java - 如何在java中使用扫描仪处理奇怪的输入

Question

这个问题已经有答案了:

How to use java.util.Scanner to correctly read user input from System.in and act on it? (1 个回答)

已关闭 3 年前。

我正在编写代码，其中我正在制作一个应用程序，通过询问用户关于他或她想要执行的操作(例如查询、存储、添加联系人等)的特定选择来存储联系人。

下面是我的代码的子部分，我实际上是在尝试在用户输入错误的选择时解决问题。我的意思是，如果用户输入非数字字符，它应该再次要求选择，

package com.vakhariaKathan;
import java.util.Scanner;

public class Main
{
    private static Scanner scanner = new Scanner(System.in);
    private static MobilePhone mobilePhone = new MobilePhone();
    public static void main(String[] args)
    {
        int choice;
        boolean quit = false;
        System.out.println("Hey there! :),\nI am your Mobile Phone,📳");
        printInstructions();
        while(!quit)
        {
            System.out.print("Enter choice: ");
            if(!scanner.hasNextInt())
            {
                System.out.println("You entered something bad 😣");
                scanner.nextLine();
                continue;
            }
            choice = scanner.nextInt();scanner.nextLine();
            switch (choice)
            {
                case 0:
                    printInstructions();
                    break;
                case 1:
                    mobilePhone.printContacts();
                    break;
                case 2:
                    handleAdditionOfContact();
                    break;
                case 3:
                    System.out.print("Enter contact name to be changed: ");
                    mobilePhone.modifyContact(scanner.nextLine());
                    break;
                case 4:
                    System.out.println("Enter any name of the following you want to delete.");
                    mobilePhone.showContactNames();
                    mobilePhone.removeContact(scanner.nextLine());
                    break;
                case 5:
                    quit = true;
                    break;
                default:
                    System.out.println("Enter a valid choice!");
                    break;
            }

        }

    }

    private static void printInstructions()
    {
        System.out.println("Currently i can do following operations.");
        System.out.println("0.Print instructions.");
        System.out.println("1.Show list of contacts.");
        System.out.println("2.Add Contact.");
        System.out.println("3.Modify a contact.");
        System.out.println("4.Delete Contact.");
        System.out.println("5.Quit");
    }

    //to handle addition of contact
    private static void handleAdditionOfContact()
    {
        String[] output = takeInput();
        mobilePhone.addContact(output[0],output[1]);
    }

    //Method to take user input
    private static String[] takeInput()
    {
        String name,contact;
        System.out.print("Enter name of the Contact: ");
        name = handleEmptyEntry("Name");
        if(mobilePhone.doesExist(name))
        {
            System.out.println("That contact already exists.\nTry a different name");
            name = handleEmptyEntry("Name");
        }
        System.out.print("Enter contact number for " + name + ": ");
        contact = handleEmptyEntry("contact");
        return new String[] {name,contact};
    }
    //function to handle empty entry
    private static String handleEmptyEntry(String fieldName)
    {
        String in = scanner.nextLine();
        while (in.isBlank())
        {
            System.out.printf("%s field cannot be empty ‼\nEnter again:",fieldName);
            in = scanner.nextLine();

        }
        return in;
    }

}

主要有两种场景:

1)如果用户在没有按回车键的情况下输入了错误的字符，它也可以正常工作。2)但是当用户输入新行然后输入错误的字符时，它会表现出一些奇怪的行为。以下是显示这两种情况的输出。

Hey there! :),
I am your Mobile Phone,📳
Currently i can do following operations.
0.Print instructions.
1.Show list of contacts.
2.Add Contact.
3.Modify a contact.
4.Delete Contact.
5.Quit
Enter choice: p
You entered something bad 😣
Enter choice: 

i
You entered something bad 😣
Enter choice: You entered something bad 😣
Enter choice: You entered something bad 😣
Enter choice: 

很高兴能得到详细的解释!

Answer 1

如果您编写了 scanner.next() 那么您就不会遇到此问题，但是当您编写 scanner.nextLine() 时您会遇到此行为，因为之前输入非数字值 您按两次 Enter 键，然后输入非数字值。所以你得到了 3 次你输入了错误的内容。两次用于您按下的输入，一次用于非数字值。发生这种情况是因为换行符保留在缓冲区中，当您输入非数字值时，它会读取所有这些值并打印 您输入了错误的内容。

因此，如果您按 Enter 键 5 次，然后输入非数字值，您将得到 You Entered Something bad 6 times 打印结果。