CODEWITHSUNDEEP
java
OmarMjhd
OmarMjhd

Reputation: 13

For loop isn't incrementing Java

So I'm pretty new to Java, and I'm trying to write a for loop to go through all of the pixels in an image, but for some unknown reason, the for loop never increments. When I try to run the code, it prints out the height and the width of the image, that are assigned to the variables "height" and "width" respectively, and then enters the for loops but only prints out 0, and 0 before finishing running.

public class ImageProcessor {
    public static Pic image;
    public static Pic modImage;
    public static int width;
    public static int height;
    public static int average;
    public static Pixel modPixel;

    public static void main(String[] args) {
            Pic image = new Pic(args[0]);
            int width = image.getWidth();
            int height = image.getHeight();
            System.out.println(width);

            System.out.println(height);

            greyscale();
    }

    public static Pic greyscale() {
        for (int w = 0; w <= width; w++) {
            for (int h = 0 ; h <= height; h++) {
                System.out.println(w);
                System.out.println(h);
            } 
        }
        return image;
    } 
}

Upvotes: 0

Views: 168

Answers (4)

Joni
Joni

Reputation: 111389

Your main method declares width and height as local variables, shadowing the static variables with the same names and leaving them set to their default value of 0. Change the code in the main method to:

        width = image.getWidth();
        height = image.getHeight();

Upvotes: 6

Paolo
Paolo

Reputation: 22646

The problem is you are not assigning the getWidth and getHeight result to the static variables at the top.

Because you've written:

int width = ...

it has actually created a new local variable called "width". When the greyscale method is called it has no knowledge of this variable.

If you changed those lines to be:

width = ...

It'll assign it to the static variables.

As a general principle, what would be even better is to avoid passing state around using global (i.e. static) variables at all. Instead give the greyscale method everything it needs when you call it.

public static Pic greyscale(int width, int height)

This means you never have to rely on the outside state of the world being correct when you are in the method, makes reasoning about your program easier and makes it less likely that you'll introduce bugs by altering width/height unexpectedly from other bits of code.

Upvotes: 1

Kayz
Kayz

Reputation: 667

In the main-method remove the int before width and height.

Upvotes: 0

Elliott Frisch
Elliott Frisch

Reputation: 201537

Your main method defines local variables of the same name; they shadow your static width and height fields;

public static int width;  // <-- default to 0.
public static int height; // <-- default to 0.

public static void main(String[] args) {
  Pic image = new Pic(args[0]);
  width = image.getWidth();   // <-- use the static width
  height = image.getHeight(); // <-- use the static height

  System.out.println(width);
  System.out.println(height);
  greyscale();
}

Upvotes: 0

Related Questions