CodeGym/Help with Java Tasks/Can someone help me in this task

Level 22

Nagpur

13.12.2018
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14comments

Can someone help me in this task

Question about the task

Factory method pattern

Java Core, Level 6, Lesson 13

Resolved

Last condition is not satisfying

1. Take a careful look at the classes you have.
2. In separate files in the common package, create JpgReader, PngReader, and BmpReader classes that implement the ImageReader interface.
3. In a separate file in the main package, create the ImageReaderFactory class with one method.
3.1. Think about what it should be called.
3.2. Think about which modifiers this method should have.
4. This method should:
4.1. For each value in ImageTypes, return the appropriate Reader. For example, for
ImageTypes.JPG, return a JpgReader;
4.2. If an invalid argument is passed, then throw an exception:
IllegalArgumentException("Unknown image type").

Requirements:

Create a JpgReader class in the common package. It must implement the ImageReader interface.
Create a PngReader class in the common package. It must implement the ImageReader interface.
Create a BmpReader class in the common package. It must implement the ImageReader interface.
Create a public class named ImageReaderFactory.
Add a public static method getImageReader with an ImageTypes parameter to the ImageReaderFactory class.
The getImageReader method must create and return a suitable Reader.
The getImageReader method must throw an IllegalArgumentException if an invalid argument is passed.

package com.codegym.task.task16.task1631; import com.codegym.task.task16.task1631.common.ImageReader; import com.codegym.task.task16.task1631.common.ImageTypes; import com.codegym.task.task16.task1631.common.*; /* Requirements: 1. Create a JpgReader class in the common package. It must implement the ImageReader interface. 2. Create a PngReader class in the common package. It must implement the ImageReader interface. 3. Create a BmpReader class in the common package. It must implement the ImageReader interface. 4. Create a public class named ImageReaderFactory. 5. Add a public static method getImageReader with an ImageTypes parameter to the ImageReaderFactory class. 6. The getImageReader method must create and return a suitable Reader. 7. The getImageReader method must throw an IllegalArgumentException if an invalid argument is passed. */ public class Solution { public static void main(String[] args) { try{ ImageReader reader = ImageReaderFactory.getImageReader(null); }catch(Exception ex){ ex.printStackTrace(); } } }

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Shamil

Level 19 , Kyiv, Ukraine

1 August 2022, 16:11

My mistake: throw wrong exception with similar name. 13 attempts😁

Guadalupe Gagnon

Level 37 , Tampa, United States

10 September 2020, 13:42

My first response to this task i made when I was still learning how to code back in 2018. I had originally passed this task using if else statements to check that the type was equal to one of the accepted types:

if(type == ImageTypes.JPG)
   //...
else if (type == BMP)
else if(type == PNG)

And if none of them were true then it would throw the exception. This code worked for me. Now, with the code from above, the problem is that switch statements will throw a NullPointerException if the variable passed to the switch statement is null. What I didn't realize back then was that my solution to the problem worked because the equality check (==) can check for null values where switch statements can not. If a switch statement is used, as pointed out in many of the prior posts, then the code MUST include a check for null before the execution of the switch statement. Not doing can expose your code to the NullPointerException possibility, and will fail verification.

Sela

Level 20 , Poland

5 August 2020, 13:26

to assume that

ImageTypes x = null;

then

String.valueOf(x)

evaluates to

"null"

which is a String object, note - not an Exception. but

x.equals(x)

throws the NullPointerException. other words you can use

"null".equals("null")

but

x.equals("null")

throws an Exception

Paweł Ż

Level 18 , Warsaw, Poland

24 September 2019, 15:10

Hi there is one thing missing. In method declaration you must declare what exception method can throw (we talked about exception w/o catch)

public static ImageReader getImageReader(ImageTypes type) throws IllegalArgumentException {
....
}

thats all in my opinion :)

Ewerton Backend Developer

2 July 2019, 19:14

public class ImageReaderFactory {
    public static ImageReader getImageReader(ImageTypes format){
        if (String.valueOf(format).equals("JPG")) return new JpgReader();
        if (String.valueOf(format).equals("PNG")) return new PngReader();
        if (String.valueOf(format).equals("BMP")) return new BmpReader();
        throw new IllegalArgumentException("Unknown image type");
    }
}

Maybe it's your comparison method? This code here works fine.

