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I will discuss this program in fragments. A complete listing of the program is provided in Listing 8 near the end of the module.
The driver class named Prob01
The driver class containing the main method is shown in Listing 1 .
| Listing 1 . The driver class named Prob01. |
|---|
public class Prob01{
public static void main(String[]args){
Picture pic = new Prob01Runner().run();System.out.println(pic);
}//end main method}//end class Prob01 |
There is nothing in Listing 1 that I haven't explained in earlier modules.
The println statement in Listing 1 causes the second line of text to be displayed in Figure 3 .
The constructor for the class named Prob01Runner
The constructor for the class named Prob01Runner is shown in Listing 2 .
| Listing 2 . The constructor for the class named Prob01Runner . |
|---|
class Prob01Runner{
public Prob01Runner(){System.out.println("Display your name here.");
}//end constructor |
The code in Listing 2 simply causes the first line of text in Figure 3 to be displayed on the command line screen.
Beginning of the method named run
The code in the driver class in Listing 1 instantiates a new object of the Prob01Runner class and immediately calls the run method belonging to that object. The run method begins in Listing 3 .
| Listing 3 . Beginning of the method named run. |
|---|
public Picture run(){
Picture pix = new Picture("Prob01.jpg");//Display the input picture.pix.explore();
//Call the mirrorUpperQuads method to modify the top// half of the picture.
pix = mirrorUpperQuads(pix); |
A new Picture object
Listing 3 instantiates a new Picture object from an image file and saves a reference to that object in the local variablenamed pix .
Display the Picture object
Then Listing 3 calls the explore method on the reference producing the output image shown in Figure 1 .
Modify top half of the picture
Finally, Listing 3 calls the method named mirrorUpperQuads to mirror the upper-left quadrant of the picture into the upper-right quadrant. A copy of a reference to the picture object is passed tothe method and the value returned by the method is saved in the variable named pix . ( I will have more to say about this later.)
Put the explanation of the run method on hold
I will put the explanation of the run method on hold temporarily and explain the method named mirrorUpperQuads .
Beginning of the mirrorUpperQuads method
The beginning of the mirrorUpperQuads method is shown in Listing 4 .
| Listing 4 . Beginning of the mirrorUpperQuads method. |
|---|
private Picture mirrorUpperQuads(Picture pix){
Pixel leftPixel = null;Pixel rightPixel = null;int midpoint = pix.getWidth()/2;
int width = pix.getWidth(); |
Note that the method receives a copy of a reference to the picture.
Declare working variables
The code in Listing 4 begins by declaring a pair of local working variables of type Pixel . These variables will be used to hold information about individual pixels.
Compute width and midpoint of the image
Then Listing 4 computes and saves the width and the horizontal midpoint of the image.
Mirror pixel colors around the midpoint
Listing 5 uses a pair of nested for loops to copy the pixel colors on the left of the midpoint to corresponding mirror-image pixels on the right sideof the midpoint.
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