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Comp301 Assignment 6-image Solution
Introduction
This assignment gives practice with the decorator design pattern. To complete the assignment, you will create a series of base classes and decorator classes to collectively represent a digital image, like what you would see on Snapchat or Instagram.
In this context, the decorator pattern will be used to add visual modifications to a starting image. For example, one decorator class you will make adds a border around an existing image; another decorator superimposes a configurable circle somewhere on the image. The order in which you add the decorators to the base image will determine the order in which the modifications will appear on the final result.
Colors
Painters like Bob Ross can create new colors of paint by combining three primary colors of paint in different proportions. Computers use the same approach to represent and display all the different colors you see on your screen. For a computer, the three primary colors are red, green, and blue. Every color on your screen is a combination of different proportions of red, green, and blue.
Most computer systems represent a color using three numbers in the range 0-255. For example, (0, 255, 52) represents a greenish color. The first number corresponds to the amount of red present in the color, the second number corresponds to the amount of green, and the third corresponds to the amount of blue. This color therefore has no red, 255 green, and 52 blue. Since the color has the maximum amount of green, we could expect the color to be mostly green, mixed with a little blue.
Java provides a built-in Color class for representing colors. The color class encapsulates a red, blue, and green value in the range 0-255. Here's how to create a new Color instance: java Color greenish = new Color(0, 255, 52);
Now greenish is an object representing the greenish color described above.
Image interface
Every class you will create for this assignment should implement the Image interface, which is already provided in the starter code. An Image object represents a digital image. Digital images are made up of a two-dimensional grid of "pixels", which are essentially minuscule rectangles of color.
Every Image has a width and a height, referring to the number of horizontal and vertical pixels in the image. The Image interface therefore has getWidth() and getHeight() getter methods for getting these values.
To get the color of a pixel, use the getPixelColor() method. getPixelColor() takes an x and a y value as parameters, representing the location of the pixel to get. And getPixelColor() returns a Color object, representing the color of the requested pixel.
The Image interface also has a numLayers() getter method for getting the number of "layers" in the image. Base images, which do not have any decorators, have only one layer. Each decorator added to an image (like a shape or a border) is another "layer" added to the image. So, for instance, if a base image has one border decorator and one square decorator, then the image has a total of 3 layers.
Novice
For the novice portion of the assignment, create two new classes implementing the Image interface: SolidColorImage, and PictureImage. These classes represent base images themselves---they do not decorate another image.
SolidColorImage
The SolidColorImage class represents a blank image that is a solid color, kind of like a background. This class is a good starting point for making images that consist mostly of decorators stacked on top of each other.
Add a new class to your project called SolidColorImage which implements the Image interface. You'll have to add getPixelColor(), getWidth(), getHeight(), and numLayers() methods in order to implement the interface. SolidColorImage should have only one constructor with the following signature:
java public SolidColorImage(int width, int height, Color color) { // Constructor code goes here }
Encapsulate width, height, and color as private fields in the class. They represent the width, height, and color of the image. Make sure to check for illegal values of height and width (negative values are illegal), and throw an IllegalArgumentException if an illegal value is detected.
getWidth() and getHeight() should act as basic getter methods for their corresponding fields. getPixelColor() should retrieve and return the color of the pixel at the specified (x, y) location in the image. Since this class represents a solid color image, all pixel values have the same color. Therefore, getPixelColor() should return the same color for all pixel locations---that is, the color encapsulated as a private field. However, getPixelColor() should also check to make sure the specified coordinates are actually within the boundaries of the image. For example, if the provided x value is negative or if it is greater or equal to the width of the image, then the coordinate is invalid. If an invalid coordinate is detected, throw an IllegalArgumentException. Finally, the getNumLayers() method should always return 1, since base images only have one layer.
You should now be able to create and use new instances of SolidColorImage. Test out your new class in the Main file by making and returning a new instance inside the static makeImage() method. Make an image that is 200 by 200 images large, and is the greenish color described above. Run the main method to see your image on the screen.
