CodeGym/Help with Java Tasks/last condition

Level 33

Mumbai

05.12.2019
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last condition

Question about the task

Resolved

The error shows "If any exception other than a NoSuchZipFileException occurs, then display "An error occurred. Please check the entered data." .please help

To find out which command the user currently wants to execute, let's add an Operation
askOperation() method to the Archiver class. This method should display a list of available commands and
ask the user to choose one of them. For convenience, we will ask the user to enter the command's number, which is its
ordinal number in the Operation enum. You can get an enum field's ordinal number using the ordinal() method.
Now everything is ready to rewrite the main method using our latest scientific advancements, specifically
the CommandExecutor class and the askOperation() method.
1. Add a public static Operation askOperation() throws IOException method to the Archiver class.
It must: 1.1. Use the ConsoleHelper class's methods
1.2. Ask the user for the number of the desired operation.

Hint:
To display the number of the "Create archive" operation, use: Operation.CREATE.ordinal()

1.3. Return the selected operation.
Example output of the askOperation() method:


Select an operation:0 - Zip files into an archive
1 - Add a file to an archive
2 - Remove a file from an archive
3 - Extract an archive
4 - View the contents of an archive
5 - Exit

2. Rewrite the main() method:
2.1. Declare a local Operation variable
2.2. In a loop, use the askOperation() method to ask for a new value for the variable in step 2.1, and use CommandExecutor.execute() to perform the operation.
2.3. Allow the user to exit the loop by selecting the Operation.EXIT operation
2.4. Wrap the askOperation() and execute(operation) calls in a try-catch block. If a NoSuchZipFileException occurs, use ConsoleHelper to display "You didn't select an archive or you selected an invalid file." If any other exceptions occur, display "An error occurred. Please check the entered data."
2.5. Be sure that the program continues running (continues to a new iteration of the loop) after handling exceptions.
3. Run the program and verify that the "exit" command works.

Requirements:

You need to create a public static Operation askOperation() method in the Archiver class.
The askOperation method should display all of the possible operations and their numbers.
The askOperation method should read the selected operation's number from the keyboard and return it.
Rewrite the main method according to the task conditions.

package com.codegym.task.task31.task3110; import com.codegym.task.task31.task3110.command.ExitCommand; import com.codegym.task.task31.task3110.exception.PathNotFoundException; import com.codegym.task.task31.task3110.exception.NoSuchZipFileException; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.nio.file.Path; import java.nio.file.Paths; public class Archiver { public static void main(String[] args) throws IOException{ Operation operation = null; try{ operation = askOperation(); CommandExecutor.execute(operation); }catch (Exception e){} while(operation != Operation.EXIT){ try{ operation = askOperation(); CommandExecutor.execute(operation); }catch (NoSuchZipFileException e){ ConsoleHelper.writeMessage("You didn't select an archive or you selected an invalid file."); }catch (Exception e){ ConsoleHelper.writeMessage("An error occurred.Please check the entered data."); } } } public static Operation askOperation() throws IOException{ Operation op = null; ConsoleHelper.writeMessage("Select an operation: "+Operation.CREATE.ordinal()+" - Create an archive"); ConsoleHelper.writeMessage(Operation.ADD.ordinal()+" - Add a file to an archive"); ConsoleHelper.writeMessage(Operation.REMOVE.ordinal()+" - Remove a file from an archive"); ConsoleHelper.writeMessage(Operation.EXTRACT.ordinal()+" - Extract an archive"); ConsoleHelper.writeMessage(Operation.CONTENT.ordinal()+" - View the content of an archive"); ConsoleHelper.writeMessage(Operation.EXIT.ordinal()+" - Exit"); int c = ConsoleHelper.readInt(); for(Operation opp : Operation.values()){ if(opp.ordinal() == c) op = opp; } return op; } }

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Abe

Level 41 , Salt Lake City, United States

5 December 2019, 15:31

solution

I think the issue is with the first choice in the main method. The way the method is currently written, it is possible to get a NoSuchZipFileException on the first choice, but it is not handled as the task dictates (lines 17-20) The change I would suggest is to switch your while loop in lines 22-32 of the main method into a do-while loop and take out lines 17-20. This way, any exceptions are caught and handled per the task requirements from the very first selection on.

