How to Resolve java.util.NoSuchElementException When Using Scanner for User Input in Java

What causes java.util.NoSuchElementException when reading from Scanner in Java?

payment = sc.next(); // Code that causes the exception

The java.util.NoSuchElementException occurs when a Scanner object tries to read input but there isn't any available, often due to the Scanner being closed prematurely or trying to use multiple Scanner instances on the same input stream (like System.in). In your case, this happens because the Scanner used in the PromptCustomerQty method is closed, preventing the next Scanner instance in PromptCustomerPayment from accessing the input stream.

// Example: Use a single Scanner instance 
Scanner sc = new Scanner(System.in); 
PromptCustomerQty(customer, ProductList, sc); 
PromptCustomerPayment(customer, sc); 

// Modify PromptCustomerQty and PromptCustomerPayment to accept Scanner as a parameter 
public static void PromptCustomerQty(Customer customer, ArrayList<Product> ProductList, Scanner scan) { /* ... */ }
public static void PromptCustomerPayment(Customer customer, Scanner sc) { /* ... */ }

Causes

• Closing a Scanner that reads System.in prevents any subsequent Scanner from reading from the same input stream.
• Using multiple Scanner objects on System.in can lead to unexpected behavior and exceptions.

Solutions

• Do not close the Scanner that reads from System.in, as it will close the input stream entirely. Close it only in the main method after all input has been gathered.
• Use a single Scanner instance throughout your application to read input from the console.

Mistake: Closing the Scanner that reads from System.in

Solution: Avoid closing the Scanner to ensure the input stream remains open for subsequent reads.

Mistake: Creating multiple Scanner instances for System.in

Solution: Reuse the same Scanner instance for reading to prevent unexpected exceptions.