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();
            } 
        }
    }
}