arraylist

Programming Questions

pacoruizg..

in Programming Questions • 1 year ago

Hi,

An array list is a resizable list ob objects. I´ve used it sometimes but now I simply need a resizable list of variables. In this case of colors, and it doesnt work. It doesnt seem to me that the solution is to make a class of colors. I thougt that I could use an arraylist of colors and it doesnt work. This is the line of the errror:

colors.add (new color (c));

This is the complete code, trying to get a color palette from a picture

class ColorHandler {
color[] palette ;
ColorHandler(){
}
void SetColor(PImage theimage){
    color c;
    boolean found;
    ArrayList colors = new ArrayList ();
    for (int i = 0; i < theimage.width; i++){
      for (int j = 0; j < theimage. height; j++){
        c= theimage.get(i,j);
        found = FALSE;
        for ( k = 0; k < colors.size; k++){
          color thecolor = (color) colors.get(k);
          if (thecolor == c){
            found = TRUE;
          }
        }
        if (!found){
              colors.add (new color (c));
        }

      }
    }
}
}

Replies(9)

PhiLho

Re: arraylist

1 year ago

Well, I think you never saw a "new color()" line in Processing...
color type in Processing is a bit special: it is not a class, so color instances are not objects. They are int values, actually, created with the #AABBCC syntax or the color() function.

Actually, when you run a Processing sketch, it first run a pre-compiling phase where it converts a number of things. Among them, color declarations are just replaced by int declarations. You can see the result of such pre-processing in the .java file(s) generated when you export a sketch.

Back to your code, why do you do a new color(c) since c is already a color?

Note that if your code is to get a list of unique colors in an image, your code is rather inefficient. You better use a different Java collection class: HashSet.
If you search the forum (from Processing.org) for HashSet, you will see examples of usage of this class.

pacoruizg..

Re: arraylist

1 year ago

Well, I think you never saw a "new color()" line in Processing...

So simply it cant be used? Arraylist is only for objects not for variables? Not for colors?

Back to your code, why do you do a new color(c) since c is already a color?

Because c is the value for the new color. In another example that does work:

balls.add ( new ball(mouseX,mouseY));

mouseX, mouseY are the values for creating a new ball, same as c is the value for creating a new color of the arraylist.

I'll use HashSet and change the code, but even inefficient, can my code work? Just for understand it and have my ideas clear.

HashSet has to be a set of objects? It can´t be a set of variables? A set of colors? For example, this code doesnt work:

HashSet <color> palette = new HashSet <color>();

quarks

Re: arraylist

1 year ago

Points to note
(1) ArrayList can only hold objects and objects are created from classes

(2) In Processing color is an alias for int so
      color c;
      is the exactly the same as
      int c;

(3) Since int is not a class then neither is color

(4) On most computers the color of a pixel is represented by a 32 bit integer (8 alpha; 8 red; 8 green; 8 blue)

(5) In Processing the function color(parameters) is used to calculate and return the 32 integer value that can be used to colour a pixel based on the parameter values passed.

In Java int, float, double, boolean are known as primitive data types and are not classes, but Java does provide matching classes for these - Integer, Float, Double, Boolean (ALL Java classes start with an uppercase letter). It means that you could use Integer instead of int for your collection.

The following sketch will load an image, create a HashSet<Integer> to hold unique values of the pixel colour, then convert it to an Integer array which is then sorted. The sorted array is then used to display the palette under the image the result looks like this.

PImage picture;
Integer[] palette;
void setup(){
size(466, 520);
background(0);
picture = loadImage("kadinsky.jpeg");
image(picture,0,0);
palette = getPalette(picture);
for(int i = 0; i < palette.length; i++){
set(i % width, 330 + (i / width), palette[i]);
}
fill(255);
text("Number of pixels in image = " + picture.width * picture.height, 10, height - 40);
text("Number of unique colours = " + palette.length, 10, height - 20);
}
Integer[] getPalette(PImage img){
HashSet<Integer> colours = new HashSet<Integer>();
img.loadPixels();
for(int p : img.pixels){
colours.add(new Integer(p));
}
Integer[] p = colours.toArray(new Integer[colours.size()]);
Arrays.sort(p);
return p;
}

PhiLho

Re: arraylist

1 year ago

Your way of mixing quotes and answers without distinguishing them visually is disturbing...

