I am learning 'class' now and I came up with a problem in class 'MyPixel', it seems works fine if I just ignore to create the constructor.

Code:

//MyPixel p;
MyScreen s = new MyScreen(600,600);

void setup(){
  size(600,600);
  background(0);
  //p = new MyPixel(10,20,200);

  //p.plot();
  //for(int i = 0; i < s.pixelGrid.length; i++){
  s.plot();
  //}
}

class MyScreen{
  //members
  MyPixel[] pixelGrid;

  //constructor
  MyScreen(int xgrid, int ygrid){
    pixelGrid = new MyPixel[xgrid*ygrid];

    for(int i = 0; i < pixelGrid.length; i++){
      pixelGrid[i] = new MyPixel();
      pixelGrid[i].x = i % xgrid;
      pixelGrid[i].y = i / ygrid; 
      pixelGrid[i].c = color((int)random(255));
    }
  }

  //method
  void plot(){
    for(int i = 0; i < pixelGrid.length; i++){
      pixelGrid[i].plot();
    }    
  }

}

class MyPixel{

  //members
  float x,y;
  color c;
  
  //constructor
  MyPixel(float _x, float _y, color _c){
    x = _x;
    y = _y;
    c = _c;   
  }


  //method
  public void plot(){
    stroke(c);
    //point(x,y);
   ellipse(x, y, 5,5);
  }



} 

Perhaps I'm repeating what PhiLho (why are you squared now?) has already said here...

You call a constructor with no arguments:

Quote:


It would seem that if you don't declare a constructor within your class then a default constructor (that takes no arguments) is enabled.  However, when you do declare a constructor then this default constructor is not enabled; which would be why you've probably been getting an error along the lines of "The constructor ...MyPixel() is undefined".

Since the constructor you've defined takes arguments you must pass these arguments when you call the constructor.  Alternatively you can create multiple constructors for your class that take different sets of arguments:

Code:

class MyPixel{

  //members
  float x,y;
  color c;
  
  //constructor
  // takes no arguments
  MyPixel() {
    // But maybe your object will break if no default values are 
    // set for the object properties...
    // So perhaps set default values for variables here?
  }
  // Takes three arguments...
  MyPixel(float _x, float _y, color _c){
    x = _x;
    y = _y;
    c = _c;   
  }

// ... snip ...
}