在包含字符串和双精度的外部文本文件上使用扫描仪

Question

Making a java program to read a text file containing both string and doubles as a price list and storing them in a Hashmap. Keep on getting "java.util.InputMismatchException" errors in the nextDouble() line. Code:

    public static void main(String[] args) throws IOException {

        String priceList = "src/" + args[0];
        String cartOne = "src/" + args[1];
        String cartTwo = "src/" + args[2];
        Scanner priceScan = new Scanner(new File(priceList));
        priceScan.useDelimiter("    ");
        HashMap<String, Double> prices = new HashMap<String, Double>();
        priceScan.useDelimiter(" ");
        while (priceScan.hasNext()) {
            String name = priceScan.next();
            Double price = priceScan.nextDouble();
            prices.put(name, price);

        }
        priceScan.close();
        System.out.println(prices);
    }

the text file is as follows:

TV          999.99
Table         199 
Bed         499.99
Chair         45.49
Milk    3.00
Butter  2.84
Tomato 0.76
Onion 0.54
Lettuce 1.00
Ham 2.50
Bread 1.75

Answer 1

Your map was mapping strings to strings, when it should be mapping strings to doubles.

Scanner priceScan = new Scanner(new File(priceList));
HashMap<String, Double> prices = new HashMap<String, Double>();
while (priceScan.hasNext()) {
    String name = priceScan.next();
    Double price = priceScan.nextDouble();
    prices.put(name, price);
}
priceScan.close();

Answer 2

You are passing Double in place of String as argument. Error is obvious.

HashMap<String, String> prices = new HashMap<String, String>();

prices.put(name, price); //price is a Double

Answer 3

No need of calling useDelimiter() since scanner already uses spaces as delimiter to determine its tokens.

Also change the data type for HashMap's Value.

Here is the final program and a sample run:

import java.io.*;
import java.util.*;

class abcd
{
public static void main(String[] args) throws IOException {

        String priceList = "file";
        //String cartOne = "src/" + args[1];
        //String cartTwo = "src/" + args[2];
        Scanner priceScan = new Scanner(new File(priceList));
        HashMap<String, Double> prices = new HashMap<String, Double>();
        while (priceScan.hasNext()) {
            String name = priceScan.next();
            Double price = priceScan.nextDouble();
            prices.put(name, price);

        }
        priceScan.close();
        System.out.println(prices);
    }
}

Sample run:

$ cat file 
TV          999.99
Table         199 
Bed         499.99
Chair         45.49
Milk    3.00
Butter  2.84
Tomato 0.76
Onion 0.54
Lettuce 1.00
Ham 2.50
Bread 1.75
$ javac abcd.java 
$ java abcd 
{Bed=499.99, TV=999.99, Lettuce=1.0, Table=199.0, Chair=45.49, Onion=0.54, Ham=2.5, Butter=2.84, Tomato=0.76, Milk=3.0, Bread=1.75}