Please gelp me! Last condition..

Question about the task

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What's wrong? I don't understand

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

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Guadalupe Gagnon

Level 37 , Tampa, United States

29 December 2020, 20:43

solution

#1 You should not use static variables unless there is a reason to do so. There is no reason in this task. Get rid of the class field (line 6 of the ImageReaderFactory class) and make that a local variable within the method it is used. #2 calling any methods on a null object will end up with a NullPointerException being thrown. The correct way to test for null is to use the double equals sign:

String object = null
System.out.println(object == null); // this will print true

// ↓ this results in a NullPointerException and program crash
System.out.println(object.equals(null));

#3 Checking for null should ALWAYS be the first check as any methods called on a null object will cause the exception, and if uncaught, will crash the program.

// incorrect
if(object.equals(anotherObject) { } // this will crash program if object is null
else if(object == null) { } // this code wont be reached

// correct
if(object == null) { /*code to handle null*/ }
else if(object.equals(anotherObject) { } // this won't crash now because
// first 'if' statement 'catches' all null objects

Vitalina

Level 20 , Poland

29 December 2020, 21:14

Thank you. I understood everything!