" So simply it cant be used?"
Not for color type. As I wrote, you don't create color objects, because they are not objects, you create colors with color().

" Arraylist is only for objects not for variables?"
Yes and no. Yes, ArrayList is only for objects. No, "variables" makes no sense here. Perhaps you mean "primitive values". Variables are these identifiers allowing to name values, whose values can be objects or primitives.

" Not for colors?"
You can put color values in an ArrayList. Not in an efficient way, but that's not really important.

" Because c is the value for the new color."
Precisely. It is already a color, so no need to create yet another one.
In your new ball(), you create a new object and put it in the array list in the same sentence, but these can be done separately: you can put already existing objects in array lists, you can create new objects without putting them in an array list.

" same as c is the value for creating a new color of the arraylist"
As said, you don't have a ball with mouseX, mouseY, so you need to create a new one, but you have already a color, so no need for a new one.

" can my code work?"
Yes, and actually it can be fast enough, even if inefficient. I just pointed out the HashSet to broaden your knowledge...

Some improvements:

void SetColor(PImage theimage){
ArrayList<color> colors = new ArrayList<color>(); // Declare the type to avoid a cast
for (int i = 0; i < theimage.width; i++) {
for (int j = 0; j < theimage. height; j++) {
color c = theimage.get(i,j); // Could have used pixels[] there
boolean found = false;
for (int k = 0; k < colors.size(); k++) {
color thecolor = colors.get(k);
if (thecolor == c) {
found = true; // Lowercase!
break; // No need to search further
}
}
// Or just use found = colors.contains(c); instead of the above loop
if (!found) {
colors.add(c);
}
}
}
}

Note that at the end of the function, you just loose the ArrayList you created. Perhaps you want to return it?

Note also that color is actually automatically wrapped in an object when putting it in the array list.

kooogy

Re: arraylist

1 year ago

i think you have a bigger problem in your code in that the scope of your ArrayList is limited to the SetColor method and can't be accessed from outside (both PhiLho and quarks fixed this in their code without pointing out the mistake (oh, PhiLho does))

void SetColor(PImage theimage){
color c;
boolean found;
ArrayList colors = new ArrayList ();
...

pacoruizg..

Re: Re: arraylist

1 year ago

So is:

4. public ArrayList colors = new ArrayList ();

isnt it?

PhiLho

Re: arraylist

1 year ago

No, declare colors at the global level, before setup().
And try the syntax I gave (with <color>), it is convenient!

calsign

Re: Re: arraylist

1 year ago

ArrayList can only be typed with an object, so you're going to run into difficulties there... color ( int) is primitive!

PhiLho

Re: arraylist

1 year ago

Ah, so much for me, sometime I should test the code I give!

And looking back at the original code, my advice isn't good either, that's a class method, so the declaration shouldn't be at the global level but should be beside the declaration of the palette. Or, it should remain local, and the palette variable should be created in the same method.

OK, now I tested (quickly) the code:

void setup()
{
PImage img = loadImage("G:/Images/map.png");
ColorHandler ch = new ColorHandler();
ch.SetColor(img);
println(ch.palette);
}
class ColorHandler {
color[] palette ;
ColorHandler(){
}
void SetColor(PImage theimage){
ArrayList<Integer> colors = new ArrayList<Integer>(); // Declare the type to avoid a cast
for (int i = 0; i < theimage.width; i++) {
for (int j = 0; j < theimage. height; j++) {
color c = theimage.get(i,j); // Could have used pixels[] there
boolean found = false;
for (int k = 0; k < colors.size(); k++) {
color thecolor = colors.get(k);
if (thecolor == c) {
found = true; // Lowercase!
break; // No need to search further
}
}
// Or just use found = colors.contains(c); instead of the above loop
if (!found) {
colors.add(c);
}
}
}
int s = colors.size();
palette = new color[s]; // Declare an array, not a new object!
for (int i = 0; i < s; i++) {
color c = colors.get(i);
palette[i] = c;
}
}
}

Note I made an ArrayList of Integer (the object wrapping int), and Java automatically converts int to Integer and back. It is called auto-(un)boxing.

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