Java Scanner nextBoolean() Method

The nextBoolean() method in Java, part of the java.util.Scanner class, is used to retrieve the next token from the input as a boolean value. This method is useful for reading and processing boolean values from the input.

Table of Contents

1. Introduction
2. nextBoolean() Method Syntax
3. Understanding nextBoolean()
4. Examples
   • Basic Usage
   • Handling Input Errors
5. Real-World Use Case
6. Conclusion

Introduction

The nextBoolean() method returns the next token from the scanner's input as a boolean. It is useful when you need to read and process boolean values, typically represented as "true" or "false" in the input.

nextBoolean() Method Syntax

The syntax for the nextBoolean() method is as follows:

public boolean nextBoolean()

Parameters:

• This method does not take any parameters.

Returns:

• The next token as a boolean value.

Throws:

• InputMismatchException: If the next token does not match the boolean pattern.
• NoSuchElementException: If no more tokens are available.
• IllegalStateException: If the scanner is closed.

Understanding nextBoolean()

The nextBoolean() method retrieves the next token and converts it to a boolean. The token must match "true" or "false" (case insensitive). If the token cannot be interpreted as a boolean, an InputMismatchException is thrown.

Examples

Basic Usage

To demonstrate the basic usage of nextBoolean(), we will create a Scanner object and use it to read boolean values from a string.

Example

import java.util.Scanner;

public class NextBooleanExample {
    public static void main(String[] args) {
        String input = "true false TRUE FALSE";

        // Create Scanner object in try-with-resources to ensure it closes automatically
        try (Scanner scanner = new Scanner(input)) {

            while (scanner.hasNextBoolean()) {
                boolean value = scanner.nextBoolean();
                System.out.println("Boolean value: " + value);
            }
        } // Scanner is automatically closed here
    }
}

Output:

Boolean value: true
Boolean value: false
Boolean value: true
Boolean value: false

Handling Input Errors

This example shows how to handle errors when the input token cannot be interpreted as a boolean.

Example

import java.util.InputMismatchException;
import java.util.Scanner;

public class HandleInputErrorsExample {
    public static void main(String[] args) {
        String input = "true abc false";

        // Create Scanner object in try-with-resources to ensure it closes automatically
        try (Scanner scanner = new Scanner(input)) {

            while (scanner.hasNext()) {
                try {
                    boolean value = scanner.nextBoolean();
                    System.out.println("Boolean value: " + value);
                } catch (InputMismatchException e) {
                    System.out.println("Invalid input: " + scanner.next());
                }
            }
        } // Scanner is automatically closed here
    }
}

Output:

Boolean value: true
Invalid input: abc
Boolean value: false

Real-World Use Case

Reading Configuration Data

In real-world applications, the nextBoolean() method can be used to read and process boolean configuration data from a file.

Example

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ConfigParser {
    public static void main(String[] args) {
        try (Scanner scanner = new Scanner(new File("config.txt"))) {
            while (scanner.hasNext()) {
                try {
                    boolean value = scanner.nextBoolean();
                    System.out.println("Configuration value: " + value);
                } catch (InputMismatchException e) {
                    System.out.println("Invalid input: " + scanner.next());
                }
            }
        } catch (FileNotFoundException e) {
            System.out.println("File not found: " + e.getMessage());
        } // Scanner is automatically closed here
    }
}

Output (Assuming config.txt contains valid and invalid boolean values):

Configuration value: true
Invalid input: abc
Configuration value: false
...

Conclusion

The Scanner.nextBoolean() method is used to retrieve the next token from the input as a boolean value. This method is particularly useful for applications requiring boolean input values. By understanding and using this method, you can efficiently parse and handle boolean input data. Always close the Scanner using try-with-resources to ensure proper resource management.