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Closing a Scanner throws java.util.NoSuchElementException
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Closed 2 years ago.
I just can't read with scanner. I read a lot of other posts but i just cannot understand what in the world is wrong with this. I have tried with Buffer read but it gives error as well.
I just can't figure it out. What should i do?
This is the error:
Start : 1
Exit : 2
=> 1
Enter your name
=>
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.base/java.util.Scanner.nextLine(Scanner.java:1651)
at pcGame/pkg.GameLogic.characterCreation(GameLogic.java:28)
at pcGame/pkg.GameLogic.main(GameLogic.java:41)
This is the code:
package pkg;
import java.util.Scanner;
public final class GameLogic {
public void gameMenu() {
System.out.print("Start : 1\nExit : 2\n=> ");
int opt = 1;
Scanner input = new Scanner(System.in);
opt = input.nextInt();
switch(opt) {
case 1:
input.close();
return;
case 2:
System.exit(0);
}
input.close();
}
public void characterCreation() {
Scanner input = new Scanner(System.in);
System.out.println("Enter your name\n=> ");
String name = input.nextLine();
System.out.println("Enter your \n=> ");
String story = input.nextLine();
//Player.initialize("name", "story"); //Initializes Player
input.close();
}
public static void main(String[] args) {
GameLogic game = new GameLogic();
game.gameMenu();
game.characterCreation();
while(true) {
//Game Happens
break;
}
}
}
Just try to remove input.close(); statements
Related
I am getting a NoSuchElementException which is probably due to Scanner and I get it after I add a student and go back to the menu.
My main method:
import java.util.ArrayList;
import java.util.Scanner;
public class Main {
static ArrayList<Student> students = new ArrayList<>();
static Scanner scan = new Scanner(System.in);
static Student s = new Student();
public static void main(String[] args) {
menu();
}
public static void menu() {
System.out.println(" ***Students Manage***\n");
System.out.println("1 - Insert a student");
System.out.println("2 - Display students");
System.out.println("3 - Remove student\n");
option();
}
public static void option() {
int option;
do {
System.out.print("Choose an option: ");
option = scan.nextInt();
}while(option < 1 || option > 3);
switch(option) {
case 1:
s.addStudent();
students.add(s);
break;
case 2:
showAllStudents();
}
menu();
}
private static void showAllStudents() {
for(int i = 0; i < students.size(); i++) {
students.get(i).toString();
}
}
}
My Student method:
import java.time.LocalDate;
import java.util.Scanner;
public class Student {
String name;
int studentNumber;
static int count = 1;
int yearNumber;
public Student() {
}
public void addStudent() {
Scanner scan = new Scanner(System.in);
LocalDate year = LocalDate.now();
yearNumber = year.getYear();
studentNumber = count++;
studentNumber += yearNumber * 10000;
System.out.print("Enter the student name: ");
name = scan.nextLine();
if(name == null || name.trim().equals("") || !name.contains(" "))
{
do{
if(name.trim().equals("")){
System.out.print("Please enter a valid name.\nEnter your name: ");
} else if(!name.contains(" ")) {
System.out.print("You should write at least 2 names(name and surname).\nEnter your name: ");
}
name = scan.nextLine();
}while(name == null || name.trim().equals("") || !name.contains(" "));
}
scan.close();
System.out.println("The student "+name+" was added to the student list "
+ "and his/her student number is "+studentNumber);
}
#Override
public String toString(){
return name+" - "+studentNumber;
}
}
The error that I'm getting:
Exception in thread "main" java.util.NoSuchElementException
at java.base/java.util.Scanner.throwFor(Scanner.java:937)
at java.base/java.util.Scanner.next(Scanner.java:1594)
at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
at StudentSchool.Main.option(Main.java:29)
at StudentSchool.Main.menu(Main.java:21)
at StudentSchool.Main.option(Main.java:40)
at StudentSchool.Main.menu(Main.java:21)
at StudentSchool.Main.option(Main.java:40)
at StudentSchool.Main.menu(Main.java:21)
at StudentSchool.Main.main(Main.java:13)
You have two problems in how you're using Scanner. The first is that you are opening a second Scanner on System.in while you have one already open and reading from it. This produces strange results due to buffering. You should create and use only a single Scanner object that you never close. You can do this by passing the Scanner you create in your main() method into your addStudent() method so that it can use that same Scanner instead of creating and later closing a new one. So...
public void addStudent(Scanner scan) {
// Scanner scan = new Scanner(System.in);
....
// scan.close();
....
public static void option() {
....
s.addStudent(scan);
...
