Scanner nextBoolean() method in Java with Examples

The nextBoolean() method of java.util.Scanner class scans the next token of the input as a Boolean. If the translation is successful, the scanner advances past the input that matched.

Syntax:

public boolean nextBoolean()

Parameters: The function does not accepts any parameter.

Return Value: This function returns the Boolean scanned from the input.

Exceptions: The function throws three exceptions as described below:

• InputMismatchException: if the next token is not a valid boolean
• NoSuchElementException: throws if input is exhausted
• IllegalStateException: throws if this scanner is closed

Below programs illustrate the above function:

Program 1:

// Java program to illustrate the
// nextBoolean() method of Scanner class in Java
// without parameter

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        String s = "Gfg true 9 + 6 = 12.0 false";

        // create a new scanner
        // with the specified String Object
        Scanner scanner = new Scanner(s);

        while (scanner.hasNext()) {

            // if the next is a Boolean,
            // print found and the Boolean
            if (scanner.hasNextBoolean()) {
                System.out.println("Found Boolean value :"
                                   + scanner.nextBoolean());
            }

            // if no Boolean is foucnd,
            // print "Not Found:" and the token
            else {
                System.out.println("Not found Boolean() value :"
                                   + scanner.next());
            }
        }
        scanner.close();
    }
}

Output:

Not found Boolean() value :Gfg
Found Boolean value :true
Not found Boolean() value :9
Not found Boolean() value :+
Not found Boolean() value :6
Not found Boolean() value :=
Not found Boolean() value :12.0
Found Boolean value :false

Program 2: To demonstrate InputMismatchException

// Java program to illustrate the
// nextBoolean() method of Scanner class in Java
// InputMismatchException

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            String s = "Gfg 9 + 6 = 12.0";

            // create a new scanner
            // with the specified String Object
            Scanner scanner = new Scanner(s);

            while (scanner.hasNext()) {

                // if the next is a Boolean
                // print found and the Boolean
                // since the value 60 is out of range
                // it throws an exception

                System.out.println("Next Boolean value :"
                                   + scanner.nextBoolean());
            }
            scanner.close();
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

Output:

Exception thrown: java.util.InputMismatchException

Program 3: To demonstrate NoSuchElementException

// Java program to illustrate the
// nextBoolean() method of Scanner class in Java
// NoSuchElementException

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            String s = "Gfg";

            // create a new scanner
            // with the specified String Object
            Scanner scanner = new Scanner(s);

            // Trying to get the next Boolean value
            // more times than the scanner
            // Hence it will throw exception
            for (int i = 0; i < 5; i++) {

                // if the next is a Boolean,
                // print found and the Boolean
                if (scanner.hasNextBoolean()) {
                    System.out.println("Found Boolean value :"
                                       + scanner.nextBoolean());
                }

                // if no Boolean is found,
                // print "Not Found:" and the token
                else {
                    System.out.println("Not found Boolean value :"
                                       + scanner.next());
                }
            }
            scanner.close();
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

Output:

Not found Boolean value :Gfg
Exception thrown: java.util.NoSuchElementException

Program 4: To demonstrate IllegalStateException

// Java program to illustrate the
// nextBoolean() method of Scanner class in Java
// IllegalStateException

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            String s = "Gfg 9 + 6 = 12.0";

            // create a new scanner
            // with the specified String Object
            Scanner scanner = new Scanner(s);

            // close the scanner
            scanner.close();
            System.out.println("Scanner Closed");

            System.out.println("Trying to get "
                               + "next Boolean value");

            while (scanner.hasNext()) {

                // if the next is a Boolean,
                // print found and the Boolean
                if (scanner.hasNextBoolean()) {
                    System.out.println("Found Boolean value :"
                                       + scanner.nextBoolean());
                }

                // if no Boolean is found,
                // print "Not Found:" and the token
                else {
                    System.out.println("Not found Boolean value :"
                                       + scanner.next());
                }
            }
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

Output:

Scanner Closed
Trying to get next Boolean value
Exception thrown: java.lang.IllegalStateException: Scanner closed

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#nextBoolean()