使用Scanner读取Float时发生Eclipse错误

Question

As part of a training exercise I'm coding a project to simulate a vending machine, and when I take in a float value Eclipse throws the following errors:

The error in question occurs in this block of code:

public void Restock() {
            boolean done = false;
            Float price;
            String quit, name;
            Scanner scan = new Scanner(System.in);
            scan.useLocale(Locale.US);
            scan.useDelimiter("\\n");

            while (!done) {
                System.out.println("Enter Item Name: ");
                name = scan.next();
                System.out.println("Enter Price (XX.XX): $");
                price = scan.nextFloat();
                item = new Items(name, price);
                stock.add(item);
                System.out.println("Quit? (Y/N): ");
                quit = scan.next();
                while (!quit.equalsIgnoreCase("y") && !quit.equalsIgnoreCase("n")) {
                    System.out.println("Invalid Entry. Quit? (Y/N): ");
                    quit = scan.next();
                }
                if (quit.equalsIgnoreCase("y")) {
                    done = true;
                } else if (quit.equalsIgnoreCase("n")) {
                    done = false;
                }
            }
            scan.close();
        }

I've tried running the code without the delimiter, adding an additional 'scan.nextLine();' statement above 'price = scan.nextFloat();' and in that case on the second pass through the loop it skipped asking for the name and went right to the price. Can somebody help me figure this out?

Answer 1

Your question does not provide a lot of information. However, here's my quickest attempt at recreating your code:

import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.Locale;
import java.util.Scanner;

public class RestockDemo {
    public ArrayList<Items> stock = new ArrayList<Items>();

    public static void main(String[] args) {
        RestockDemo restockDemo = new RestockDemo();
        restockDemo.restock();
    }

    public void restock() {
        boolean done = false;
        float price;
        String quit, name;
        Scanner scan = new Scanner(System.in);
        scan.useLocale(Locale.US);
        scan.useDelimiter("\\n");

        while (!done) {
            System.out.print("Enter Item Name: ");
            name = scan.next();
            System.out.print("Enter Price (XX.XX): $");
            price = scan.nextFloat();

            Items item = new Items(name, price);
            stock.add(item);
            System.out.println(stock.get(0).name);
            System.out.println(stock.get(0).price);

            System.out.print("Quit? (Y/N): ");
            quit = scan.next();
            while (!quit.equalsIgnoreCase("y") && !quit.equalsIgnoreCase("n")) {
                System.out.print("Invalid Entry. Quit? (Y/N): ");
                quit = scan.next();
            }
            if (quit.equalsIgnoreCase("y")) {
                done = true;
            } else if (quit.equalsIgnoreCase("n")) {
                done = false;
            }
        }
        scan.close();
    }

    class Items {
        public String name;
        public double price;
        Items(String name, double price) {
            this.name = name;
            this.price = price;
        }
    }
}

I tried Bakna's solution in Eclipse and it worked of course. Accepting a string instead and parsing it as a float is probably a nice quick fix.

Nevertheless, the weird thing I experienced when experimenting with your code was that when I ran the code above with the original scan.nextFloat implementation on NetBeans, it worked. On the other hand, a java.util.InputMismatchException occurs when I try the code in Eclipse.

Here are the different outputs:

NetBeans:

run:
Enter Item Name: Lilly Pulitzer Pearl Romper
Enter Price (XX.XX): $198.88
Lilly Pulitzer Pearl Romper
198.8800048828125
Quit? (Y/N): y
BUILD SUCCESSFUL (total time: 8 minutes 0 seconds)

Eclipse:

Enter Item Name: Lilly Pulitzer Pearl Romper
Enter Price (XX.XX): $198.89
Exception in thread "main" java.util.InputMismatchException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextFloat(Unknown Source)
    at RestockDemo.restock(RestockDemo.java:26)
    at RestockDemo.main(RestockDemo.java:11)

Frankly, I'm surprised to find that two different development environments can produce inconsistent results and I'm curious to find out why. I am assuming it has something to do the new line delimiter, but I'm not sure.

Answer 2

While your question skips over a lot of information on how the class and everything else works, a possible source of your errors is that you are using a Float to store your value, but using nextFloat() to get your value, which returns a float . Shouldn't be an issue, but you never know. Regardless, a solution you may try (which is how it always works for me) in that instance is to replace scan.nextFloat() with Float.valueOf(scan.next()) so you don't have to depend on finicky autoboxing at all.