Reading integer input in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read an integer from the user using Scanner.

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int number = scanner.[1]();
        System.out.println("You entered: " + number);
    }
}

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

AnextLine

BnextDouble

CnextInt

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using nextLine() which reads a whole line as a string.

Using nextDouble() which reads a decimal number.

The nextInt() method reads an integer value from the user input.

2fill in blank

medium

Complete the code to create a Scanner object to read input from the keyboard.

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner [1] = new Scanner(System.in);
    }
}

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

Areader

Binput

Ckeyboard

Dscanner

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that conflicts with class names.

Using reserved keywords as variable names.

Variable names can be anything, but scanner is a common and clear choice.

3fill in blank

hard

Fix the error in the code to correctly read an integer from the user.

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int number = scanner.[1]();
        System.out.println("Number: " + number);
    }
}

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

AnextDouble

BnextInt

CnextLine

DnextFloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using nextLine() and trying to assign to int causes errors.

Using nextDouble() when expecting an integer.

The method nextInt() reads an integer. Using nextLine() or others causes errors or wrong types.

4fill in blank

hard

Fill both blanks to read an integer and print it with a message.

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner [1] = new Scanner(System.in);
        int num = [2].nextInt();
        System.out.println("You typed: " + num);
    }
}

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

Ascanner

Binput

Creader

Dkeyboard

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Forgetting to create the Scanner object.

Using the same variable name scanner to create and then call nextInt() is correct.

5fill in blank

hard

Fill all three blanks to read two integers and print their sum.

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner [1] = new Scanner(System.in);
        int a = [2].nextInt();
        int b = [3].nextInt();
        System.out.println("Sum: " + (a + b));
    }
}

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

Ascanner

Binput

Creader

Dkeyboard

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for reading inputs.

Not creating the Scanner object before reading.

Use the same Scanner variable scanner to read both integers.

Practice

1.

Which Java class is commonly used to read integer input from the user?

easy

A. FileReader

B. BufferedReader

C. Scanner

D. PrintWriter

Solution

1. Step 1: Identify the class for input reading

   The Scanner class is designed to read input from various sources including user input.

2. Step 2: Confirm the class for integer input

   Scanner provides the nextInt() method to read integers specifically.

3. Final Answer:

   Scanner -> Option C

4. Quick Check:

   Input class = Scanner [OK]

Hint: Use Scanner class to read integers easily [OK]

Common Mistakes:

• Confusing Scanner with FileReader which reads files
• Using PrintWriter which is for output, not input
• Thinking BufferedReader reads integers directly without parsing

2.

Which of the following is the correct way to create a Scanner object to read from the keyboard?

?

easy

A. Scanner input = new Scanner(System.console());

B. Scanner input = new Scanner(System.out);

C. Scanner input = new Scanner(System.err);

D. Scanner input = new Scanner(System.in);

Solution

1. Step 1: Understand input source for Scanner

   To read user input from the keyboard, System.in is used as the input stream.

2. Step 2: Match correct Scanner constructor

   The correct syntax is new Scanner(System.in). Other options use output or error streams, which are incorrect.

3. Final Answer:

   Scanner input = new Scanner(System.in); -> Option D

4. Quick Check:

   Keyboard input = System.in [OK]

Hint: Use System.in with Scanner for keyboard input [OK]

Common Mistakes:

• Using System.out or System.err instead of System.in
• Trying to use System.console() which returns Console, not InputStream
• Forgetting to import java.util.Scanner

3.

What will be the output of the following Java code if the user enters 42?

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        System.out.println(num + 10);
        sc.close();
    }
}

medium

A. 52

B. 42

C. 10

D. Error at runtime

Solution

1. Step 1: Read integer input

   The program reads an integer from the user using nextInt(). User inputs 42, so num = 42.

2. Step 2: Add 10 and print result

   The program prints num + 10, which is 42 + 10 = 52.

3. Final Answer:

   52 -> Option A

4. Quick Check:

   42 + 10 = 52 [OK]

Hint: Add 10 to input number and print [OK]

Common Mistakes:

• Printing input without adding 10
• Forgetting to close Scanner (not an error but good practice)
• Assuming input is string, causing error

4.

Identify the error in the following code snippet that reads an integer from the user:

import java.util.Scanner;

public class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextLine();
        System.out.println(number);
        sc.close();
    }
}

medium

A. Scanner object is not closed properly.

B. Using nextLine() to read an integer causes a type mismatch error.

C. Missing import statement for Scanner.

D. System.out.println() cannot print integers.

Solution

1. Step 1: Check method used to read input

   The code uses nextLine() which returns a String, but tries to assign it to an int variable.

2. Step 2: Understand type mismatch

   Assigning a String to an int variable causes a compile-time error. The correct method to read an int is nextInt().

3. Final Answer:

   Using nextLine() to read an integer causes a type mismatch error. -> Option B

4. Quick Check:

   nextLine() returns String, not int [OK]

Hint: Use nextInt() to read integers, not nextLine() [OK]

Common Mistakes:

• Using nextLine() instead of nextInt() for integers
• Ignoring type mismatch errors
• Not closing Scanner (though not the main error here)

5.

You want to read two integers from the user and print their sum. Which code snippet correctly does this?

?

hard

A. Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
int b = sc.nextInt();
System.out.println(a + b);
sc.close();

B. Scanner sc = new Scanner(System.in);
int a = Integer.parseInt(sc.nextLine());
int b = sc.nextLine();
System.out.println(a + b);

C. Scanner sc = new Scanner(System.in);
String a = sc.nextLine();
String b = sc.nextLine();
System.out.println(a + b);
sc.close();

D. Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
String b = sc.nextLine();
System.out.println(a + b);
sc.close();

Solution

1. Step 1: Identify the correct code for reading two integers

   Scanner sc = new Scanner(System.in); int a = sc.nextInt(); int b = sc.nextInt(); System.out.println(a + b); sc.close(); uses sc.nextInt() twice to read integers directly, handling whitespace or newlines, then prints their sum.

2. Step 2: Eliminate incorrect options

   A: Compile error - int b = sc.nextLine(); (String to int).
   C: Concatenates strings ("1" + "2" = "12").
   D: nextLine() after nextInt() reads leftover newline (b = "", e.g., 5 + "" = "5").

3. Final Answer:

   Scanner sc = new Scanner(System.in); int a = sc.nextInt(); int b = sc.nextInt(); System.out.println(a + b); sc.close(); -> Option A

4. Quick Check:

   Two nextInt() reads ints correctly [OK]

Hint: Use nextInt() for integer input reliably [OK]

Common Mistakes:

• Mixing nextInt() and nextLine() causing input skipping
• Adding strings instead of integers
• Not closing Scanner after use