PictureImage
The other base image class to create for this assignment is PictureImage, which represents an existing image from your computer. This class is a good starting point for adding decorators on top of an existing image.
PictureImage should implement the Image interface, and should have a single constructor with the following signature:
java public PictureImage(String pathname) throws IOException { // Constructor code goes here }
The pathname parameter represents the path of an image stored on your computer. You should be able to complete the implementation for the entire PictureImage class by encapsulating only one field, which stores a BufferedImage object. In the constructor, use the pathname parameter to create a BufferedImage object, and store it in a private field. A BufferedImage represents an image from your computer which has been read into memory. You can read more about it here. In particular, you'll have to use BufferedImage's getWidth(), getHeight(), and getRGB() methods to complete the PictureImage class.
When you're done, test out your PictureImage class by making and returning an instance of PictureImage from the makeImage() static method located in the Main.java file. If you use "img/kmp.jpg" as the pathname argument, you should see a picture of kmp when running the main() method.
Adept
Now it's time to start making decorator classes for the Image interface. Remember, decorator objects need to encapsulate an instance of the same interface that they implement. That means all the decorator classes created for this assignment should both implement Image, and they should encapsulate an instance of an Image object as a private field.
SquareDecorator
This decorator class should superimpose a configurable square on top of an existing image. The constructor should have the following signature:
java public SquareDecorator(Image image, int squareX, int squareY, int squareSize, Color color) { // Constructor code goes here }
Parameters squareX and squareY represent the coordinates of the top left of the square. Parameter squareSize represents the side length of the square. The color parameter represents the color of the square. Finally, the image parameter represents the underlying image that is being painted over. Make sure to check for illegal argument values in the constructor, and throw an IllegalArgumentException if one occurs. In particular, if image is null or if the square size is negative, these are considered illegal arguments.
When getPixelColor() is called, the specified (x, y) coordinates should be checked to see if they are within the bounds of the square. If they
are inside the square, then the returned color should be the designated square color (regardless of the underlying image's pixel value at that location). If the coordinates are outside the square, then the pixel's color should be unaffected by the decorator. In this case, simply return the underlying image's pixel value at that location.
Note: Digital images, including the ones in this assignment, traditionally use a coordinate system with an inverted y-axis. In other words, pixel (0, 0) is the top-left-most pixel in the picture; pixels to the right of that pixel have positive x-coordinate values, and pixels below the pixel have positive y-coordinate values. Here is an article with more information about the coordinate system for digital images.
CircleDecorator
This decorator is very similar to SquareDecorator, except it decorates the underlying image with a circle instead of with a square. The constructor should have the following signature:
java public CircleDecorator(Image image, int cx, int cy, int radius, Color color) { // Constructor code goes here }
The center of the circle should be located at position (cx, cy) in the image, should have radius radius, and should have color color. A pixel should be considered "in the circle" (and should therefore be painted with the color stored in color) if its (x, y) location is strictly less than radius units away from the center, (cx, cy). You can use the distance formula to calculate how close a pixel is from the center of the circle. Negative radius values should not be allowed (i.e., a IllegalArgumentException should be thrown if one is detected).
Jedi
This section involves creating two more Image decorator classes: BorderDecorator, and ZoomDecorator.
BorderDecorator
The BorderDecorator class decorates an image by surrounding it with a solid-color border. The class should implement Image and should have the following constructor signature:
java public BorderDecorator(Image image, int thiccness, Color borderColor) { // Constructor code goes here }
thiccness represents the thickness of the border, and borderColor represents the color of the border. Negative values of thiccness should not be allowed, and if one is detected, an IllegalArgumentException should be thrown.
BorderDecorator should expand the height and width of the underlying image to account for the border being added. For example, if thiccness is 10, that means 20 pixels should be added to the width of the image---10 pixels for the left border, and 10 pixels for the right border. A similar computation should take place for the top and bottom borders.
