Using Scanner class in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Java

Scanner scanner = new [1](System.in);

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

AInputStream

BScanner

CSystem

DBufferedReader

Attempts:

3 left

💡 Hint

Common Mistakes

Using InputStream instead of Scanner to create the object.

Trying to use System directly as a class to create Scanner.

The Scanner class is used to read input from various sources. To read from the keyboard, you create a Scanner object with System.in as the input stream.

2fill in blank

medium

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

Java

int number = scanner.[1]();

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

AnextInt

BnextLine

CnextDouble

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using nextDouble() when expecting an integer.

To read an integer from the user, use the nextInt() method of Scanner.

3fill in blank

hard

Fix the error in the code to read a string input from the user.

Java

String name = scanner.[1]();

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

AnextIntLine

BnextDouble

CnextInt

DnextLine

Attempts:

3 left

💡 Hint

Common Mistakes

Using nextInt() or nextDouble() which expect numbers.

Using a non-existent method like nextIntLine().

To read a whole line of text including spaces, use nextLine(). Other methods read tokens or numbers.

4fill in blank

hard

Fill both blanks to read a double value and then close the Scanner.

Java

double value = scanner.[1]();
scanner.[2]();

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

AnextDouble

Bclose

CnextInt

DnextLine

Attempts:

3 left

💡 Hint

Common Mistakes

Using nextInt() instead of nextDouble() for double values.

Forgetting to close the Scanner.

Use nextDouble() to read a double value. Always close the Scanner with close() to free resources.

5fill in blank

hard

Fill all three blanks to read a string, an integer, and then print them.

Java

String name = scanner.[1]();
int age = scanner.[2]();
System.out.println([3] + ": " + age);

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

AnextLine

BnextInt

Cname

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using next() instead of nextLine() for reading the name.

Printing a variable that was not declared.

Use nextLine() to read the full name, nextInt() to read the age, and print the name and age together.

Practice

1. What is the primary purpose of the Scanner class in Java?

easy

A. To write output to the console

B. To handle file operations

C. To create graphical user interfaces

D. To read input from the user

Solution

1. Step 1: Understand Scanner's role

   The Scanner class is designed to read input from various sources, commonly from the user via the keyboard.

2. Step 2: Differentiate from other classes

   Writing output is done by System.out, GUI creation uses other libraries, and file handling uses classes like FileReader.

3. Final Answer:

   To read input from the user -> Option D

4. Quick Check:

   Scanner reads input = B [OK]

Hint: Scanner reads user input from keyboard easily [OK]

Common Mistakes:

• Confusing Scanner with output classes
• Thinking Scanner creates GUI
• Assuming Scanner handles files only

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.in);

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

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

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

Solution

1. Step 1: Identify correct Scanner constructor

   The Scanner constructor requires an InputStream to read input. System.in is the standard input stream (keyboard).

2. Step 2: Check other options

   System.out and System.err are output streams, not input. System.in.read() returns an int, not an InputStream.

3. Final Answer:

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

4. Quick Check:

   Use System.in for input Scanner [OK]

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

Common Mistakes:

• Using System.out or System.err instead of System.in
• Passing System.in.read() which is an int, not InputStream
• Missing 'new' keyword

3. What will be the output of the following code if the user inputs the number 25?

import java.util.Scanner;
public class Test {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int num = sc.nextInt();
    System.out.println(num * 2);
    sc.close();
  }
}

medium

A. Error at runtime

B. 25

C. 50

D. 0

Solution

1. Step 1: Understand input reading

   The program reads an integer from the user using nextInt(). User inputs 25, so num = 25.

2. Step 2: Calculate output

   The program prints num * 2, which is 25 * 2 = 50.

3. Final Answer:

   50 -> Option C

4. Quick Check:

   Input 25 * 2 = 50 [OK]

Hint: Multiply input number by 2 to get output [OK]

Common Mistakes:

• Confusing input with output
• Forgetting to multiply by 2
• Not closing Scanner (though not causing output error)

4. Identify the error in the following code snippet:

import java.util.Scanner;
public class Demo {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter your name:");
    String name = sc.nextInt();
    System.out.println("Hello, " + name);
    sc.close();
  }
}

medium

A. Not closing the Scanner

B. Using nextInt() to read a String

C. Missing import statement for Scanner

D. Incorrect print statement syntax

Solution

1. Step 1: Check input method used

   The code uses nextInt() to read the user's name, which is a String, not an integer.

2. Step 2: Identify correct method

   To read a String, nextLine() or next() should be used instead of nextInt().

3. Final Answer:

   Using nextInt() to read a String -> Option B

4. Quick Check:

   Use nextLine() for String input, not nextInt() [OK]

Hint: Use nextLine() for strings, nextInt() for numbers [OK]

Common Mistakes:

• Using nextInt() for String input
• Ignoring Scanner import
• Not closing Scanner (not error here)
• Misunderstanding print syntax

5. You want to read a full line of text including spaces from the user after reading an integer using Scanner. Which sequence of method calls correctly handles this without skipping input?

Scanner sc = new Scanner(System.in);
int age = sc.nextInt();
// What next?

hard

A. sc.nextLine(); String name = sc.nextLine();

B. String name = sc.nextLine();

C. sc.next(); String name = sc.nextLine();

D. sc.nextInt(); String name = sc.nextLine();

Solution

1. Step 1: Understand Scanner behavior after nextInt()

   After nextInt(), the newline character remains in the input buffer, so a direct nextLine() reads that leftover newline.

2. Step 2: Consume leftover newline before reading full line

   Calling sc.nextLine() once consumes the leftover newline, then the next nextLine() reads the actual full line input.

3. Final Answer:

   sc.nextLine(); String name = sc.nextLine(); -> Option A

4. Quick Check:

   Consume newline with nextLine() before reading full line [OK]

Hint: Call nextLine() twice after nextInt() to read full line [OK]

Common Mistakes:

• Skipping the first nextLine() to consume newline
• Using next() which reads only one word
• Calling nextInt() again unnecessarily