Java 编码帮助！无法使 if 语句确认字符串

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英文:

Java Coding Help! Can't get if statement to confirm string

问题

  1. import java.util.*;
  3. public class MessAround {
  5.     public static void main(String[] args) {
  6.         Scanner scan = new Scanner(System.in);
  8.         System.out.println("请输入字母表中的单个字符：");
  9.         String letter = scan.next();
  11.         if (letter.length() == 1 && Character.isLetter(letter.charAt(0))) {
  12.             letter = letter.toLowerCase();
  13.             if (letter.equals("a") || letter.equals("e") || letter.equals("i") || letter.equals("o") || letter.equals("u")) {
  14.                 System.out.println("元音");
  15.             } else {
  16.                 System.out.println("辅音");
  17.             }
  18.         } else {
  19.             System.out.println("错误");
  20.         }
  21.     }
  22. }
英文:

Write a program that prompts the user to provide a single character from the alphabet. Print Vowel or Consonant, depending on the user input. If the user input is not a letter (between a and z or A and Z), or is a string of length > 1, print an error message.

I have been trying to solve this problem, and basically have it all figured out but have ran into two issues. How do I get the scanner to recognize an error if the user inputs a number rather than a letter. Also how would one not have to repeat their input. Is there a way to have the first if statement evaluate if the user entered a string?

  1. import java.util.*;
  3. public class MessAround {
  5. 	public static void main(String[] args) {
  6. 		Scanner scan = new Scanner(System.in);
  7. 		
  8. 		System.out.println("Please Provide single character from the alphabet: ");
  9.         String letter = scan.next();
  10.         
  11.         if (scan.hasNext())
  12.         {
  13.             letter = letter.toLowerCase();
  14.             if (letter.equals("a") || letter.equals("e") || letter.equals("i") || letter.equals("o") || letter.equals("u"))
  15.             {
  16.                 System.out.println("Vowel");
  17.             }
  18.             else if (letter.length() > 1)
  19.             {
  20.                 System.out.println("Error");
  21.             }
  22.             else
  23.             {
  24.                 System.out.println("Consonant");
  25.             }
  26.         }
  27.         else
  28.         {
  29.             System.out.println("Error");
  30.         }
  31. 	}
  33. }

答案1

得分: 0

将以下内容添加到您的if语句中：if (isNumber(letter)) { // 输入了一个数字。 并创建一个名为 isNumber(String) 的方法，如果字符串在您所指的意义上是一个数字，则返回 true。

或者更好地将其制作成一个名为 String isValid(String) 的方法，并在方法中实现您的验证规则。如果验证成功，它可以返回 null，否则返回一条消息。

英文:

Add to your ifs: if (isNumber(letter)) { // A number was entered. and create a isNumber(String) method that returns true if the string is a number in the sense that you mean it.

Or better make it a String isValid(String) method and implement in the method your validation rules. It could return null if the validation is successful otherwise a message.

答案2

得分: 0

使用正则表达式：

  1. import java.util.Scanner;
  3. public class Main {
  4.     public static void main(String[] args) {
  5.         Scanner scan = new Scanner(System.in);
  7.         System.out.print("请输入字母表中的单个字符：");
  8.         String letter = scan.next();
  10.         if (!letter.matches("[A-Za-z]")) {
  11.             System.out.println("错误");
  12.         } else {
  13.             letter = letter.toLowerCase();
  14.             if (letter.matches("[aeiou]")) {
  15.                 System.out.println("元音");
  16.             } else {
  17.                 System.out.println("辅音");
  18.             }
  19.         }
  20.     }
  21. }

从这里了解有关正则表达式的内容。

使用Character类：

  1. import java.util.Scanner;
  3. public class Main {
  4.     public static void main(String[] args) {
  5.         Scanner scan = new Scanner(System.in);
  7.         System.out.print("请输入字母表中的单个字符：");
  8.         String letter = scan.next();
  10.         if (letter.length() == 1 && Character.isAlphabetic(letter.charAt(0))) {
  11.             char ch = Character.toLowerCase(letter.charAt(0));
  12.             if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
  13.                 System.out.println("元音");
  14.             } else {
  15.                 System.out.println("辅音");
  16.             }
  17.         } else {
  18.             System.out.println("错误");
  19.         }
  20.     }
  21. }

这里了解有关Character类的信息。

英文:

There are many ways to solve this. A couple of them are as follows:

Using Regex:

  1. import java.util.Scanner;
  3. public class Main {
  4. 	public static void main(String[] args) {
  5. 		Scanner scan = new Scanner(System.in);
  7. 		System.out.print("Please Provide single character from the alphabet: ");
  8. 		String letter = scan.next();
  10. 		if (!letter.matches("[A-Za-z]")) {
  11. 			System.out.println("Error");
  12. 		} else {
  13. 			letter = letter.toLowerCase();
  14. 			if (letter.matches("[aeiou]")) {
  15. 				System.out.println("Vowel");
  16. 			} else {
  17. 				System.out.println("Consonant");
  18. 			}
  19. 		}
  20. 	}
  21. }

Learn about regex from here.

Using the class, Character:

  1. import java.util.Scanner;
  3. public class Main {
  4. 	public static void main(String[] args) {
  5. 		Scanner scan = new Scanner(System.in);
  7. 		System.out.print("Please Provide single character from the alphabet: ");
  8. 		String letter = scan.next();
  10. 		if (letter.length() == 1 && Character.isAlphabetic(letter.charAt(0))) {
  11. 			char ch = Character.toLowerCase(letter.charAt(0));
  12. 			if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
  13. 				System.out.println("Vowel");
  14. 			} else {
  15. 				System.out.println("Consonant");
  16. 			}
  17. 		} else {
  18. 			System.out.println("Error");
  19. 		}
  20. 	}
  21. }

huangapple
  • 本文由 发表于 2020年9月30日 02:32:54
  • 转载请务必保留本文链接：https://go.coder-hub.com/64125606.html
  • if-statement
  • java
  • java.util.scanner
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