in the main method declaration to accept command line arguments.

Java

public static void main([1] args) { }

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

AString

Bstring

CString[]

DString args[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'string' instead of 'String'.

Declaring a single String instead of an array.

The main method must accept an array of Strings, declared as String[] args.

4fill in blank

hard

Fill both blanks to declare the main method with command line arguments and print the number of arguments.

Java

public static void [1](String[] [2]) {
    System.out.println([2].length);
}

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

Amain

Bargs

Cargv

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names or parameter names.

Trying to print length of a non-array variable.

The main method is named main and the parameter name is commonly args. The length property gives the number of arguments.

5fill in blank

hard

Fill all three blanks to declare main, access the second argument, and print it.

Java

public static void [1](String[] [2]) {
    System.out.println([2][3]);
}

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

Amain

Bargs

C[1]

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 0 instead of 1 to access the second argument.

Using wrong method or parameter names.

The main method is named main, the parameter is args, and the second argument is accessed with index 1.

Practice

1. What is the correct way to declare the main method to accept command line arguments in Java?

easy

A. public void main(String args)

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

C. static void main(String args[])

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

Solution

1. Step 1: Understand 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 exactly. Others either miss static, have wrong return type, or wrong parameter type.

3. Final Answer:

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

4. Quick Check:

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

Hint: Main method always: public static void main(String[] args) [OK]

Common Mistakes:

• Omitting static keyword
• Using wrong parameter type
• Changing return type from void

2. Which of the following is the correct way to access the first command line argument inside the main method?

easy

A. args[0]

B. args.first()

C. args.get(0)

D. args(0)

Solution

1. Step 1: Recall how arrays are accessed in Java

   Java arrays use square brackets [] with zero-based indexing to access elements.

2. Step 2: Evaluate options

   Only args[0] uses correct syntax. args(0) and args.get(0) are invalid for arrays, and args.first() is not a method for arrays.

3. Final Answer:

   args[0] -> Option A

4. Quick Check:

   Array access uses square brackets = args[0] [OK]

Hint: Use square brackets to access array elements: args[0] [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Trying to call methods on array
• Confusing with List syntax

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

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

medium

A. 2
Hello
World

B. 3
Hello
World

C. 2
World
Hello

D. 3
World
Hello

Solution

1. Step 1: Count command line arguments

   Arguments are "Hello" and "World", so args.length is 2.

2. Step 2: Check printed values

   args[0] is "Hello", args[1] is "World". So output lines are 2, Hello, World.

3. Final Answer:

   2 Hello World -> Option A

4. Quick Check:

   args.length=2, args[0]=Hello, args[1]=World [OK]

Hint: args.length counts arguments; args[0] is first argument [OK]

Common Mistakes:

• Counting program name as argument
• Swapping args[0] and args[1]
• Assuming args.length includes program name

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

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

medium

A. System.out.println should use args(i) instead of args[i]

B. args should be declared as int[] not String[]

C. Loop starts at 1 and uses <= causing ArrayIndexOutOfBoundsException

D. main method must return int, not void

Solution

1. Step 1: Analyze loop indexing

   The loop starts at i=1 and runs while i <= args.length. Array indices go from 0 to args.length-1.

2. Step 2: Identify error cause

   Accessing args[args.length] causes ArrayIndexOutOfBoundsException. Also, skipping args[0] misses first argument.

3. Final Answer:

   Loop starts at 1 and uses <= causing ArrayIndexOutOfBoundsException -> Option C

4. Quick Check:

   Array indices 0 to length-1, loop must use i=0 to i<length [OK]

Hint: Loop from 0 to args.length-1 to avoid index errors [OK]

Common Mistakes:

• Starting loop at 1 instead of 0
• Using <= instead of < in loop condition
• Using parentheses instead of brackets for array access

5. You want to write a Java program that sums two integers passed as command line arguments and prints the result. Which code snippet correctly parses and sums the arguments?

hard

A. int sum = Integer.parseInt(args[0]) + args[1].parseInt(); System.out.println(sum);

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

C. int sum = Integer.valueOf(args[0]) + args[1]; System.out.println(sum);

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

Solution

1. Step 1: Convert String arguments to integers

   Use Integer.parseInt() to convert each String argument to int.

2. Step 2: Sum the parsed integers and print

   Sum the two parsed ints and print the result using System.out.println.

3. Final Answer:

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

4. Quick Check:

   Parse strings to int with Integer.parseInt() before adding [OK]

Hint: Parse args with Integer.parseInt() before arithmetic [OK]

Common Mistakes:

• Adding strings directly without parsing
• Using wrong method to parse integers
• Calling parseInt() on string variable incorrectly