Maxi Contieri

Posted on Nov 16, 2020 • Edited on Jul 13, 2021 • Originally published at maximilianocontieri.com

Code Smell 26 - Exceptions Polluting

#oop #exceptions #tutorial #programming

It is very nice to have lots of different exceptions. Your code is declarative and robust. Or not?

TL;DR; Don't create anemic and empty objects. Even if they are Exceptions.

Problems

Over Design
Namespace Pollution

Solutions

Avoid creating anemic exceptions as globals.
Create exceptions only if they behave differently.
Model exceptions with objects. Classes are handy for lazy programmers.

Sample Code

Wrong

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class FileReader {

    public static void main(String[] args) {
        FileReader file = null;

        try {
            file = new FileReader("source.txt");
            file.read();
        }
        catch(FileNotFoundException e) {
            e.printStackTrace();
        }
        catch(FileLockedException e) {
            e.printStackTrace();
        }
        catch(FilePermissionsException e) {
            e.printStackTrace();
        }
        catch(IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                file.close();
            }
            catch(IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Right

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class FileReader {

    public static void main(String[] args) {
        FileReader file = null;

        try {
            file = new FileReader("source.txt");
            file.read();
        }
        catch(FileException exception) {
            if (exception.description == (this.expectionMessages().errorDescriptionFileTemporaryLocked() {
                //sleep and retry    
                //IF behaviour is the same with all the exceptions just change the text on object creation and raise the icorrect instance
            }            
            this.showErrorToUser(exception.messageToUser();
             //This example is simplified. Text should be translated
        }                
        finally {
            try {
                file.close();
            } 
        }
    }
}

Detection

New exceptions should override behavior methods.

No. code, description, resumable, etc. are not behavioral.

Conclusion

You would not create different classes for every Person instance, so they return different names. Why would you do it with exceptions.

How often do you catch a specific exception?.

Go out and check your code.

Is it necessary to be a class?

You are already coupled to the class. Couple to the description instead.

Exception instances should NOT be Singletons.

Relations

Code Smell 01 - Anemic Models

Maxi Contieri ・ Oct 20 '20

#codenewbie #oop #beginners #computerscience

Credits

Photo by Nick van den Berg on Unsplash

You will fall to ruin because you believe that exceptions to the rule make new rules.

Pierce Brown

Software Engineering Great Quotes

Maxi Contieri ・ Dec 28 '20

#codenewbie #programming #quotes #software

This article is part of the CodeSmell Series.

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