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()
