java - Java扫描器抛出了一些我未曾见过的错误

当我尝试运行我编写的这段代码时：

import java.util.Scanner;
    public class F1Calc
    {
        public static void main(String args[])
        {
            System.out.println("The coefficient of friction of the " + getSurface() + " surface is " + getCoeff() + ".  The mass of the ball was " + getMass() + " and the momentum of the ball was "+ getMomentum() + " Nm.  The potential energy contained by the ball at the top of the .121 m high ramp was " + getPotEnergy() + " Joules.");
        }
        public static String getSurface()
        {
            Scanner kb = new Scanner(System.in);
            System.out.println("What is the surface you are rolling the ball into?");
            String surface = kb.nextLine();
            kb.close();
            return surface;
        }
        public static double getMass()
        {
            Scanner kb2 = new Scanner(System.in);
            System.out.println("What is the mass of the ball in kilograms?");
            double mass = kb2.nextInt();
            kb2.close();
            return mass;
        }
        public static double getPotEnergy()
        {
            double potEnergy = getMass() * .121 * 9.8;
            return potEnergy;
        }
        public static double getMomentum()
        {
            double doublePE = 2 * getPotEnergy();
            double doublePEOverMass = doublePE / getMass();
            double velocity = Math.sqrt(doublePEOverMass);
            double momentum = velocity * getMass();
            return momentum;
        }
        public static double getCoeff()
        {
            double coeff = getPotEnergy() / (getMass() * 9.8);
            return coeff;
        }
    }

控制台上显示以下内容：

   What is the surface you are rolling the ball into?
    Tile
    What is the mass of the ball in kilograms?
    Exception in thread "main" java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Unknown Source)
        at java.util.Scanner.next(Unknown Source)
        at java.util.Scanner.nextInt(Unknown Source)
        at java.util.Scanner.nextInt(Unknown Source)
        at F1Calc.getMass(F1Calc.java:20)
        at F1Calc.getPotEnergy(F1Calc.java:26)
        at F1Calc.getCoeff(F1Calc.java:39)
        at F1Calc.main(F1Calc.java:6)

请指教。

最佳答案

扫描器仅使用一个基础InputStream，因此请不要关闭它-这样做会在以后的所有类实例中将其关闭，从而无法从源中读取