需要帮助检查 Java 中 If/else 语句中的空格

Question

I am new to learning java and I'm doing a project for my online class and currently stuck on part of it.

Write a program that checks the properness of a given variable name. More specifically, your program should specify whether a user-entered variable name is:

• illegal (no spaces allowed, must begin with a letter)
• legal, but uses poor style (should only use letters or digits)
• good

You don't need to check for an uppercase letter for the first letter in the second word, third word, etc.

So my problem is that since having space in a variable name is illegal, I need to check the user's input for space, and if there is one it needs to print that it is illegal. I also need to check for special symbols (like $%#) and if it is anywhere but the first character, have it print that it is legal but improper.

I feel like this is super simple I just can't figure it out.

import java.util.Scanner;
public class IdentiferCheck
{
   public static void main (String[] args)
{
   Scanner in = new Scanner (System.in);
  
  String variableName = "";
  char ch = ' '; //temp holder
  
  //Get User Input
  System.out.println("This program checks the properness of a proposed Java variable name.");
  System.out.println("Please enter a variable name (q to quit):");
  variableName = in.nextLine();
  
  
  //Check if variable name is proper
  do
  {
     //Check if first char is lowercase
     ch = variableName.charAt(0);
     
     if (Character.isLetter(ch) && Character.isLowerCase(ch))
     {
     
        System.out.println("Good!");
     
     }
     
     else if (Character.isDigit(ch) && Character.isUpperCase(ch) && variableName.contains(" "))
     {
     
        System.out.println("Illegal!");
     
     }
     
     
     //Allow user to input another name or quit
     System.out.println("Enter another name or press q to quit: ");
     variableName = in.nextLine();
     
  } while (!variableName.equalsIgnoreCase("q"));
}

}

Answer 1

make sure to read the following documentation for your task. It's worth noting that the requirements don't actually match the real world requirements of Java variable names. However, the most difficult part of this task is the logic rather than the script. I've written an example script for you below:

Subsequent characters may be letters, digits, dollar signs, or underscore characters. https://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html

import java.util.Scanner;

public class identifierCheck
{
public static void main(String[] args) {
    
    String input = " ";
    System.out.printf("type q to exit...\n");

    while (input.charAt(0) != 'q' && input.length() == 1) // Note the length so that you can use q for starting variable names
    {
        input = requestLine();

        if (checkValid(input))
        {
            System.out.printf("%s is legal...\n", input);
        }
    }
}

public static String requestLine()
{
    Scanner cmd = new Scanner(System.in);
    System.out.printf("Enter a variable name > ");
    return cmd.nextLine();
}

public static boolean startsWithLetter(String input)
{
    if (123 > (int)input.toLowerCase().charAt(0) && (int)input.toLowerCase().charAt(0) > 60)
    {
        return true;
    }
    else
    {
        return false;
    }
}

public static boolean containsInvalid(String input)
{
    if ((input.indexOf('$') != -1 || input.indexOf('_') != -1) && input.indexOf(' ') == -1)
    {
        System.out.printf("Using $ and/or _ in variable names is poor style...\n");
    }
    if (input.indexOf(' ') != -1) // Has a space in the string
    {
        return true;
    }
    else
    {
        return false;
    }
}

public static boolean checkValid(String input)
{
    if (!startsWithLetter(input))
    {
        System.out.printf("%s is illegal, must start with a letter (note: $ and _ are 'valid' to start variable names)...\n", input);
        return false;
    }
    else if (containsInvalid(input))
    {
        System.out.printf("%s is illegal, it must not contain spaces...\n", input);
        return false;
    }
    else
    {
        return true;
    }
}
}

Good luck with your course! Java's an excellent language to learn.