当用户输入小数点时，我如何错误处理我的代码以防止程序崩溃

Question

这是在java中，我的问题是，当用户输入"depositAmount"时，如果他们使用小数点或逗号，程序就会崩溃，我知道他们的输入需要是double类型，但我不知道如何说"如果用户的输入是double，接受它，否则，请求新的输入"

import java.util.Scanner;
import java.util.ArrayList;
public class Engine
{
private static ArrayList<BankAccount> accounts = new ArrayList<BankAccount>();
public static void Engine()
{
    Scanner Reader = new Scanner(System.in);
    BankAccount n = new BankAccount();
    boolean keepGoing = true;
    while(keepGoing)
    {
        System.out.println("Welcome to The Bank of Money, what would you like to do?n enter n to create a new account, enter e to use an existing account, or enter q to quit to main menu");
        String response = Reader.nextLine();
        if(response.equals("q")) keepGoing = false;
        else if(response.equals("n")) 
        {
            accounts.add(new BankAccount());
            System.out.println("Your account number is: " + accounts.get(accounts.size()-1).getAccountNum());
        }
        else if(response.equals("e"))
        {
            System.out.println("what is your account number?");
            Scanner Reader1 = new Scanner (System.in);
            int accountNum = Reader1.nextInt();  
            BankAccount selectedAccount = null;
            for(int i = 0; i<accounts.size();i++)
            {
                if (accounts.get(i).getAccountNum()==accountNum)
                {
                    selectedAccount = accounts.get(i);
                }
            }
            if(selectedAccount ==null)System.out.println("There is no such account. Please try again.");
            else transact(selectedAccount);
        }
    }
}
public static void transact(BankAccount selectedAccount)
{
    Scanner in = new Scanner(System.in);
    int response = 0;
    while(response!=7)
    {
        BankAccount.printTransactionMenu();
        response = in.nextInt();
        if(response==1)
        {
            System.out.println("Enter the amount that you would like to deposit");
            System.out.print("$");
            Scanner depositScanner = new Scanner(System.in);
            double depositAmount = depositScanner.nextInt();
        }
        if(response==2)
        {
            System.out.println("Enter the amount that you would like to withdraw");
            System.out.print("$");
            Scanner withdrawScanner = new Scanner(System.in);
            double withdrawAmount = withdrawScanner.nextInt();
            if(withdrawAmount>selectedAccount.getBalance()) 
                System.out.println("Insufficient funds");
            else selectedAccount.withdraw(withdrawAmount);
        }
        if(response==3)
        {
            selectedAccount.assessInterest();
            System.out.println("Your new balance is $" + selectedAccount.getBalance());
        }
        if(response==4)
        {
            System.out.println("Your account balance is $" + selectedAccount.getBalance());
        }
        if(response==5)
        {
            System.out.println("Which account would you like to transact with?");
            Scanner Reader1 = new Scanner (System.in);
            int transactAccountNum = Reader1.nextInt();  
            BankAccount transactAccount = null;
            for(int i = 0; i<accounts.size();i++)
            {
                if (accounts.get(i).getAccountNum()==transactAccountNum)
                {
                    transactAccount = accounts.get(i);
                }
            }
            if(transactAccount ==null)System.out.println("There is no such account. Please try again.");
            else 
            {   
                System.out.println("What amount would you like to transfer?");
                Scanner transferScanner = new Scanner(System.in);
                double transactAmount = transferScanner.nextDouble();
                selectedAccount.transfer(transactAccount, transactAmount);
            }
        }
        if(response==6)
        {
            selectedAccount.printStatement();
        }
    }
}

}

Answer 1

您可以使用next（）方法从Scanner接收最初没有int或double值的输入。如果你知道数据类型，你可以检查它是否有下一个double（hasNextDouble）或你需要的任何数据类型。如果没有，你可以接受一个字符串类型并转换它

Scanner in = new Scanner(System.in);
String s = in.next();

从那里，您可以将其解析为适当的数据类型（例如double）。

double d = Double.parseDouble(s);

我希望这能有所帮助！

Answer 2

您可以很容易地在java中使用try/catch段来实现此目的。如果用户输入的是整数而不是十进制，程序将引发Cast异常，然后您可以根据自己的意愿进行处理（比如要求用户再次输入）。