Develop Reference

NoSuchElementException reffers to first scanner when another is created

so there is probably someone in the group who has similar problem but i couldn't find close one as mine. I cant make 2 scanners work, one after another... adding 2nd scanner makes 1st go nuts and throw
"NoSuchElementException"
at the start of the scanner command.
here is my code:
public class Stiklainiai {
static Scanner program = new Scanner(System.in);
static Scanner name_input = new Scanner(System.in);
public static void main(String[] argumentai){
System.out.println("Welcome to Java IDE !");
name();
jar();
}
public static String name() {
String name_select;
System.out.println("name yourself");
name_select = name_input.next();
name_input.close();
return name_select;
}
public static int jar(){
int jar_select; // input variable (1-6) for "if" statement
int jar_weight_assigned = 0; //unassigned capacity (applied by default if error occurs (outside 1-6 bounds))
String jar_name_assigned = ""; //unassigned name (applied by default if error occurs (outside 1-6 bounds))
int custom_jar_cap = 0; //custom "int" variable (custom jar)
String custom_jar_name = ""; //custom "String" variable (custom jar)
int[] jar_weight_arr = new int[5]; //jar capacity array
String[] jar_name_arr = new String[5]; //jar name array
jar_weight_arr[0] = 9;
jar_weight_arr[1] = 99;
jar_weight_arr[2] = 999;
jar_weight_arr[3] = 9999;
jar_weight_arr[4] = 99999;
jar_name_arr[0] = "bybiene22";
jar_name_arr[1] = "bybiene44";
jar_name_arr[2] = "bybiene66";
jar_name_arr[3] = "bybiene88";
jar_name_arr[4] = "bybiene000";
jar_select = program.nextInt();
...
...
...
and so on goes the rest of the code.
when i run it i can input a name but afterwards i get "NoSuchElementException" that refers to:
jar_select = program.nextInt(); (where the scanner opens)
followed by the declared method error in main method:
jar();
rest of the code works fine with just one scanner...
my point is to make one method with separate scanner that assigns name to the
"x" variable, and returns the value to main method. Then, the second runs the rest of the program in the other method, using the "x" variable with the value imputed
anyone knows the cause, i'm fairly fresh in java :)

The problem is hidden behind Scanner.close. Whenever you close the Scanner, you also close the underlying System.in, so it wont be available the text time your access it using your second scanner.
Solution: Do not close the first Scanner.

Java: how to reject incorrect input and wait for proper input using Scanner

This is the basic setup for a little console-based quiz game. The answers are numbered. I want the player to give the answer number. If the input is not a number, then my program should give a warning, and wait for proper input.
Instead, what I get (after inserting something that is not a number) is an infinite loop of asking the question and presenting the answers again.
public static void main(String[] args) {
boolean quizActive = true;
while(quizActive) {
presentQuestion();
presentAnswers();
Scanner s = new Scanner(System.in);
if (s.hasNext()) {
String choice = s.next();
if (!NumberUtils.isNumber(choice)) {
presentText("Please insert the answer number.");
} else {
System.out.println("You made a choice!");
checkAnswer(choice);
quizActive = false;
}
s.close();
}
}
}
What am I doing wrong here?

If you do not want to question and answers be presented each time move presentQuestion() and presentAnswers() outside the loop.
But main problem is that you closing Scanner.
Remove s.close(); and move Scanner s = new Scanner(System.in); outside of the loop.

I really don't get the point in using scanner for acquiring user input.
The scanner class is perfect to process structured input from a flat file with known structure like an CSV.
But user input need to deal with all the human imperfection. After all the only advantage you get is not needing to call Integer.parseInt() your yourself at the cost to deal with the not cleared input when scanne.nextInt() fails...
So why not using InputStreamReader aside with a loop suggested by others?

Here an Example :
public class Application {
public static void main(String [] args) {
System.out.println("Please insert the answer number. ");
while (true) {
try {
Scanner in = new Scanner(System.in);
int choice = in.nextInt();
System.out.println("You made a choice!");
checkAnswer(choice);
break;
} catch (Exception e) {
System.out.println("Invalid Number, Please insert the answer number ");
}
}
}
}

You started your Quiz in a loop which is regulated by your quizActive boolean. That means that your methods presentQuestion() and presentAnswers() get called every time the loop starts again.
If you don't input a number but a character for example, your program will run the presentText("Please insert the answer number.") and start the loop again. As it starts the loop again, it will call the methods presentQuestion() and presentAnswers().
To stop that, you can do another loop around the input-sequence. Also your Scanner s = new Scanner(System.in) should be outside the loop. And you shouldn't close your Scanner right after the first input and then open it again!
if you want a code example, please tell me :)

Java Scanner no line found, and then Scanner closed error?

I have Java code that asks for user input and then stores this data in a string variable. The below function is part of a class called 'number' and is called in the main function.
public static void setVal(int i){
Scanner readIn = new Scanner(System.in);
//while (readIn.hasNextLine()){
str = readIn.nextLine();
numCheck = false;
if (i == 1){
while (!numCheck){
if (str.contains(" ")){
System.out.println("Please input a single item.");
str = readIn.nextLine();
}
else if (!isNumeric(str)){
System.out.println("Please input a valid number.");
str = readIn.nextLine();
}
else {
numCheck = true;
value = Double.parseDouble(str);
readIn.close();
}
}
readIn.close();
}
else if (i == 2){
while (!numCheck){
if (str.contains(" ")){
System.out.println("Please input a single item.");
str = readIn.nextLine();
}
else if (!isNumeric(str)){
System.out.println("Please input a valid number.");
str = readIn.nextLine();
}
else {
numCheck = true;
secondV = Double.parseDouble(str);
readIn.close();
}
}
readIn.close();
}
else {
System.out.println("An error has occurred.");
}
// }
readIn.close();
}
Part of the main function looks like this:
number input = new number();
for (int i = 1; i <= 2; i++){
input.setVal(i);
System.out.println("Now please input a second value for computing with the first.");
input.setVal(i);
}
I use the same function twice but handing it a different argument to distinguish assignment of the input to a different variable but when it runs a second time it throws a no line found error.
Applying some other advice you can see commented out I have added a 'hasNextLine()' check to check if the line exists before executing the code but this ends up at a 'Scanner closed' error even though I invoke a new instance of Scanner every time the function runs. I have also closed the scanner appropriately to ensure minimisation of errors.
I have no idea what's going wrong as I can create a Scanner in the main function and call '.nextLine()' as many times as requried without an error but when called again through a class method, I receive these errors.
Any help is appreciated, thanks in advance.

Scanner.close() documentation states that
If this scanner has not yet been closed then if its underlying
readable also implements the Closeable interface then the readable's
close method will be invoked. If this scanner is already closed then
invoking this method will have no effect.
On closing scanner, you are also closing System.in input stream, so when you reopen the scanner it will not find any open input stream.
Refer : java.util.NoSuchElementException - Scanner reading user input
Better pass scanner object from outside method as argument and then close it in calling method only when you are done with it.
Just to point out, is your String object str Static?
If not then you can't use it in your static method. Better you remove the static from method declaration.

You have to close the scanner when everything is done.

You have closed the scanner inout stream readIn.close(); twice.
You are closing the stream before picking line by line from the file. So you have to close it once after all the instances that use readIn is finished.

How to make a ONE static scanner global variable without closing scan constantly and use it within methods and the main method?

I want to create a static scanner but i will like to put the try catch block around it so it can automatically close avoiding resources
leaks and or this exception:
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1585)
at softwareEngineer.UserApp1.main(UserApp1.java:82)
Essentially I only want to create one static scanner declaration and use it throughout the main program and includes the static methods, at this point my code will require to create separate scanner for each method and you are force "scan.close()". the code below will recieve a exception handling error due to multiple scanner that was open and did not closein the program.
I updated the code now i get null pointer exception
import java.util.Scanner;
public class UserApp1 {
static User currentCustomer = null; //single object
static Scanner scan;
//-------------------------------------------------------
// Create a list, then repeatedly print the menu and do what the
// user asks until they quit
//-------------------------------------------------------
public static void main(String[] args) {
scan = new Scanner(System.in);)//scanner to avoid resource leak
printMenu(); //print menu system from another function
String choice = scan.nextLine(); //reads an input
final String EXIT_now = "0";
final String BACK = "back";
while (!(choice.equalsIgnoreCase(EXIT_now))){
switch(choice) {
case 1: break;
case 2:
currentCustomer = loginInput();<---- errors happens here
if(currentCustomer != null){
System.out.println("You have successfully login");
}
break;
default:
System.out.println("Sorry, invalid choice");
break;
} //ends switch
printMenu(); //print menu system from another function
choice = scan.nextLine(); //reads an input
}//ends while
System.out.println("\t\t GoodBye!\n Thank you for trying our program.");
System.exit(0);
}//ends main
//----------------------------
// Print the user's choices
//----------------------------
public static void printMenu() {
System.out.println("\t\t The User Login System ");
System.out.println("\t\t ======================");
System.out.println("The Menu Options:");
System.out.println("1: Register an Account");
System.out.println("2: Login to your Account");
System.out.println("3: Reset Password");
System.out.println("0: Quit/Exit ");
System.out.println("Please enter your selection > ");
} //ends printMenu
public static User loginInput(){
System.out.print( "\nFollow the Prompts to Log-In to your Account \n ");
System.out.print( "\nPlease enter your userid : \n ");
String userid = scan.nextLine();// <---- errors happens here
System.out.print( "\nPlease enter your password: \n ");
String pass = scan.nextLine();
currentCustomer = AccountList.loginUser(userid, pass);
if (currentCustomer != null)
{
return currentCustomer;
}
return null;
}//ends loginInput
}//ends class*

You're using a try-with-resources, which will automatically close it when you finish the try block. Try setting it to a variable like so:
public class MyClass {
private static Scanner scan;
public static void main(String[] args) {
scan = new Scanner(System.in);
}
}
Avoid making multiple scanners with the System.in input as well, as they will consume the stream and then you have an entirely different problem.

