當用戶輸入小數點時，如何錯誤處理代碼以防止程序崩潰？

Question

這是在Java中，我的問題是，當用戶輸入“ depositAmount”時，如果他們使用小數點或逗號，則程序會崩潰，我知道他們的輸入必須是double類型，但我不知道怎么說“如果用戶輸入的是雙精度，則接受它，否則，要求新的輸入”

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（）方法從Scanner接收最初沒有int或double值的輸入。 如果知道數據類型，則可以檢查它是否具有下一個雙精度型（hasNextDouble）或所需的任何數據類型。 如果不是，則可以接受String類型並將其轉換。

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

從那里，您可以將其解析為適當的數據類型（例如double）。

double d = Double.parseDouble(s);

希望對您有所幫助！

Answer 2

為此，您可以輕松地在Java中使用try / catch段。 如果用戶輸入的是整數而不是十進制，則程序將引發強制轉換異常，然后您可以根據需要進行處理（例如要求用戶再次輸入）。