Processing sketch for a music player

AudioPlayer.java

/*
A Processing sketch for an audio player with frequency visualization.

Authors:  Prithvijit Chakrabarty (prithvichakra@gmail.com)
          Kartik Lovekar (kslovekar@gmail.com)
*/
import ddf.minim.*;
import java.io.*;
import java.util.*;

Minim minim;
ddf.minim.AudioPlayer song;
AudioMetaData meta;
Play playButton;
Rewind rewind;
Forward ffwd;
long startTime = 0;
long endTime = 0;
ArrayList<String> filePaths = new ArrayList<String>(); 
boolean play = false;
int num = 0;
int numFiles = 0;
float position;

void setup()
{
  size(500,500);
  final File folder = new File("M:\\Music\\Sample Music\\MUSIC\\Queens of the Stone Age");
  getFilePaths(folder);
  playButton = new Play((width-width/25)/2, height-height/5, width/25, height/50);
  rewind = new Rewind(width/2 - 71, height-height/5, width/25, height/50);
  ffwd = new Forward(width/2 + 50, height-height/5, width/25, height/50);
  minim = new Minim(this);
  startTime = System.currentTimeMillis();
  loadSong();
}

void draw()
{
  background(0);
  
  playButton.update();
  playButton.draw();
  rewind.update();
  rewind.draw();
  ffwd.update(); 
  ffwd.draw();
  
  if(play == true)
    text("Now Playing: "+meta.author()+" - "+meta.title(),8,15);
  else
    text("Paused: "+meta.author()+" - "+meta.title(),8,15);
  fill(255);
  
  stroke(255);
  line(0, 8*height/9, width, 8*height/9);
  
  // sDrawing the waveform
  for(int i = 0; i < song.bufferSize()-1; i++)
  {
    float x1 = map(i, 0, song.bufferSize(), 0, width);
    float x2 = map(i+1, 0, song.bufferSize(), 0, width);
    line(x1, height/5 + song.left.get(i)*height/10, x2, height/5 + song.left.get(i+1)*height/10);
    line(x1, 2*height/5 + song.right.get(i)*height/10, x2, 2*height/5 + song.right.get(i+1)*height/10);
  }
  
  // Mapping position of the seek circle to song length
  position = map(song.position(), 0, song.length(), 0, width);
  ellipse(position, 8*height/9, 15, 15);
  fill(255);
  
  if(play == true)
    endTime = System.currentTimeMillis();
  // check if current track is over to load next track
  if(endTime - startTime >= song.length() && !song.isPlaying() && play == true)
  {
    num++;
    loadSong();
    song.play();
    play = true;
  }
}

void keyPressed()
{
  if(key == 'p')
  {
    if(!play)
    {
      song.play();
      play = true;
      //println(play);
     }
    else
    {
      song.pause();
      play = false;
      //println(play);
    }
  }
  if(key == 'n') // to load next track
  {
    song.pause(); // pause current track 
    num++;
    play = true;
    loadSong();
    song.play();
    
  }
  if(key == 'b') // to load previous track
  {
    song.pause(); // pause current track
    num--;
    play = true;
    loadSong();
    song.play();
  }
}

// Fast forwards or rewinds when mouse is pressed
void mousePressed()
{
  playButton.mousePressed();
  rewind.mousePressed();
  ffwd.mousePressed();
}

void mouseReleased()
{
  playButton.mouseReleased();
  rewind.mouseReleased();
  ffwd.mouseReleased();
}

// loading file paths from specified directory
void getFilePaths(final File folder) 
{
  for(final File fileEntry : folder.listFiles())
  {
    if(fileEntry.isDirectory())
      getFilePaths(fileEntry);
    else
    {
      String path = fileEntry.getPath();
      if(path.substring(path.length()-3,path.length()).equals("mp3"))
      {  
        filePaths.add(path);
        numFiles++;
      }
    }
  }
}

void loadSong()
{
  if(num == numFiles) // going back to the first track
    num = 0;
  if(num == -1) 
    num = 0;
  startTime = System.currentTimeMillis();
  song = minim.loadFile(filePaths.get(num));
  meta = song.getMetaData();
  position = map(song.position(), 0, song.length(), 0, width);
}

Button.java

/*
Custom button classes

Authors:  Prithvijit Chakrabarty (prithvichakra@gmail.com)
          Kartik Lovekar (kslovekar@gmail.com)
*/
abstract class Button
{
  int x, y, hw, hh;
  
