array within an arrayList? - comparing objects - in way over my head!

Programming Questions

adamguk

array within an arrayList? - comparing objects - in way over my head!

in Programming Questions • 9 months ago

Hello, thanks for reading my question!

I am trying to make a patch that interprets the MIDI data I send it into class objects that are then represented visually.

Per MIDI note played, two messages are sent - a note-on and a note-off (both containing channel, pitch and velocity data). I am trying to add a note object to an ArrayList when a note-on message is received and then subsequently, to remove that same object when this note's corresponding note-off message is received. Here is my problem...

Adding note objects to an ArrayList when a note-on message is received doesn't seem to be the problem, the problem is removing the corresponding object. I think I need to compare the note-off message received with the note objects contained in the array list, removing the note object that corresponds - but doing this has proved to be well beyond my programming abilities.

Below is what I have so far, I'd be very grateful for any help you could provide.

Thank you,

Adam

import fullscreen.*;
import themidibus.*; //Import the library
MidiBus busA; //The first MidiBus
import javax.sound.midi.MidiMessage; //Import the MidiMessage classes http://java.sun.com/j2se/1.5.0/docs/api/javax/sound/midi/MidiMessage.html
import javax.sound.midi.SysexMessage;
import javax.sound.midi.ShortMessage;
PVector v1;
FullScreen fs;
void setup() {
size(400,400,P3D);
background(0);
MidiBus.list(); //List all available Midi devices. This will show each device's index and name.
busA = new MidiBus(this, 0, 0);
busA.addInput("IAC Bus 1");
v1 = new PVector (width/2,height/2,0);
// Create the fullscreen object
fs = new FullScreen(this);
// enter fullscreen mode
fs.enter();
}
void draw() {
//lights();
//fill(0,10);
//noStroke();
//rect(0,0,width/2,height/2);
}
void noteOn(int channel, int pitch, int velocity){
//println(channel +" "+ pitch +" "+ velocity);
Note.addANote(channel, pitch, velocity);
}
void noteOff(int channel, int pitch, int velocity){
//println(channel +" "+ pitch +" "+ velocity);
Note.removeANote(channel, pitch, velocity);
}
class Note {
ArrayList notes = new ArrayList();
Note(int channel, int pitch, int velocity){
int[] data = {channel, pitch, velocity};
}
void addANote (int channel, int pitch, int velocity){
notes.add(new Note(channel,pitch,velocity));
}
void removeANote (int channel, int pitch, int velocity){
int _channel = this.channel;
int _pitch = this.pitch;
int _velocity = this.velocity;
int[] _data = {_channel, _pitch, _velocity};
for (int i = 0; i < notes.size(); i++){
if(notes.get[i] == _data){
notes.remove(i);
}
}
}
void display (){
for(int i = 0; i < notes.size(); i++){
}
}
}

Replies(2)

PhiLho

Re: array within an arrayList? - comparing objects - in way over my head!

9 months ago

Your Note class tries to do too much, to hold the data for a note and to hold all notes.
You should only keep the data for a note.
You can make an array list outside of this class, at program level or in a special collection of notes class.
Beside, you should use .equals() to compare notes, not ==
But then, you have to define the equals() method for this class.

GoToLoop

Re: array within an arrayList? - comparing objects - in way over my head!

9 months ago

May I also add the issue of variable scope?
I see that variable data[] is declared/created inside the class constructor.

Problem is, due to how scope works in Java and many other languages,
it ceases to exist once that scope finishes.
In other words, data[] exists only inside constructor Note(),
and its contents are lost once Note() is done!

The right place to declare a variable which is kept alive and is tasked on being used by everyone,
is in the "field" section of a class.

For example, you have declared busA, fs and v1 as fields of the sketch itself.
Thus, those variables can be used across the sketch's domain!

You've also declared variable notes as a field for class Note.
So notes can be freely accessed inside that class,
and even outside using the point operator!

Now another issue -> When you declare/create an ArrayList,
it is extremely advisable to define which type of data it's gonna be stored there.

For that, the angle brackets are used:
List < Note > notes = new ArrayList ();

This way, you don't have to use cast operator to add/get/remove things from there.

And as PhiLho's already mentioned...
You shouldn't create an array to store instances from a class, inside that same class itself!
Place and declare that notes as a field of the sketch instead.