不允许用于基本输入计算的 try catch 块

Question

如果输入ENTER，即null或空字符串，会抛出如下错误。似乎无法解决它。

Exception in thread "main" java.lang.NumberFormatException: empty String at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842) at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.lang.Double.parseDouble(Double.java:538) at com.company.Main.main(Main.java:67) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

说明

Design a program that will prompt for and read in two numbers as strings. The numbers could be decimal numbers (double or float) or whole numbers (int). Convert these numbers from String to numeric. You can either choose the correct numeric type for the number of convert directly to double since it is the largest enclosing type. If the numbers are not valid, please inform the user and prompt again. After both valid numbers are read in, read in an operator (+, -, *, /). If the operator read in is not one of the allowed operators, inform the user and prompt again. Once everything is valid perform the indicated operation using the two numbers.

Do not use a try...catch block to intercept errors. All other options are open to you.

package com.company;

import java.util.Scanner;

    public class Main {

        public static void main(String[] args) {

            String sInput;
            String nInput;
            double dInput;

            String sInput2;
            String nInput2;
            double dInput2;

            boolean inputOK = false;
            String operator = "";

            int decCount;
            String operatorSelect;
            double total = 0;

            Scanner scanner = new Scanner(System.in);

            while (true) {
                do {
                    System.out.print("Enter first number: ");
                    //decimals count validation reset.
                    decCount = 0;
                    sInput = scanner.nextLine();
                    if (sInput == null) {
                        sInput = "0";
                    }
                    //purge !numerals || !decimals.
                    nInput = sInput.replaceAll("[^0-9.]", "");
                    //decimal count validation.
                    for (int i = 0; i < nInput.length(); i++) {
                        if (nInput.charAt(i) == '.') {
                            decCount = decCount + 1;
                        }
                    }
                    //break if input valid.
                    if (decCount <= 1) {
                        break;
                    }
                } while (true);
                dInput = Double.parseDouble(nInput);

                do {
                    System.out.print("Enter second number: ");
                    //decimals count validation reset.
                    decCount = 0;
                    sInput2 = scanner.nextLine();
                    //purge !numerals || !decimals.
                    nInput2 = sInput2.replaceAll("[^0-9.]", "");
                    //decimal count validation.
                    for (int i = 0; i < nInput2.length(); i++) {
                        if (nInput2.charAt(i) == '.') {
                            decCount = decCount + 1;
                        }
                    }
                    //break if input valid.
                    if (decCount <= 1) {
                        break;
                    }
                } while (true);
                dInput2 = Double.parseDouble(nInput2);
                while (inputOK == false) {
                    System.out.println("Operator to select: \n1) +\n2) -\n3) *\n4) /\n");
                    operatorSelect = scanner.nextLine();
                    switch (operatorSelect) {
                        case "1":
                            total = dInput + dInput2;
                            inputOK = true;
                            operator = "+";
                            break;
                        case "2":
                            total = dInput - dInput2;
                            inputOK = true;
                            operator = "-";
                            break;
                        case "3":
                            total = dInput * dInput2;
                            inputOK = true;
                            operator = "*";
                            break;
                        case "4":
                            total = dInput / dInput2;
                            inputOK = true;
                            operator = "/";
                            break;
                        default:
                            System.out.println("Invalid input.");
                    }
                }
                System.out.println(dInput + " " + operator + " " + dInput2 + " = " + total);
            }
        }
    }

Answer 1

如果按回车键，sInput 不为空，它是一个空字符串。

sInput = scanner.nextLine();
if (sInput.equals("")) {
  sInput = "0";
}

Answer 2

表达式 ^-?\d+(,\d+)*(\.\d+(e\d+)?)?$ 将匹配以可选的负号开头的字符串，一个或多个数字，可选地后跟一个逗号和更多数字，后跟一个可选的小数部分，它由一个句点组成，一个或多个数字，以及另一个可选组件，指数后跟更多数字。

这不是唯一的解决方案，因为可以有许多表达式可以匹配这些数字字符串集。

我没有优化你的代码只是添加了正则表达式检查和空检查

import java.util.Scanner;

    public class Main {

    public static void main(String[] args) {

        String sInput;
        String nInput;
        double dInput;

        String sInput2;
        String nInput2;
        double dInput2;

        boolean inputOK = false;
        String operator = "";

        int decCount;
        String operatorSelect;
        double total = 0;

        Scanner scanner = new Scanner(System.in);

        while (true) {
            do {
                System.out.print("Enter first number: ");
                //decimals count validation reset.
                decCount = 0;
                sInput = scanner.nextLine();
                if (sInput.isEmpty()) {
                    System.out.println("Empty value Please Enter again");
                    continue;
                }
                if (!sInput.matches("^-?\d+(,\d+)*(\.\d+(e\d+)?)?$")) {
                    System.out.println("Invalid input Please Enter again");
                    continue;
                }
                break;

                //Not needed regex will take care of everything
//                //purge !numerals || !decimals.
//                nInput = sInput.replaceAll("[^0-9.]", "");
//                //decimal count validation.
//                for (int i = 0; i < nInput.length(); i++) {
//                    if (nInput.charAt(i) == '.') {
//                        decCount = decCount + 1;
//                    }
//                }
//                //break if input valid.
//                if (decCount <= 1) {
//                    break;
//                }
            } while (true);
            dInput = Double.parseDouble(sInput);

            do {
                System.out.print("Enter second number: ");
                //decimals count validation reset.
                decCount = 0;
                sInput2 = scanner.nextLine();
                if (sInput2.isEmpty()) {
                    System.out.println("Empty value Please Enter again");
                    continue;
                }
                if (!sInput2.matches("^-?\d+(,\d+)*(\.\d+(e\d+)?)?$")) {
                    System.out.println("Invalid input Please Enter again");
                    continue;
                }
                break;
                //purge !numerals || !decimals.
//                nInput2 = sInput2.replaceAll("[^0-9.]", "");
//                //decimal count validation.
//                for (int i = 0; i < nInput2.length(); i++) {
//                    if (nInput2.charAt(i) == '.') {
//                        decCount = decCount + 1;
//                    }
//                }
//                //break if input valid.
//                if (decCount <= 1) {
//                    break;
//                }
            } while (true);
            dInput2 = Double.parseDouble(sInput2);
            while (inputOK == false) {
                System.out.println("Operator to select: \n1) +\n2) -\n3) *\n4) /\n");
                operatorSelect = scanner.nextLine();
                switch (operatorSelect) {
                    case "1":
                        total = dInput + dInput2;
                        inputOK = true;
                        operator = "+";
                        break;
                    case "2":
                        total = dInput - dInput2;
                        inputOK = true;
                        operator = "-";
                        break;
                    case "3":
                        total = dInput * dInput2;
                        inputOK = true;
                        operator = "*";
                        break;
                    case "4":
                        total = dInput / dInput2;
                        inputOK = true;
                        operator = "/";
                        break;
                    default:
                        System.out.println("Invalid input.");
                }
            }
            System.out.println(dInput + " " + operator + " " + dInput2 + " = " + total);
            break;
        }
    }
}

不允许用于基本输入计算的 try catch 块

Not allowed try catch block for basic input computation

java

try-catch