Avoid using a static global Scanner at all, by passing the Scanner instance you want to work with to the relevant methods. Consider this simplified example:
public static void main(String[] args) {
try(Scanner in = new Scanner(System.in)) {
String choice = in.nextLine().trim();
if(choice.equals("1")) {
doOp1(in);
} else if(choice.equals("2")) {
doOp2(in);
} else {
System.err.println("Invalid choice. Goodbye.");
}
}
}
// Method takes an open, functioning Scanner as an argument, therefore
// it doesn't need to close it, or worry about where it came from, it
// simply uses it, does what it needs to do, and returns, trusting
// the caller to properly close the Scanner, since it opened it.
private void doOp1(Scanner in) {
System.out.print("What is your name? ");
String name = in.nextLine().trim();
System.out.print("What is your favorite color? ");
String color = in.nextLine().trim();
}
private void doOpt2(Scanner in) {
...
}
You want to compartmentalize your resources to ensure they are limited in scope and easy to close. Putting them in global state of any kind makes that very difficult. Instead, separate the opening and closing of the resource from the code using it. This sort of compartmentalization makes for much more maintainable, readable, and testable code.
For instance, by passing an already open Scanner to your core business logic functions, you can mock a real user's behavior and create a test to ensure your code remains stable, by constructing a Scanner that reads from a hard coded String, and passing that into your method, without needing to run the whole class and type in the behavior your testing manually again and again.

Problem in looping when using method in Java

I'm doing a simple program regarding methods.
But I have one problem. Everything is already working except when looping.
When I choose to loop again. The program skips on inputting the name. And proceeds directly to the year and section.
Here's the code:
public static void main(String[] args) {
do{
System.out.println("Input info:");
name=stringGetter("Name: ");
yearandsec=stringGetter("Year and section: ");
sex_code=charGetter("Sex code: " + "\n" + "[M]" + "\n" + "[F]:");
scode=intGetter("Scholarship code: ");
ccode=intGetter("Course code: ");
units=intGetter("Units: ");
fee_per_unit=doubleGetter("Fee per unit: ");
misc=doubleGetter("Miscellaneous: ");
display();
switches(scode, units, fee_per_unit, misc);
System.out.println("Another?");
dec=rew.nextInt();
}while(dec==1);
}
Here's the method getting the value for name together with the year and section:
public static String stringGetter(String ny){
String sget;
System.out.println(ny);
sget=rew.nextLine();
return sget;
}
I'm really annoyed with this problem, and I don't have any idea on how to fix this. Please help. thanks

Here is a simpler and more complete program that reproduces the error:
public static Scanner rew = new Scanner(System.in);
public static void main(String[] args) {
int dec;
do {
System.out.println("Input info:");
String name=stringGetter("Name: ");
String yearandsec=stringGetter("Year and section: ");
dec=rew.nextInt();
} while(dec==1);
}
public static String stringGetter(String ny){
System.out.println(ny);
return rew.nextLine();
}
The problem is that after calling nextInt() the call to nextLine() reads up to the new line after the int (giving a blank line), not up to the next new line.
If you change dec to a String and change dec=rew.nextInt(); to dec=rew.nextLine(); then it will work fine. Here is a complete example that you can copy and paste into a blank file to see that it works correctly:
import java.util.*;
public class Program
{
public static Scanner rew = new Scanner(System.in);
public static void main(String[] args) {
String dec;
do {
System.out.println("Input info:");
String name = stringGetter("Name: ");
String yearandsec = stringGetter("Year and section: ");
dec = stringGetter("Enter 1 to continue: ");
} while(dec.equals("1"));
}
public static String stringGetter(String ny){
System.out.println(ny);
return rew.nextLine();
}
}
You may also want to consider adding proper parsing and validation to your program. Currently your program will behave in an undesirable way if the user enters invalid data.

The line:
dec = rew.nextInt();
Is reading an int value from the input stream and is not processing the newline character, then when you come back to point where you get the name at which point a new line is still in the Reader's buffer and gets consumed by the stringGetter returning an empty value for name.
Change the line to do something like:
do {
//....
s = stringGetter("Another (y/n)? ");
} while ("y".equals(s));

Well you haven't told us what "rew" is, nor what rew.nextInt() does. Is it possible that rew.nextInt() is waiting for the user to hit return, but only actually consuming one character of the input - so that the next call to rew.nextLine() (for the name) just immediately takes the rest of that line? I suspect that's what's happening because you're using System.in - usually reading from System.in only gives any input when you hit return.
(It's possible that this is also only a problem on Windows - I wonder whether it consumes the "\r" from System.in as the delimiter, leaving "\n" still in the buffer. Not sure.)
To test this, try typing in "1 Jon" when you're being asked whether or not to continue - I think it will then use "Jon" as the next name.
Essentially, I think using Scanner.nextInt() is going to have issues when the next call is to Scanner.nextString(). You might be better off using a BufferedReader and calling readLine() repeatedly, then parsing the data yourself.