ZoomDecorator
The ZoomDecorator class decorates an existing image by scaling the image so that it appears larger. ZoomDecorator should provide two constructors. The first constructor has the following signature:
java public ZoomDecorator(Image image, int multiplier) { // Constructor code goes here }
Here, multiplier is a positive integer referring to the factor by which the image should be scaled. A multiplier of 1 indicates that the image should not be scaled at all. A multiplier of 2 means the width and height should be doubled; a multiplier of 3 means the width and height should be tripled, and so on. Invalid values of multiplier should throw an IllegalArgumentException.
The other constructor should omit the multiplier parameter, and instead should use a default multiplier value of 2. Use constructor chaining to accomplish this.
In addition to simply increasing the width and height of the image, this class should also stretch the original image to fit the new size. This modification should take place in the getPixelColor() method. For example, if the original image has a height and width of 2, and the zoom multiplier is 2, then the decorated image should have a height of 4 and a width of 4, but the underlying pixels should be scaled so that
getPixelColor(0, 0), getPixelColor(0, 1), getPixelColor(1, 0), and getPixelColor(1, 1) all return the same pixel color---that
is, they return the same color as the pixel located at position (0, 0) in the original picture. In other words, each pixel value in the original pixel should be mapped to four pixels in the scaled image.
Putting it all together
Finally, in Main.java, adjust the makeImage() method so that it creates and returns an Image object using the decorator pattern with the following properties:
The base image should be img/kmp.jpg
The red border is color (255, 0, 0) and has a thickness of 5 (before scaling)
The blue border is color (0, 0, 255) and has a thickness of 50 (before scaling)
The yellow circle is color (255, 255, 0), has radius 40 (before scaling), and is at position (50, 50) in the final, unscaled image
The orange square is color (200, 80, 10), has size 40 (before scaling), and is at position (100, 100) in the final, unscaled image After applying these decorators, add one last ZoomDecorator with a multiplier of 2, to make the image bigger
You can see an example of the final image in img/jedi.png.
This assignment gives practice with the decorator design pattern. To complete the assignment, you will create a series of base classes and decorator classes to collectively represent a digital image, like what you would see on Snapchat or Instagram.
In this context, the decorator pattern will be used to add visual modifications to a starting image. For example, one decorator class you will make adds a border around an existing image; another decorator superimposes a configurable circle somewhere on the image. The order in which you add the decorators to the base image will determine the order in which the modifications will appear on the final result.
Colors
Painters like Bob Ross can create new colors of paint by combining three primary colors of paint in different proportions. Computers use the same approach to represent and display all the different colors you see on your screen. For a computer, the three primary colors are red, green, and blue. Every color on your screen is a combination of different proportions of red, green, and blue.
Most computer systems represent a color using three numbers in the range 0-255. For example, (0, 255, 52) represents a greenish color. The first number corresponds to the amount of red present in the color, the second number corresponds to the amount of green, and the third corresponds to the amount of blue. This color therefore has no red, 255 green, and 52 blue. Since the color has the maximum amount of green, we could expect the color to be mostly green, mixed with a little blue.
Java provides a built-in Color class for representing colors. The color class encapsulates a red, blue, and green value in the range 0-255. Here's how to create a new Color instance: java Color greenish = new Color(0, 255, 52);
Now greenish is an object representing the greenish color described above.
Image interface
Every class you will create for this assignment should implement the Image interface, which is already provided in the starter code. An Image object represents a digital image. Digital images are made up of a two-dimensional grid of "pixels", which are essentially minuscule rectangles of color.
Every Image has a width and a height, referring to the number of horizontal and vertical pixels in the image. The Image interface therefore has getWidth() and getHeight() getter methods for getting these values.
To get the color of a pixel, use the getPixelColor() method. getPixelColor() takes an x and a y value as parameters, representing the location of the pixel to get. And getPixelColor() returns a Color object, representing the color of the requested pixel.