Niladri pradhan

Level 33 , Mumbai, India

6 December 2019, 06:24

Thank You

Henrique

Level 41 , São Paulo, Brazil

12 August 2020, 17:29

Can you help me? How to do that what was suggested???

jpcouturier

Level 29 , France, France

26 February, 15:05

well... I think this task needs a do {} while(); but I don't know why ? when you have this, it passed :

public static void main(String[] args) {
        Operation operation = null;

        do
        {
            try
            {
                operation = askOperation();
                CommandExecutor.execute(operation);
            }
            catch (Exception e)
            {
                if(e instanceof NoSuchZipFileException)
                    ConsoleHelper.writeMessage("You didn't select an archive or you selected an invalid file.");
                else
                    ConsoleHelper.writeMessage("An error occurred. Please check the entered data.");
            }
        }
        while(operation != Operation.EXIT);
    }

But when you have this, the test doesn't pass... If an expert can tell me why ? :

public static void main(String[] args) {
        Operation operation;

        while(true)
        {
            try
            {
                operation = askOperation();
                CommandExecutor.execute(operation);

                if(operation.equals(Operation.EXIT))
                    break;
            }
            catch (Exception e)
            {
                if(e instanceof NoSuchZipFileException)
                    ConsoleHelper.writeMessage("You didn't select an archive or you selected an invalid file.");
                else
                    ConsoleHelper.writeMessage("An error occurred. Please check the entered data.");
            }
        }
    }

Guadalupe Gagnon

Level 37 , Tampa, United States

26 February, 17:04

In regard to enums and .equals() versus ==/!=: https://stackoverflow.com/questions/1750435/comparing-java-enum-members-or-equals Basically using equals() can result in a null pointer exception while ==/!= are null safe

Operation test = null;
Operation test2 = *any valid Operation or null*

System.out.println(test == test2); // OK
System.out.println(test.equals(test2)); // null pointer exception

In jpcouturier's two examples the only thing that I see that could be causing an issue is that if askOperation() returns Operation.Exit and then an exception occurs at line 9 (in both examples); In the first example while(operation != Operation.EXIT); would be checked after the Exception was caught while in the second example lines 11 and 12 would effectively be skipped and the loop would continue.

jpcouturier

Level 29 , France, France

27 February, 10:48

Thanks for your answer. The difference is subtile and wasn't asked in the requirements. The validator seems ask to manage to never be blocked with the Operation.EXIT command If that's it, I think the following code must be work (I can't try it because code is already validated) :

public static void main(String[] args) {
        Operation operation;

        while(true)
        {
            try
            {
                operation = askOperation();
                CommandExecutor.execute(operation);

                if(operation.equals(Operation.EXIT))
                    break;
            }
            catch (Exception e)
            {
                if(e instanceof NoSuchZipFileException)
                    ConsoleHelper.writeMessage("You didn't select an archive or you selected an invalid file.");
                else
                {
                    ConsoleHelper.writeMessage("An error occurred. Please check the entered data.");
                    if(operation.equals(Operation.EXIT))
                         break;
                }
            }
        }
    }

Guadalupe Gagnon

Level 37 , Tampa, United States

27 February, 14:27

You should pretty much always use == or != with enumerations and it would also be better to do the loop break check in a finally block:

Operation operation = null;

while(true) {
   try {
      operation = askOperation();
      CommandExecutor.execute(operation);
   } catch (Exception e) {
      if(e instanceof NoSuchZipFileException)
         ConsoleHelper.writeMessage("You didn't select an archive or you selected an invalid file.");
      else
         ConsoleHelper.writeMessage("An error occurred. Please check the entered data.");
   } finally {
      if(operation == Operation.EXIT) break;
   }
}

jpcouturier

Level 29 , France, France

28 February, 14:32

Ok, thanks for advices ;)