java - 当我特别告诉它不要这样做时，程序仍然会收到信件

Question

至少在其中一行中。这是完整的代码。

import java.util.Scanner;

public class TestChar {

public static void main(String[] args) {

     Scanner input = new Scanner(System.in); 

        String myChar ;

        System.out.println(" Please input a character from your keyboard : ");
              myChar = input.nextLine();
              char c = myChar.charAt(0);
                 System.out.println(" You entered " + myChar);

                 System.out.println(" is it a letter? " + Character.isLetter(c));

                 System.out.println(" is it a number? " + Character.isDigit(c));        

                 System.out.println(" is it in lowercase? " + Character.isLowerCase(c));

                 System.out.println(" is it in uppercase? " + Character.isUpperCase(c));

                 if (Character.isLetter(c))
                           System.out.println(" In Upper Case : " + Character.toUpperCase(c) + ". And in lower case : " + Character.toLowerCase(c)) ;


               if 
                 (Character.isDigit(c) && !myChar.equals(Character.isLetter(c)))
                     System.out.println( myChar + " is a number.") ;                                           

              if  (!myChar.equals(Character.isLetter(c)) && !myChar.equals(Character.isDigit(c)))
                       System.out.println( myChar + " is neither a number nor letter.");

   }   

  }

我的另一项学校作业。最后一行代码选择了一个字母，当(我认为)我已经特别告诉它不是。我是编码方面的极端新手，所以请放轻松我的代码。

Answer 1

Character.isLetter() 和 Character.isDigit() 返回一个 boolean 值，您随后将其与 myChar 进行比较，后者是(有点误导)一个字符串。显然，它们永远不会相等。

这是一个正确且简化的版本:

if (Character.isLetter(c)) {
    System.out.println(" In Upper Case : " + Character.toUpperCase(c) + ". And in lower case : " + Character.toLowerCase(c));
} else if (Character.isDigit(c)) {
    System.out.println(c + " is a number.");
} else {
    System.out.println(c + " is neither a number nor letter.");
}