Question

I am extending the BufferedImage class, to add some method like getRed, getBlue, getGreen for getting pixel color. The problem is that my original image is BufferedImage object not my extended object. When I try to cast to extended datatype, it isnt working.
Sorry for my English

I get this error

Exception in thread "main" java.lang.ClassCastException: java.awt.image.BufferedImage cannot be cast to asciiart.EBufferedImage

Code where I am trying to cast from parent class

EBufferedImage character = (EBufferedImage)ImageClass.charToImage(letter, this.matrix_x, this.matrix_y);

My extended class

public class EBufferedImage extends BufferedImage 
{
public EBufferedImage(int width, int height, int imageType)
{
    super(width,height,imageType); 
}

/**
* Returns the red component in the range 0-255 in the default sRGB
* space.
* @return the red component.
*/
public int getRed(int x, int y) {
    return (getRGB(x, y) >> 16) & 0xFF;
}

/**
* Returns the green component in the range 0-255 in the default sRGB
* space.
* @return the green component.
*/
public int getGreen(int x, int y) {
    return (getRGB(x, y) >> 8) & 0xFF;
}

/**
* Returns the blue component in the range 0-255 in the default sRGB
* space.
* @return the blue component.
*/
public int getBlue(int x, int y) {
    return (getRGB(x, y) >> 0) & 0xFF;
}
}

Answer 1

You have a couple options:

1. Add a constructor to the extended class that accepts a BufferedImage and sets everything appropriately.

   public class ExtendedBufferedImage extends BufferedImage{
   
     public ExtendedBufferedImage(BufferedImage image){
         //set all the values here
     }
   
     //add your methods below
   }
   

   This one seems like a lot of work and potential for issues. If you forget to set some variable you could introduce some weird bugs, or lose information you need.

2. Create a wrapper class that has an instance of a BufferedImage, and then add your methods in.

   public class ExtendedBufferedImage{
     private BufferedImage image;  
   
     public ExtendedBufferedImage(BufferedImage image){
        this.image = image;
     }
   
     //add your methods below
   }
   

   This is pretty reasonable, and is not to diffcult. Make the BufferedImage public or add a getter method and you can get the actual BufferedImage out of it if you need that.

3. Create a Utility class that has your methods as being static and pass in the BufferedImage as a parameter.

   public class BufferedImageUtil{
   
     public static int getRed(BufferedImage image, int x, int y) {
       return (image.getRGB(x, y) >> 16) & 0xFF;
     }
   
     //add your other methods
   }
   

   Some people don’t like utility Classes, but I kind of like them for things like this. If you are going to use these methods all over the place, I think this is a good option.

Personally I would go the utility class route, but if you don’t like those then wrapping it as done in option 2 is just as functional.