The Image interface also has a numLayers() getter method for getting the number of "layers" in the image. Base images, which do not have any decorators, have only one layer. Each decorator added to an image (like a shape or a border) is another "layer" added to the image. So, for instance, if a base image has one border decorator and one square decorator, then the image has a total of 3 layers.
Novice
For the novice portion of the assignment, create two new classes implementing the Image interface: SolidColorImage, and PictureImage. These classes represent base images themselves---they do not decorate another image.
SolidColorImage
The SolidColorImage class represents a blank image that is a solid color, kind of like a background. This class is a good starting point for making images that consist mostly of decorators stacked on top of each other.
Add a new class to your project called SolidColorImage which implements the Image interface. You'll have to add getPixelColor(), getWidth(), getHeight(), and numLayers() methods in order to implement the interface. SolidColorImage should have only one constructor with the following signature:
java public SolidColorImage(int width, int height, Color color) { // Constructor code goes here }
Encapsulate width, height, and color as private fields in the class. They represent the width, height, and color of the image. Make sure to check for illegal values of height and width (negative values are illegal), and throw an IllegalArgumentException if an illegal value is detected.
getWidth() and getHeight() should act as basic getter methods for their corresponding fields. getPixelColor() should retrieve and return the color of the pixel at the specified (x, y) location in the image. Since this class represents a solid color image, all pixel values have the same color. Therefore, getPixelColor() should return the same color for all pixel locations---that is, the color encapsulated as a private field. However, getPixelColor() should also check to make sure the specified coordinates are actually within the boundaries of the image. For example, if the provided x value is negative or if it is greater or equal to the width of the image, then the coordinate is invalid. If an invalid coordinate is detected, throw an IllegalArgumentException. Finally, the getNumLayers() method should always return 1, since base images only have one layer.
You should now be able to create and use new instances of SolidColorImage. Test out your new class in the Main file by making and returning a new instance inside the static makeImage() method. Make an image that is 200 by 200 images large, and is the greenish color described above. Run the main method to see your image on the screen.
PictureImage
The other base image class to create for this assignment is PictureImage, which represents an existing image from your computer. This class is a good starting point for adding decorators on top of an existing image.
PictureImage should implement the Image interface, and should have a single constructor with the following signature:
java public PictureImage(String pathname) throws IOException { // Constructor code goes here }
The pathname parameter represents the path of an image stored on your computer. You should be able to complete the implementation for the entire PictureImage class by encapsulating only one field, which stores a BufferedImage object. In the constructor, use the pathname parameter to create a BufferedImage object, and store it in a private field. A BufferedImage represents an image from your computer which has been read into memory. You can read more about it here. In particular, you'll have to use BufferedImage's getWidth(), getHeight(), and getRGB() methods to complete the PictureImage class.
When you're done, test out your PictureImage class by making and returning an instance of PictureImage from the makeImage() static method located in the Main.java file. If you use "img/kmp.jpg" as the pathname argument, you should see a picture of kmp when running the main() method.
Adept
Now it's time to start making decorator classes for the Image interface. Remember, decorator objects need to encapsulate an instance of the same interface that they implement. That means all the decorator classes created for this assignment should both implement Image, and they should encapsulate an instance of an Image object as a private field.
SquareDecorator
This decorator class should superimpose a configurable square on top of an existing image. The constructor should have the following signature:
java public SquareDecorator(Image image, int squareX, int squareY, int squareSize, Color color) { // Constructor code goes here }
Parameters squareX and squareY represent the coordinates of the top left of the square. Parameter squareSize represents the side length of the square. The color parameter represents the color of the square. Finally, the image parameter represents the underlying image that is being painted over. Make sure to check for illegal argument values in the constructor, and throw an IllegalArgumentException if one occurs. In particular, if image is null or if the square size is negative, these are considered illegal arguments.
