为多个异常创建捕获块

Question

I'm trying to write this program that is made up of three classes with an exception in each class - using inheritance. Inside of our tester class we are suppose to use a catch block and i'm having trouble understanding the idea.

The program outcome is as follows:

• If the sentence ends in anything except a period (.), exclamation point (!), or question mark (?), the program should throw a PunctuationException.
• If the sentence specifically ends in a comma, the program should throw a CommaException.
• If a general PunctuationException is caught, the program should print "The sentence does not end correctly."
• If a CommaException is caught, the program should print "You can't end a sentence in a comma."
• If there are no exceptions, the program should print "The sentence ends correctly." and terminate.

Use a catch block to catch all EndOfSentenceExceptions, causing the program to print a message and terminate.

public class EndOfSentenceException extends Exception
{
    public EndOfSentenceException(String str) 
    {
        super("The sentence ends correctly.");
    }
}
public class PunctuationException extends EndOfSentenceException
{
    public PunctuationException(String str) 
    {
        super("The sentence does not end correctly.");
    }
}
public class CommaException extends PunctuationException
{
    public CommaException(String str) 
    {
        super("You can't end a sentence in a comma.");
    }
}
public class Driver
{
    public static void checkSentence(String str)
            throws EndOfSentenceException
            {
                if(!(str.endsWith(".") || str.endsWith("!") || str.endsWith("?")))
                    {
                        throw new PunctuationException(str);
                    }
                if(str.endsWith(","))
                    {
                        throw new CommaException(str);
                    }
            }
    public static void main(String[] args) 
            throws EndOfSentenceException
    {
        //Initialize a scanner to take user input
        Scanner scan = new Scanner(System.in);
        String input = "";

        //Ask the user to input their sentence and assign it to input
        System.out.println("\nEnter a sentence:");
        input = scan.nextLine();

        try 
        {
            checkSentence(input);
            System.out.println("The Sentence ends correctly.");
        }
        catch(PunctuationException error)
        {
            System.out.println(error.getMessage());
        }
        catch(CommaException error)
        {
            System.out.println(error.getMessage());
        }
        scan.close();
    }
}

Answer 1

Exceptions in java should extend Throwable (usually this is Exception or RuntimeException ). Hence your custom exceptions could look like this:

public class PunctuationException extends Exception {
    public PunctuationException() {
         super("The sentence does not end correctly");
    }

    public PunctuationException(String message) {
        super(message);
    }
}

public class CommaException extends PunctuationException {
    public CommaException() {
        super("You can't end a sentence in a comma.");
    }
}

Second , the exception itself should not be responsible for check condition. This check should not be in exception.

class Driver {
    public static void main(String... args) {
        try {
            checkSentence("....");
            System.out.println("The sentence ends correctly.");
        } catch(PunctuationException e) {
            System.out.println(e.getMessage());
        }
    }

    public static void checkSentence(String str) throws PunctuationException {
        str = str != null ? str.trim() : null;

        if (str == null)
            return;
        if (!str.endsWith(".") && !str.endsWith("!") && !str.endsWith("?"))
            throw new PunctuationException();
        if (str.endsWith(","))
            throw new CommaException();
    }
}

Answer 2

I agree with oleg.cherednik.

And maybe, after you have made your custom exception classes like he mentioned, you can make the tester class like follow:

public class TesterClass{
    public void checkSentenceForException() {
     try {
         checkInputForEnding(input); //this function will throw the particular user-defined exception 
         System.out.println("The sentence ends correctly.");
     }
     catch(PunctuationException e) {
         //Desired exception output
     }
     catch(CommaException e) {
         //Desired exception output
     }
     finally {
         //if any cleanup is required
     }
    }
}

Do share if something better could be done.