java.util.NoSuchElementException - Scanner 读取用户输入

这真的让我困惑了一段时间，但这就是我最终发现的。

在第一种方法中调用时，它不仅会关闭扫描仪，还会关闭输入流。您可以通过在第二种方法的最顶部打印其状态来验证它，如下所示：sc.close()System.in

    System.out.println(System.in.available());

因此，现在当您在第二种方法中重新实例化时，它找不到任何打开的流，因此异常。ScannerSystem.in

我怀疑是否有任何出路可以重新开放，因为：System.in

public void close() throws IOException --> Closes this input stream and releases any system resources associated with this stream. The general contract of close is that it closes the input stream. A closed stream cannot perform input operations and **cannot be reopened.**

对于您的问题，唯一好的解决方案是启动 in main 方法，在两个方法中将其作为参数传递，然后在 main 方法中再次关闭它，例如：Scanner

main方法相关代码块：

Scanner scanner = new Scanner(System.in);  

// Ask users for quantities 
PromptCustomerQty(customer, ProductList, scanner );

// Ask user for payment method
PromptCustomerPayment(customer, scanner );

//close the scanner 
scanner.close();

您的方法：

 public static void PromptCustomerQty(Customer customer, 
                             ArrayList<Product> ProductList, Scanner scanner) {

    // no more scanner instantiation
    ...
    // no more scanner close
 }


 public static void PromptCustomerPayment (Customer customer, Scanner sc) {

    // no more scanner instantiation
    ...
    // no more scanner close
 }

希望这能让您对故障和可能的解决方法有所了解。

问题是

当扫描仪关闭时，如果源实现 Closeable 接口，它将关闭其输入源。

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Scanner.html

因此关闭 。scan.close()System.in

要修复它，您可以使

Scanner scan static并且不要在PromptCustomerQty中关闭它。下面的代码有效。

public static void main (String[] args) {   

// Create a customer
// Future proofing the possabiltiies of multiple customers
Customer customer = new Customer("Will");

// Create object for each Product
// (Name,Code,Description,Price)
// Initalize Qty at 0
Product Computer = new Product("Computer","PC1003","Basic Computer",399.99); 
Product Monitor = new Product("Monitor","MN1003","LCD Monitor",99.99);
Product Printer = new Product("Printer","PR1003x","Inkjet Printer",54.23);

// Define internal variables 
// ## DONT CHANGE 
ArrayList<Product> ProductList = new ArrayList<Product>(); // List to store Products
String formatString = "%-15s %-10s %-20s %-10s %-10s %n"; // Default format for output

// Add objects to list
ProductList.add(Computer);
ProductList.add(Monitor);
ProductList.add(Printer);

// Ask users for quantities 
PromptCustomerQty(customer, ProductList);

// Ask user for payment method
PromptCustomerPayment(customer);

// Create the header
PrintHeader(customer, formatString);

// Create Body
PrintBody(ProductList, formatString);   
}

static Scanner scan;

public static void PromptCustomerQty(Customer customer, ArrayList<Product> ProductList)               {
// Initiate a Scanner
scan = new Scanner(System.in);

// **** VARIABLES ****
int qty = 0;

// Greet Customer
System.out.println("Hello " + customer.getName());

// Loop through each item and ask for qty desired
for (Product p : ProductList) {

    do {
    // Ask user for qty
    System.out.println("How many would you like for product: " + p.name);
    System.out.print("> ");

    // Get input and set qty for the object
    qty = scan.nextInt();

    }
    while (qty < 0); // Validation

    p.setQty(qty); // Set qty for object
    qty = 0; // Reset count
}

// Cleanup

}

public static void PromptCustomerPayment (Customer customer) {
// Variables
String payment = "";

// Prompt User
do {
System.out.println("Would you like to pay in full? [Yes/No]");
System.out.print("> ");

payment = scan.next();

} while ((!payment.toLowerCase().equals("yes")) && (!payment.toLowerCase().equals("no")));

// Check/set result
if (payment.toLowerCase() == "yes") {
    customer.setPaidInFull(true);
}
else {
    customer.setPaidInFull(false);
}
}

顺便说一句，您不应该用于字符串比较，而应使用。==.equals