When getPixelColor() is called, the specified (x, y) coordinates should be checked to see if they are within the bounds of the square. If they
are inside the square, then the returned color should be the designated square color (regardless of the underlying image's pixel value at that location). If the coordinates are outside the square, then the pixel's color should be unaffected by the decorator. In this case, simply return the underlying image's pixel value at that location.
Note: Digital images, including the ones in this assignment, traditionally use a coordinate system with an inverted y-axis. In other words, pixel (0, 0) is the top-left-most pixel in the picture; pixels to the right of that pixel have positive x-coordinate values, and pixels below the pixel have positive y-coordinate values. Here is an article with more information about the coordinate system for digital images.
CircleDecorator
This decorator is very similar to SquareDecorator, except it decorates the underlying image with a circle instead of with a square. The constructor should have the following signature:
java public CircleDecorator(Image image, int cx, int cy, int radius, Color color) { // Constructor code goes here }
The center of the circle should be located at position (cx, cy) in the image, should have radius radius, and should have color color. A pixel should be considered "in the circle" (and should therefore be painted with the color stored in color) if its (x, y) location is strictly less than radius units away from the center, (cx, cy). You can use the distance formula to calculate how close a pixel is from the center of the circle. Negative radius values should not be allowed (i.e., a IllegalArgumentException should be thrown if one is detected).
Jedi
This section involves creating two more Image decorator classes: BorderDecorator, and ZoomDecorator.
BorderDecorator
The BorderDecorator class decorates an image by surrounding it with a solid-color border. The class should implement Image and should have the following constructor signature:
java public BorderDecorator(Image image, int thiccness, Color borderColor) { // Constructor code goes here }
thiccness represents the thickness of the border, and borderColor represents the color of the border. Negative values of thiccness should not be allowed, and if one is detected, an IllegalArgumentException should be thrown.
BorderDecorator should expand the height and width of the underlying image to account for the border being added. For example, if thiccness is 10, that means 20 pixels should be added to the width of the image---10 pixels for the left border, and 10 pixels for the right border. A similar computation should take place for the top and bottom borders.
ZoomDecorator
The ZoomDecorator class decorates an existing image by scaling the image so that it appears larger. ZoomDecorator should provide two constructors. The first constructor has the following signature:
java public ZoomDecorator(Image image, int multiplier) { // Constructor code goes here }
Here, multiplier is a positive integer referring to the factor by which the image should be scaled. A multiplier of 1 indicates that the image should not be scaled at all. A multiplier of 2 means the width and height should be doubled; a multiplier of 3 means the width and height should be tripled, and so on. Invalid values of multiplier should throw an IllegalArgumentException.
The other constructor should omit the multiplier parameter, and instead should use a default multiplier value of 2. Use constructor chaining to accomplish this.
In addition to simply increasing the width and height of the image, this class should also stretch the original image to fit the new size. This modification should take place in the getPixelColor() method. For example, if the original image has a height and width of 2, and the zoom multiplier is 2, then the decorated image should have a height of 4 and a width of 4, but the underlying pixels should be scaled so that
getPixelColor(0, 0), getPixelColor(0, 1), getPixelColor(1, 0), and getPixelColor(1, 1) all return the same pixel color---that
is, they return the same color as the pixel located at position (0, 0) in the original picture. In other words, each pixel value in the original pixel should be mapped to four pixels in the scaled image.
Putting it all together
Finally, in Main.java, adjust the makeImage() method so that it creates and returns an Image object using the decorator pattern with the following properties:
The base image should be img/kmp.jpg
The red border is color (255, 0, 0) and has a thickness of 5 (before scaling)
The blue border is color (0, 0, 255) and has a thickness of 50 (before scaling)
The yellow circle is color (255, 255, 0), has radius 40 (before scaling), and is at position (50, 50) in the final, unscaled image
The orange square is color (200, 80, 10), has size 40 (before scaling), and is at position (100, 100) in the final, unscaled image After applying these decorators, add one last ZoomDecorator with a multiplier of 2, to make the image bigger
You can see an example of the final image in img/jedi.png.
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