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Question about the task

Factory method pattern

Java Core, Level 6, Lesson 13

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Hey guys, confused because as far as I can tell, if null is passed it will revert to default in switch? Thanks!

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; public class Solution { public static void main(String[] args) { ImageReader reader = ImageReaderFactory.getImageReader(ImageTypes.JPG); } }

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Justin Smith

Level 41 , Greenfield, USA, United States

17 September 2021, 15:10

You can get around this by remembering that a return statement stops further execution within the method. So you only need to test if the ImageTypes enum is equal to the 3 possibilities, return their matching classes, and then after the if block you can just throw the exception. As long as the method returns a matching class, it will never reach the throw statement.

Rich

Level 23 , San Diego, United States

29 January 2021, 15:25

little hint, you need to create an instance of the exception too

Thomas

Level 41 , Bayreuth, Germany

9 June 2020, 04:42

check what happens, if you give the getImageReader() method a null reference