Reading string input in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Java code reading a string?

Consider the following Java code that reads a string from the user and prints it back. What will be printed if the user inputs Hello World?

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.next();
        System.out.println(input);
        scanner.close();
    }
}

A World

B Hello World

C Hello

D Compilation error

💡 Hint

Remember that scanner.next() reads input only until the first space.

The method scanner.next() reads only the next token, which is the sequence of characters until the first whitespace. So it reads "Hello" and stops before the space.

❓ Predict Output

intermediate

What does this code print when reading a full line?

This Java code reads a full line of input from the user. What will it print if the user inputs Hello World?

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine();
        System.out.println(input);
        scanner.close();
    }
}

A World

B Hello World

C Hello

D Runtime error

💡 Hint

scanner.nextLine() reads the entire line including spaces.

The method scanner.nextLine() reads the whole line including spaces until the user presses Enter.

🔧 Debug

advanced

Why does this code skip input after reading an integer?

Look at this code snippet. The user inputs 5 and then Hello. Why does the program skip reading the string and print an empty line?

Java

import java.util.Scanner;

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

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

B nextLine() cannot read after nextInt() and causes an error

C The code has a syntax error and does not compile

D nextInt() consumes the whole line including the string

💡 Hint

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

nextInt() reads only the integer but leaves the newline character in the input buffer. Then nextLine() reads that leftover newline as an empty string.

📝 Syntax

advanced

Which option causes a compilation error when reading input?

Which of the following Java code snippets will cause a compilation error?

A

Scanner scanner = new Scanner(System.in);
String input = scanner.nextLine();
scanner.close();

B

;)(esolc.rennacs
;)(eniLtxen.rennacs = tupni gnirtS
;)ni.metsyS(rennacS wen = rennacs rennacS

C

Scanner scanner = new Scanner(System.in);
String input = scanner.next();
scanner.close();

D

Scanner scanner = new Scanner(System.in);
String input = scanner.readLine();
scanner.close();

💡 Hint

Check if the Scanner class has a method named readLine().

Scanner class does not have a method called readLine(). The correct method to read a line is nextLine().

🚀 Application

expert

How many strings are printed by this code?

This Java program reads three lines of input and prints them. How many lines will it print if the user inputs:
Line1
Line2
Line3

Java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        for (int i = 0; i < 3; i++) {
            String line = scanner.nextLine();
            if (line.isEmpty()) {
                break;
            }
            System.out.println(line);
        }
        scanner.close();
    }
}

A 3

B 2

C 0

D 1

💡 Hint

The loop runs 3 times and prints each non-empty line.

The loop reads and prints each line until 3 lines are read or an empty line is encountered. Since all inputs are non-empty, it prints all 3 lines.