如何在用户输入特定关键词后停止从扫描器读取？

huangapple
go评论87阅读模式
英文:

How to stop reading from a scanner if the user inputs a specific keyword?

问题

我需要能够在控制台输入随机数量的整数，然后在完成时输入特殊字符比如Q。然而，我不确定如何验证输入是否为整数。

用户的目标是输入x个整数，然后将这些整数从客户端发送到服务器，服务器再通过一个简单的等式返回结果。我计划逐一发送这些整数，因为可以输入任意数量的整数。

我尝试过几种不同的方法。我尝试过使用hasNextInt方法。我尝试过使用nextLine，然后将每个输入添加到一个ArrayList，然后解析输入。

  1. List<String> list = new ArrayList<>();
  2. String line;
  4. while (!(line = scanner.nextLine()).equals("Q")) {
  5.     list.add(line);
  6. }
  8. list.forEach(s -> os.write(parseInt(s)));

这是我最初的另一个循环，它可以很好地验证输入，但是我不确定如何在完成时退出循环。

  1. while (x < 4) {
  2.     System.out.print("Enter a value: ");
  4.     while (!scanner.hasNextInt()) {    
  5.         System.out.print("Invalid input: Integer Required (Try again):");
  6.     }
  7.                
  8.     os.write(scanner.nextInt());
  9.     x++;
  10. }

任何帮助都将不胜感激。谢谢。

英文:

I need to be able to enter a random number of integers into the console and then enter a special character such as Q when I am finished. However, I am not sure how to validate if the input is an int or not.

The point is for the user to enter x amount of ints, which get sent from client to server and the server returns the result from a simple equation. I plan on sending them one at a time as it can be any amount of ints entered.

I have tried several different ways. I have tried using hasNextInt. I tried nextLine then added each input to an ArrayList then parsed the input.

  1. List&lt;String&gt; list = new ArrayList&lt;&gt;();
  2. String line;
  3.         
  4. while (!(line = scanner.nextLine()).equals(&quot;Q&quot;)) {
  5.     list.add(line);
  6. }
  7.         
  8. list.forEach(s -&gt; os.write(parseInt(s)));

This is another loop I had originally which validates the input fine, but i'm not sure how to exit the loop when done.

  1. while (x &lt; 4) {
  2.     System.out.print(&quot;Enter a value: &quot;);
  4.     while (!scanner.hasNextInt()) {    
  5.         System.out.print(&quot;Invalid input: Integer Required (Try again):&quot;);
  6.     }
  7.                
  8.     os.write(scanner.nextInt());
  9.     x++;
  10. }

Any help would be appreciated. Thanks

答案1

得分: 2

这里是代码翻译结果：

  1. 这是代码部分，已经翻译完成。
  3.     Scanner scanner = new Scanner(System.in);
  4.     List<Integer> list = new ArrayList<Integer>();
  5.     
  6.     while (scanner.hasNext()) {
  7.         String line = scanner.nextLine();
  8.     
  9.         if (line.equals("Q")) {
  10.             scanner.close();
  11.             break;
  12.         }
  13.     
  14.         try {
  15.             int val = Integer.parseInt(line);
  16.             list.add(val);
  17.         } catch (NumberFormatException e) {
  18.             System.err.println("请输入一个数字或者 Q 退出。");
  19.         }
  20.     }
英文:

Here you go:

  1. Scanner scanner = new Scanner(System.in);
  2. List&lt;Integer&gt; list = new ArrayList&lt;Integer&gt;();
  4. while (scanner.hasNext()) {
  5. 	String line = scanner.nextLine();
  7. 	if (line.equals(&quot;Q&quot;)) {
  8. 		scanner.close();
  9. 		break;
  10. 	}
  12. 	try {
  13. 		int val = Integer.parseInt(line);
  14. 		list.add(val);
  15. 	} catch (NumberFormatException e) {
  16. 		System.err.println(&quot;Please enter a number or Q to exit.&quot;);
  17. 	}
  18. }

答案2

得分: 2

按照以下方式执行：

  1. import java.util.ArrayList;
  2. import java.util.List;
  3. import java.util.Scanner;
  5. public class Main {
  7.     public static void main(String[] args) {
  8.         Scanner in = new Scanner(System.in);
  9.         List<Integer> list = new ArrayList<Integer>();
  10.         String input = "";
  11.         while (true) {
  12.             System.out.print("Enter an integer (Q to quit): ");
  13.             input = in.nextLine();
  14.             if (input.equalsIgnoreCase("Q")) {
  15.                 break;
  16.             }
  17.             if (!input.matches("\\d+")) {
  18.                 System.out.println("This is an invalid entry. Please try again");
  19.             } else {
  20.                 list.add(Integer.parseInt(input));
  21.             }
  22.         }
  23.         System.out.println(list);
  24.     }
  25. }

一个示例运行:

  1. Enter an integer (Q to quit): a
  2. This is an invalid entry. Please try again
  3. Enter an integer (Q to quit): 10
  4. Enter an integer (Q to quit): b
  5. This is an invalid entry. Please try again
  6. Enter an integer (Q to quit): 20
  7. Enter an integer (Q to quit): 10.5
  8. This is an invalid entry. Please try again
  9. Enter an integer (Q to quit): 30
  10. Enter an integer (Q to quit): q
  11. [10, 20, 30]

注:

  1. while(true) 创建一个无限循环。
  2. \\d+ 仅允许数字，即只允许整数。
  3. break 使循环中断。
英文:

Do it as follows:

  1. import java.util.ArrayList;
  2. import java.util.List;
  3. import java.util.Scanner;
  5. public class Main {
  7. 	public static void main(String[] args) {
  8. 		Scanner in = new Scanner(System.in);
  9. 		List&lt;Integer&gt; list = new ArrayList&lt;Integer&gt;();
  10. 		String input = &quot;&quot;;
  11. 		while (true) {
  12. 			System.out.print(&quot;Enter an integer (Q to quit): &quot;);
  13. 			input = in.nextLine();
  14. 			if (input.equalsIgnoreCase(&quot;Q&quot;)) {
  15. 				break;
  16. 			}
  17. 			if (!input.matches(&quot;\\d+&quot;)) {
  18. 				System.out.println(&quot;This is an invalid entry. Please try again&quot;);
  19. 			} else {
  20. 				list.add(Integer.parseInt(input));
  21. 			}
  22. 		}
  23. 		System.out.println(list);
  24. 	}
  25. }

A sample run:

  1. Enter an integer (Q to quit): a
  2. This is an invalid entry. Please try again
  3. Enter an integer (Q to quit): 10
  4. Enter an integer (Q to quit): b
  5. This is an invalid entry. Please try again
  6. Enter an integer (Q to quit): 20
  7. Enter an integer (Q to quit): 10.5
  8. This is an invalid entry. Please try again
  9. Enter an integer (Q to quit): 30
  10. Enter an integer (Q to quit): q
  11. [10, 20, 30]

Notes:

  1. while(true) creates an infinite loop.
  2. \\d+ allows only digits i.e. only an integer number.
  3. break causes the loop to break.

huangapple
  • 本文由 发表于 2020年4月8日 01:30:05
  • 转载请务必保留本文链接：https://go.coder-hub.com/61085897.html
  • java
  • java.util.scanner
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