When you do this, a second problem will arise. When you mix calls to nextInt and nextLine on a Scanner object, you run into a problem where nextInt only reads the numeric digits from the input stream, but leaves the newline character produce by the user hitting Return. When you then call readLine, it reads that newline that's already on the input stream, so instead of waiting for your input, it reads an empty line as the next result. To avoid this problem, you should add an extra call to readLine right after you call readInt to consume this stray newline character. So...
System.out.print("Choose an option: ");
option = scan.nextInt();
scan.nextLine();
Making these two changes should cause your program to behave as you desire.
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I have a console application with a main method and some methods that I call from main. There, I want to ask the user for some input, for which I use the Scanner class.
Here's my problem:
I find there is no way to use Scanner when reading inputs from outside main without random exceptions or unexpected behaviour. I have tried two approaches:
Having a Scanner global variable in the class containing main. Then
I use this same Scanner in all functions in that same class.
In every function I need to ask for input, I declare a new Scanner
variable, use it, and close it before exiting the function.
1. makes Scanner try to read twice. I mean, I have a sc.readLine in a function and, when I exit that function, I have another sc.readLine in main. I input once and the two readLine lines get executed, the second one reading an empty String.
2. throws Exception (base class Exception) when I call any sc.readLine for a second time during the execution of the program.
I have also noticed that any other method other than readLine is going to read various items on the same line. For example, line "10 20 30 40" would execute 4 sc.nextInt calls.
TL;DR: how do you use Scanner in a console application?
One way:
import java.util.Scanner;
public class Main {
private Scanner scanner = new Scanner(System.in);
public Scanner getScanner() {
return scanner;
}
void fun1() {
Scanner in = getScanner();
System.out.print("Enter a string: ");
System.out.println("You entered: " + in.nextLine());
}
void fun2() {
Scanner in = getScanner();
System.out.print("Enter an integer: ");
int n = 0;
try {
n = Integer.parseInt(in.nextLine());
} catch (NumberFormatException e) {
e.printStackTrace();
}
System.out.println(n + " + 10 = " + (n + 10));
}
public static void main(String[] args) {
Main m = new Main();
m.fun1();
m.fun2();
}
}
A sample run:
Enter a string: Hello world!
You entered: Hello world!
Enter an integer: 25
25 + 10 = 35
Another way:
import java.util.Scanner;
public class Main {
static void fun1(Scanner in) {
System.out.print("Enter a string: ");
System.out.println("You entered: " + in.nextLine());
}
static void fun2(Scanner in) {
System.out.print("Enter an integer: ");
int n = 0;
try {
n = Integer.parseInt(in.nextLine());
} catch (NumberFormatException e) {
e.printStackTrace();
}
System.out.println(n + " + 10 = " + (n + 10));
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
fun1(in);
fun2(in);
}
}
A sample run:
Enter a string: Hello world!
You entered: Hello world!
Enter an integer: 25
25 + 10 = 35
Regarding your problem with next() or nextInt(): Given below is the recommended way for multiple inputs in one go.
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
boolean valid = true;
System.out.print("Enter some intgers: ");
String strNum = in.nextLine();
String[] strNumArr = strNum.split("\\s+");
int[] numArr = new int[strNumArr.length];
for (int i = 0; i < strNumArr.length; i++) {
try {
numArr[i] = Integer.parseInt(strNumArr[i]);
} catch (NumberFormatException e) {
numArr[i] = Integer.MIN_VALUE;
valid = false;
}
}
System.out.println(Arrays.toString(numArr));
if (!valid) {
System.out.println("Note: invalid inputs have been reset to " + Integer.MIN_VALUE);
}
}
}
A sample run:
Enter some intgers: 10 5 20 15
[10, 5, 20, 15]
Another sample run:
Enter some intgers: 4 40 a 20 b 15
[4, 40, -2147483648, 20, -2147483648, 15]
Note: invalid inputs have been reset to -2147483648
Check Scanner is skipping nextLine() after using next() or nextFoo()? for more information about console input using Scanner.
to use a single instance of Scanner (or any other datatype or class), you can use the design pattern "Singleton" which consist to instantiate a single instance of your Object for the whole project.
The Singleton definition (a new class) :
import java.util.Scanner;
public class ScannerSingleton {
private static Scanner sc = null;
private ScannerSingleton() {
sc = new Scanner(System.in);
}
public static Scanner getInstance() {
if (sc == null) {
synchronized(ScannerSingleton.class) {
if (sc == null)
sc = new ScannerSingleton();
}
}
}
}
and each time you want to use your scanner anywhere you only have to call ScannerSingleton.getInstance() which will return your single instance of scanner
example of use:
String test = ScannerSingleton.getInstance().nextLine();
I suggest to pass your Scanner object as another parameter for your functions.
public static void main(String[] args)
{
Scanner scanner=new Scanner(System.in);
String answer = ask(scanner, "what is your name?");
System.out.println("Oh! Hello dear " + answer + "!");
scanner.close();
}
private static String ask(Scanner scanner, String question)
{
System.out.println(question);
return scanner.nextLine();
}
Why do I get an exception error when trying to run this program? What does it mean and how can I fix it? Is it because I am using nextline? I get no error when running this in IntelliJ but when I run it in Zybooks (online coding lessons with assignments) I get the error.
My error:
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.base/java.util.Scanner.nextLine(Scanner.java:1651)
at ParseStrings.main(ParseStrings.java:40)
Code:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scnr = new Scanner(System.in);
String userInput = "";
System.out.println("Enter input string:");
userInput = scnr.nextLine();
while (!userInput.equals("q")) {
while (userInput.contains(",") == false) {
System.out.println("Error: No comma in string");
System.out.println("Enter input string:");
userInput = scnr.nextLine();
}
String[] myArray = userInput.split(",");
System.out.println("First word: " + myArray[0]);
System.out.println("Second word: " + myArray[1]);
//get the next input
System.out.println("Enter input string:");
userInput = scnr.nextLine();
}
}
}
The issue is when you assign a value to userInput variable so you aren't be able to call it again in loop while so you need call it from scanner, let me add this example:
while (!(userInput = scnr.nextLine()).equals("q")) {
....
}
I'm newbie in Java and I'm trying to read data from keyboard but I'm getting an exception and I don't know why and how to fix it.
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
Test r = new Test();
System.out.println("Type a int number : " + r.readInteger());
System.out.println("type a double number: " + r.readDouble());
}
public int readInteger() {
Scanner input = new Scanner(System.in);
int val = 0;
while(true) {
if(input.hasNextInt()) {
val = input.nextInt();
input.nextLine();
break;
}
else {
System.out.println("Invalid data type.");
input.nextLine();
}
}
input.close();
return val;
}
double readDouble() {
Scanner input = new Scanner(System.in);
double val = 0;
while(true) {
if(input.hasNextDouble()) {
val = input.nextDouble();
input.nextLine();
break;
}
else {
System.out.println("Invalid data type.");
input.nextLine();
}
}
input.close();
return val;
}
}
The excpetion:
[roger#archroger ~]$ java Test
3
Type a int number : 3
Invalid data type.
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1540)
at Test.readDouble(Test.java:44)
at Test.main(Test.java:8)
Don't close the scanner when it's input stream is System.in. This will close the standard input as well and statements like scanner.nextLine() will throw a NoSuchElementException when you do not check if the line is present. You check with scanner.hasNextInt() if another integer token is available and then try to get another line with scanner.getNextLine() without testing if this line exists at all. Use scanner.hasNextLine().
So I'm trying to use if-else statement dependant upon the user's input. It works when the user's input is only one word, however, multiple word inputs go unrecognized and triggers the else statement. How can i resolve this?
import java.util.Scanner;
public class MyFirstJavaClass {
public static void main(String[] args) {
#SuppressWarnings("resource")
Scanner myScanner = new Scanner(System.in);
String answer;
System.out.println("Catch the tiger or run away?");
answer = myScanner.next();
if (answer.equals("Catch the tiger" )) {
System.out.println("You've been mauled by a tiger! What were you thinking?");
answer = myScanner.next();
} else {
System.out.println("run away");
}
}
}
Replace:
answer = myScanner.next();
With:
answer = myScanner.nextLine();
next will only read in the next value until it reaches a space or newline. You want to read in the full line before making the comparison
try this :
Scanner scanner = new Scanner(System.in);
int choice = 0;
while (scanner.hasNext()){
if (scanner.hasNextInt()){
choice = scanner.nextInt();
break;
} else {
scanner.next(); // Just discard this, not interested...
}
}
Reference :
Flush/Clear System.in (stdin) before reading
Try this
import java.util.Scanner;
public class MyFirstJavaClass {
public static void main(String[] args) {
#SuppressWarnings("resource")
Scanner myScanner = new Scanner(System.in);
System.out.println("Catch the tiger or run away?");
if (myScanner.hasNext("Catch the tiger")) {
System.out.println("You've been mauled by a tiger! What were you thinking?");
} else {
System.out.println("run away");
}
}
}