  Button(int x, int y, int hw, int hh)
  {
    this.x = x;
    this.y = y;
    this.hw = hw;
    this.hh = hh;
  }
  
  boolean pressed()
  {
    return mouseX > x - hw && mouseX < x + hw && mouseY > y - hh && mouseY < y + hh;
  }
  
  abstract void mousePressed();
  abstract void mouseReleased();
  abstract void update();
  abstract void draw();
}

class Play extends Button
{
  boolean play;
  boolean invert;
  
  Play(int x, int y, int hw, int hh) 
  { 
    super(x, y, hw, hh); 
    play = true;
  }
  
  // code to handle playing and pausing the file
  void mousePressed()
  {
    if ( pressed() )
    {
      invert = true;
      if ( song.isPlaying() ) 
      {
        song.pause();
        play = true;
      }
      else
      {
        song.play();
        play = false;
      }
    }
  }
  
  void mouseReleased()
  {
    invert = false;
  }
  
  // play is a boolean value used to determine what to draw on the button
  void update()
  {
    if ( song.isPlaying() ) play = false;
    else play = true;
  }
  
  void draw()
  {
    if ( invert )
    {
      fill(255);
      stroke(0);
    }
    else
    {
      noFill();
      stroke(255);
    }
    rect(x - hw, y - hh, hw*2, hh*2);
    if ( invert )
    {
      fill(0);
      stroke(255);
    }
    else
    {
      fill(255);
      noStroke();
    }
    if ( play )
    {
      triangle(x - hw/3, y - hh/2, x - hw/3, y + hh/2, x + hw/2, y);
    }
    else
    {
      rect(x - hw/3, y - hh/2, hw/4, hh);
      rect(x + hw/8, y - hh/2, hw/4, hh);
    }
  }
}

class Rewind extends Button
{
  boolean invert;
  boolean pressed;
  
  Rewind(int x, int y, int hw, int hh)
  {
    super(x, y, hw, hh);
    invert = false;
  }
  
  // code used to scrub backward in the file
  void update()
  {
    // if the rewind button is currently being pressed
    if (pressed)
    {
      // get the current song position
      int pos = song.position();
      // if it greater than 255 milliseconds
      if ( pos > 255 )
      {
        // rewind the song by 255 milliseconds
        song.skip(-255);
      }
      else
      {
        // if the song hasn't played more than 100 milliseconds
        // just rewind to the beginning
        song.rewind();
      }
    }
  }
  
  void mousePressed()
  {
    pressed = pressed();
    if ( pressed ) 
    {
      invert = true;
      // if the song isn't currently playing, rewind it to the beginning
      if ( !song.isPlaying() ) song.rewind();      
    }
  }
  
  void mouseReleased()
  {
    pressed = false;
    invert = false;
  }

  void draw()
  {
    if ( invert )
    {
      fill(255);
      stroke(0);
    }
    else
    {
      noFill();
      stroke(255);
    }
    rect(x - hw, y - hh, hw*2, hh*2);
    if ( invert )
    {
      fill(0);
      stroke(255);
    }
    else
    {
      fill(255);
      noStroke();
    }
    triangle(x - hw/2, y, x, y - hh/2, x, y + hh/2);
    triangle(x, y, x + hw/2, y - hh/2, x + hw/2, y + hh/2);    
  }  
}

class Forward extends Button
{
  boolean invert;
  boolean pressed;
  
  Forward(int x, int y, int hw, int hh)
  {
    super(x, y, hw, hh);
    invert = false;
  }
  
  void update()
  {
    // if the forward button is currently being pressed
    if (pressed)
    {
      // get the current position of the song
      int pos = song.position();
      // if the song's position is more than 40 milliseconds from the end of the song
      if ( pos < song.length() - 40 )
      {
        // forward the song by 40 milliseconds
        song.skip(40);
      }
      else
      {
        // otherwise, cue the song at the end of the song
        song.cue( song.length() );
      }
      // start the song playing
      song.play();
    }
  }
  
  void mousePressed()
  {
    pressed = pressed();
    if ( pressed ) 
    {
      invert = true;      
    }
  }
  
  void mouseReleased()
  {
    pressed = false;
    invert = false;
  }

  void draw()
  {
    if ( invert )
    {
      fill(255);
      stroke(0);
    }
    else
    {
      noFill();
      stroke(255);
    }
    rect(x - hw, y - hh, hw*2, hh*2);
    if ( invert )
    {
      fill(0);
      stroke(255);
    }
    else
    {
      fill(255);
      noStroke();
    }
    triangle(x, y, x - hw/2, y - hh/2, x - hw/2, y + hh/2);
    triangle(x, y - hh/2, x, y + hh/2, x + hw/2, y);    
  }  
}