Question

我正在开发这个项目，允许用户在输出窗口中输入名称，但是他们不能输入数字。我无法弄清楚正确的代码行，使其无法输入数字（如果他们这样做会给他们一个错误信息）。

import java.util.*;

public class UserInput 
{
public static void main(String[] args) 
{
    List<String> list = new ArrayList<String>();
  Scanner stdin = new Scanner(System.in);

  do 
    {   
     Collections.sort(list);
    System.out.println("Current list is " + list);
     System.out.println("Add more? (y/n)");

    if (stdin.next().startsWith("y")) 
        {
        System.out.println("Enter: ");
        list.add(stdin.next());
     } 

        else 
        {
        break;
     }
    } 

    while (true);

  System.out.println("List is " + list);
  String[] arr = list.toArray(new String[0]);
  System.out.println("Array is " + Arrays.toString(arr));
}
}
public void add(String string) {

try {  
   double d = Double.parseDouble(string);  
   } catch(NumberFormatException e) {  
       // throw a exception or something.
       return;
   }

   super.add(string);
   return;      
}

这是我的代码！

非常感谢您的帮助！

Answer 1

对输入进行正则表达式测试

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class UserInput {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        Scanner stdin = new Scanner(System.in);

        do {
            System.out.println("Enter: ");
            String strin = stdin.next();
            if (isNumeric(strin)) {
                System.out.println("Please enter a non numeric value");
            } else {
                list.add(strin);
            }

            Collections.sort(list);
            System.out.println("Current list is " + list);
            System.out.println("Add more? (y/n)");

        } while (stdin.next().startsWith("y"));

        System.out.println("List is " + list);
        String[] arr = list.toArray(new String[0]);
        System.out.println("Array is " + Arrays.toString(arr));
    }

    public static boolean isNumeric(String str) {
        return str.matches("-?\\d+(\\.\\d+)?");
    }
}

Answer 2

您可以创建一个扩展ArrayList并覆盖add()方法的类，检查给定的String是否为数字。

import java.util.*;

public class UserInput 
{
public static void main(String[] args) 
{
    List<String> list = new MyArrayList<String>();
  Scanner stdin = new Scanner(System.in);

  do 
    {   
     Collections.sort(list);
    System.out.println("Current list is " + list);
     System.out.println("Add more? (y/n)");

    if (stdin.next().startsWith("y")) 
        {
        System.out.println("Enter: ");
        try {

            list.add(stdin.next());
        } catch (Exception e) {
           // given string was a number.
        }
     } 

        else 
        {
        break;
     }
    } 

    while (true);

  System.out.println("List is " + list);
  String[] arr = list.toArray(new String[0]);
  System.out.println("Array is " + Arrays.toString(arr));
}
}
class MyArrayList extends ArrayList<String> {

    public void add(String string) {

       try {  
           double d = Double.parseDouble(string);  
       } catch(NumberFormatException e) {  
           super.add(string);
           return;
       }

       throw new Exception();
}

但您也需要覆盖其他“add”方法。

使Arraylist（）不允许输入数字EDITED

2 个答案: