ArrayList of different classes using Object

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justinyang

ArrayList of different classes using Object

in Programming Questions • 3 years ago

Hi List,

Something I've been wanting to do for a while is to be able to dynamically populate an ArrayList with instances of different classes and then use these class instances. For example, here I create two different classes. Each class has a method named drawClass(). I hope to be able to pull instances out of an ArrayList, no matter what the class, and run drawClass(), as long as a method with that name exists in the class:

ArrayList test;
ArrayList classes;
void setup() {
size(500,500);
test = new ArrayList();
test.add(new HLine(100.0, 5));
test.add(new testEllipse());
}
void draw() {
background(0);
for(int i=test.size()-1; i>=0; i--) {
Object objectToDraw = (Object) test.get(i);
//one thought
objectToDraw.drawClass();
//another
objectToDraw.getClass() objectToDraw2 = (objectToDraw.getClass()) test.get(i);
objectToDraw2.drawClass();
}
}
}
class HLine {
float ypos, speed;
HLine (float y, float s) {
ypos = y;
speed = s;
}
void drawClass() {
ypos += speed;
if (ypos > width) {
ypos = 0;
}
stroke(255,0,0);
line(0, ypos, width, ypos);
}
}
class testEllipse {
void drawClass() {
fill(0,0,255);
ellipse( 200,200,100,100);
}
}

Another related question is, is there a method in Processing/Java where you can get a list of all of the classes/class methods/class variables within a sketch? I would guess oscPlug perhaps engages something like this to automatically pass on osc commands to methods within classes.

Thanks,

Justin

Replies(4)

PhiLho

Re: ArrayList of different classes using Object

3 years ago

I don't really understand the last question. At least, its purpose. You probably can do that with reflection, but there might be better methods, depending on what you want to do.

For the first question, the answer is: interfaces (the Java kind).
You define an interface with the drawClass method in it, and you make your classes implementing this method. Then you make an ArrayList of this interface, and you are good to go.
Mock code:

interface CanDraw { void draw(); }
ArrayList<CanDraw> thingsThatCanDraw = new ArrayList<CanDraw>();
class HLine() { HLine() { ... } void draw() { line( ... ); } }
class LongRect { LongRect() { ... } void draw() { rect( ... ); } }
// In setup or elsewhere
thingsThatCanDraw.add(new HLine( ... ));
thingsThatCanDraw.add(new LongRect( ... ));
void draw()
{
for (CanDraw thing : thingsThatCanDraw)
{
thing.draw();
}
}

The interface guarantees that objects implementing it will have the desired method in them, whatever their exact nature.

justinyang

Re: ArrayList of different classes using Object

3 years ago

Thanks for this answer! exactly what I'm looking for.

As regards to the second question. I am in the habit of OSCifying my sketches, ie /shape x, y, width, height; /shapeClr FFFFFFFF ... and I generally use oscPlug for this. As some of my sketches end up having many classes with loads of osc addressable variables it would be nifty to have my sketch automatically spit out all of the classes and methods and variables in a ascii or xml or some other such format and then generate a list of osc messages based on this list.

How it relates to the above question is that I thought one workaround would be to take a list of all classes and do a compare if Object.getClass() == 'one of the classes in my sketch' then run the method on that sketch. but your solution is tidier thanks.

justinyang

Re: ArrayList of different classes using Object

3 years ago

Also, I'm not sure I understand what the <> notation means as in below <CanDraw>. Does this mean that my ArrayList thingsThatCanDraw now can only contain objects of CanDraw class/interface? Thanks.

ArrayList<CanDraw> thingsThatCanDraw = new ArrayList<CanDraw>();

kooogy

Re: Re: ArrayList of different classes using Object

3 years ago

yep, that's java generics, new as of 1.5 and lets you specify the object type during the declaration which allows stronger type checking and means you don't need to cast the results when you extract them. only available in processing 1.2.1 though.

http://download.oracle.com/javase/1.5.0/docs/guide/language/generics.html

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