Rafał Kudzia

Level 18 , Katowice, Poland

12 February 2020, 16:56

public class ImageReaderFactory { public static ImageReader getImageReader(ImageTypes x) { if (x.equals(ImageTypes.JPG)) return new JpgReader(); if (x.equals(ImageTypes.PNG)) return new PngReader(); if (x.equals(ImageTypes.BMP)) return new BmpReader(); throw new IllegalArgumentException("Unknown image type"); } Whyyyy Ererton's code works fine and mine don't pass last condition??? It doesn't make sense for me. Can somebody explain it??

Guadalupe Gagnon

Level 37 , Tampa, United States

13 December 2018, 16:32

Your code seems to work according to the conditions. That means that either 1) it is a bugged problem and won't verify; 2) there is a small spelling error somewhere; or 3) some superfluous code is causing you to fail. Double check your code carefully in case there is a small spelling error, then if none are found try to remove unnecessary code and resubmit. I suggest rewriting your method such as this:

public static ImageReader getImageReader(ImageTypes type){

        switch(type) {
            case JPG :
                return new JpgReader();
            case PNG :
                return new PngReader();
            case BMP :
                return new BmpReader();
            default :
                throw new IllegalArgumentException("Unknown image type");
        }
    }

Abhishek Rangari

Level 22 , Nagpur, India

17 December 2018, 18:55

this little piece of code works fine

static ImageTypes it;

        public static ImageReader getImageReader(ImageTypes type){

         if(it == null){
                //throw new IllegalArgumentException("Unknown image type");
         }

        if(type == ImageTypes.BMP){
            return new BmpReader();
        }else if(type == ImageTypes.PNG){
            return new PngReader();
        }else if(type == ImageTypes.JPG){
            return new JpgReader();
        }else{
            throw new IllegalArgumentException("Unknown image type");
        }
    }

though thanks for your help..

Bill Wu

Level 29 , Wellington, New Zealand

23 February 2019, 18:54

I wrote the same code as this, but it won't pass because it throws NullPointerException. I have to clearly indicate the case of null in the method to throw the IllegalArgumentException("Unknown image type").

if (type==null) throw new IllegalArgumentException("Unknown image type");
       switch(type) {
           case JPG :
               return new JpgReader();
           case PNG :
               return new PngReader();
           case BMP :
               return new BmpReader();
           default :
               throw new IllegalArgumentException("Unknown image type");
       }

Abhishek Rangari

Level 22 , Nagpur, India

2 March 2019, 15:14

Can you please closely look on the code snippet which I provided, as when you say you used the same code it does not look same.

Bill Wu

Level 29 , Wellington, New Zealand

2 March 2019, 18:47

Sorry I mean same with the code of Guadalupe...

Jesús de Llera

Level 23 , Badajoz, Spain

18 May 2019, 16:21

I had the exact same code as Guadalupe, but for some strange reason the code was not verifying if I placed the "throw" inside a default clause. I had to add an if outside the switch to pass.

public static ImageReader getImageReader(ImageTypes imageTypes) {

        if (imageTypes == null) throw new IllegalArgumentException("Unknown image type");

        switch (imageTypes) {
            case JPG:
                return new JpgReader();
            case PNG:
                return new PngReader();
            case BMP:
                return new BmpReader();
        }

        return null;

    }

+10

AlfredW

Level 23 , Denver, United States

9 September 2020, 21:44

I had to add to this. For some reason it would not validate with just the default case. So I threw in a line to catch it before hand.

public class ImageReaderFactory {
    public static ImageReader getImageReader(ImageTypes type){
        if (type == null){throw new IllegalArgumentException("Unknown image type");}

        switch(type) {
            case JPG :
                return new JpgReader();
            case PNG :
                return new PngReader();
            case BMP :
                return new BmpReader();
            default :
                throw new IllegalArgumentException("Unknown image type");
        }
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

10 September 2020, 13:44

To posters interested in why: see my post above dated 9 September 2020