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()
