扫描仪上的数字类型

Question

我制作了一个简单的程序，根据公式中的3个数字计算增量。但是，小数点后的分数和数字（如3.33、3/4）有问题。如果我将其替换为任何字母，则会出现错误：

线程“main”java中出现异常。util。java上的InputMismatchException。base/java。util。扫描仪。throwFor（Scanner.java:939）访问java。base/java。util。扫描仪。下一步（Scanner.java:1594）是java。base/java。util。扫描仪。java上的nextInt（Scanner.java:2258）。base/java。util。扫描仪。位于Main的nextInt（Scanner.java:2212）。main（main.java:11）

如何添加修补程序以使程序正常工作？我的代码如下：

import java.util.Scanner;
import java.lang.Math;
import java.util.Locale;
public class Main {
    public static void main(String[] args) {
        final double n1; //a
        final double n2; //b
        final double n3; //c
        Scanner reader= new Scanner(System.in).useLocale(Locale.US);
        System.out.print("calculation of the delta. Enter the first number (a from the formula)");
        n1 = reader.nextDouble();
        System.out.print("give the second number (b from the formula)");
        n2 = reader.nextDouble();
        System.out.print("give the last number (c from the formula)");
        n3 = reader.nextDouble();
        final double delta = Math.pow(n2, 2) - 4 * n1 * n3;
        final double d01 = (-n2 + Math.sqrt(delta)) / (2 * n1);
        final double d02 = (-n2 - Math.sqrt(delta)) / (2 * n1);
        final String dinfo = "Delta is equal: ";
        if(delta>0) {
            System.out.println(dinfo + (int)delta + " , has [two] zero places, which is equal to: " + (int)d01 + " and " + (int)d02);
        }
        else if (delta == 0) {
            System.out.println(dinfo + (int)delta + ", has exactly [one] zero place, which is equal to: " + (int)d01);
        }
        else {
            System.out.println(dinfo + (int)delta + ", no zero places.");
        }
    }
}

Answer 1

先把int改成双

 final double n1; //a
 final double n2; //b
 final double n3; //c

 n1 = reader.nextDouble();
 n2 = reader.nextDouble();
 n3 = reader.nextDouble();

您需要设置区域设置。我们需要解决这个输入不匹配异常。否则，它可能会使用“，”或其他字符作为十进制分隔符。这将解决您的十进制问题

Scanner reader= new Scanner(System.in).useLocale(Locale.US);

Answer 2

如果要将输入数字接受为十进制，则应使用浮点或双精度类型。例如

double n1;
n1 = reader.nextDouble();

关于分数，您应该使用字符串类型，然后将其转换为数字类型。例如

    String tmp;
    Scanner reader= new Scanner(System.in).useLocale(Locale.US);
    System.out.print("calculation of the delta. Enter the first number (a from the formula)");
    tmp = reader.next();
    n1 = fractionToDouble(tmp);
    tmp = reader.next();
    n2 = fractionToDouble(tmp);
....

添加fractionToDouble转换方法。参考：米沙多夫的回答

static double fractionToDouble(String ratio) {
        if (ratio.contains("/")) {
            String[] rat = ratio.split("/");
            return Double.parseDouble(rat[0]) / Double.parseDouble(rat[1]);
        } else {
            return Double.parseDouble(ratio);
        }
    }