Encountering some bugs regarding the Scanner and an unknown source in my code. No idea how to fix it

问题

I'm trying to teach myself some java and this is my code, but these are the errors that i'm getting as soon as i make my first input telling the program which conversion mode to go into. Any help is appreciated

import java.util.Scanner;

public class TempConverter {

        public static void cToF(){
        double C=0, F=0, mode= 0;
        Scanner input = new Scanner(System.in);
        System.out.println("Enter your temperature in Celsius.");
        C = input.nextDouble();
        input.close();
        F = ((double)9/(double)5*C)+32;
        System.out.println("The temperature you entered in Celsius:"+ C);
        System.out.println("Converts to:"+ F + "in Fahrenheit");
        System.out.println("entery any number to switch converters");
        mode = input.nextDouble();
        if (mode< 0 || mode >0){

            ftoC();
        }
    }

    public static void ftoC(){
        double C=0, F=0, mode= 0;
        Scanner input = new Scanner(System.in);
        System.out.println("Enter your temperature in Fahrenheit.");
        F = input.nextDouble();
        input.close();
        C = (F-32)*((double)5/(double)9);
        System.out.println("The temperature you entered in Fahrenheit:"+ F);
        System.out.println("Converts to:"+ C + "in Celsius");
        System.out.println("entery any number to switch converters");
        mode = input.nextDouble();
        if (mode< 0 || mode >0){

            cToF();
    }
        }
    public static void main(String[] args) {
        int conv;
        System.out.println("Enter 1 for F to C conversion");
        System.out.println("Enter 2 for C to F conversion");
        Scanner input = new Scanner(System.in);
        conv = input.nextInt();
        input.close();
        if ( conv == 1) {

            cToF();
        }
        else {

            ftoC();
        }
    }
}

回答1:

The problem is with your input.close();. When Scanner is opened for System.in (keyboard entry stream), closing the Scanner also closes the stream itself.

Technical details:

System.in implements Closeable

From Scanner docs:

When a Scanner is closed, it will close its input source if the source implements the Closeable interface.

Suggested solution:

When using Scanner to capture keyboard input, open it once in the beginning and never close (or close at the very end of execution).

来源：https://stackoverflow.com/questions/27833107/encountering-some-bugs-regarding-the-scanner-and-an-unknown-source-in-my-code-n

标签

java

methods

java.util.scanner