Using Scanner class in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Reading an integer and a string using Scanner

What is the output of this Java program when the user inputs:
42
Hello

Java

import java.util.Scanner;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int num = sc.nextInt();
    sc.nextLine();
    String text = sc.nextLine();
    System.out.println("Number: " + num);
    System.out.println("Text: " + text);
  }
}

A

Number: 42
Text: Hello

B

Number: 42
Text: 

C

Number: 42
Text: \nHello

D

Number: 42
Text: null

💡 Hint

Remember that nextInt() does not consume the newline character.

The nextInt() method reads the integer but leaves the newline character in the input buffer. The nextLine() then reads that leftover newline as an empty string. So the text variable is empty.

❓ Predict Output

intermediate

Reading multiple tokens with Scanner

What will be the output of this program if the user inputs:
John 25 true

Java

import java.util.Scanner;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String name = sc.next();
    int age = sc.nextInt();
    boolean isStudent = sc.nextBoolean();
    System.out.println(name + ", " + age + ", " + isStudent);
  }
}

A John 25 true

B Compilation error

C John, 25, false

D John, 25, true

💡 Hint

next() reads one word, nextInt() reads an integer, nextBoolean() reads true/false.

The Scanner reads tokens separated by whitespace. next() reads "John", nextInt() reads 25, nextBoolean() reads true. The output concatenates them with commas.

🔧 Debug

advanced

Why does this Scanner code skip input?

This code is supposed to read an integer and then a full line of text. But it skips reading the text input. Why?
Identify the problem and select the correct explanation.

Java

import java.util.Scanner;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter number: ");
    int n = sc.nextInt();
    sc.nextLine();
    System.out.print("Enter text: ");
    String line = sc.nextLine();
    System.out.println("Number: " + n);
    System.out.println("Text: " + line);
  }
}

A nextLine() cannot be used after nextInt() because it causes an infinite loop.

B nextInt() leaves a newline in the buffer, so nextLine() reads it as empty.

C The Scanner object must be closed before reading the next line.

D The program needs to call sc.next() before nextLine() to clear the buffer.

💡 Hint

Think about what happens to the newline character after nextInt().

nextInt() reads only the integer but leaves the newline character. nextLine() then reads that leftover newline as an empty string, causing it to skip the actual input.

📝 Syntax

advanced

Identify the syntax error in Scanner usage

Which option contains a syntax error when trying to read a double value using Scanner?

A double d = sc.nextDouble();

B double d = sc.nextDouble("");

C double d = sc.nextDouble;

D double d = sc.nextdouble();

💡 Hint

Method names in Java are case-sensitive.

Option B is invalid because nextDouble() does not take any arguments. Option C is invalid because nextDouble is a method and must be called with parentheses. Option D is invalid because method names are case-sensitive; nextdouble() is not defined.

🚀 Application

expert

How many tokens are read by Scanner?

Given this input line:
apple, banana; cherry orange
and this code:
Scanner sc = new Scanner(System.in); sc.useDelimiter(",|;| "); int count = 0; while(sc.hasNext()) { sc.next(); count++; } System.out.println(count);
What is the output?

Java

import java.util.Scanner;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    sc.useDelimiter(",|;| ");
    int count = 0;
    while(sc.hasNext()) {
      sc.next();
      count++;
    }
    System.out.println(count);
  }
}

A 4

B 3

C 5

D 6

💡 Hint

Count the words separated by comma, semicolon, or space.

The delimiters split the input on ",", ";", or space. Scanner skips consecutive delimiters (like ", " or "; "), so the tokens are "apple", "banana", "cherry", "orange" = 4 tokens.