Ok, so I am making this platform game and I have my tilemap, walking and jumping animations. There is, however, one big problem. I am struggling to figure out how to implement collisionDetection. If anyone would like to help me and educate me on how to do this with the code I have, that would be AMAZING! 

Hi ,
 I'm making a 2d sidescroller and my code, at the moment is all over the place. Currently, I am working on trying to get my jump animation to work when pressing the Up Key. I can't get it to animate correctly, and I am pressed for time for this project. I still haven't implemented collisionDetection, and I probably need help on that too. I think one way to do it would be to detect if there is a certain element below the player and if there is, etc..etc..but I can't figure out how to code it correctly if that is the case. If anyone is willing to help me, I would appreciate it. I want to learn, so if my code is extremely off or is terrible, please tell me how to improve it. The code and classes are posted below.
Level1 Class:
 int x,y;
  int frame=0;
  int frameY=0;
  PImage bg;
  TileMap map;
  int scrollNum=0;
  int scrollNumY=0;
  String images[]= {"blank.gif","tree_1.gif","tree_2.gif","tree_3.gif",
  "tree_4.gif","tree_5.gif","tree_6.gif","tree_7.gif","tree_8.gif",
  "tree_9.gif","tree_10.gif","tree_11.gif","tree_12.gif","tree_13.gif",
  "tree_14.gif","tree_15.gif","tree_16.gif","tree_17.gif","tree_18.gif",
  "tree_19.gif","tree_20.gif","tree_21.gif","tree_22.gif","tree_23.gif",
  "tree_24.gif","tree_25.gif","tree_26.gif","tree_27.gif","tree_28.gif",
  "tree_29.gif","Platform1.png","platform2.png","platform3.png",
  "tree_bush.gif","rock 1.png","rock2.png","rock3.png","rock6.png",
  "bridge_1.png","bridge_2.png","bridge_3.png"};
 
  boolean hScroll = true;
  boolean hScrollL= true;
  boolean vScroll=true;
  boolean vScrollU=true;
  int xPos;
  int yPos;
  float spriteX=32;
  float spriteY=170;
  Mandrill mandrill;
  boolean walkRight=false;
  boolean walkLeft=false;
  boolean jumpRight= false;
  boolean jumpLeft=false;
  boolean fallRight=false;
  boolean fallLeft=false;
 boolean isFacingRight=true;
 boolean isFacingLeft=false;
  void setup()
  {
    size(550,440);
    map= new TileMap(100,20);
    frameRate(5);
    bg=loadImage("level_1_background.png");
  
    for(int i=0;i<100;i++)
    {
      for(int j=0;j<20;j++)
      {
        int imageIndex= tile_map[j][i];
        String imageName=images[imageIndex];
        map.setTile(loadImage(imageName),j,i);
      }
    }
   
    mandrill= new Mandrill(spriteX,spriteY);
  }

void draw()
{
  frame= constrain(frame,0,bg.width-width);
  frameY= constrain(frameY,0,bg.height-height);
  set(-frame,0,bg);
 
  for(int i=0; i< map.getHeight();i++)
  {
    for(int j=0;j< map.getWidth();j++)
    {
          image(map.getTile(j,i),(32*j)-scrollNum,(32*i)-scrollNumY);
          xPos=(32*j)-scrollNum;
          yPos=(32*i)-scrollNumY;
   
    }
  }
  
  if(walkRight==true)
  {
    mandrill.walkRight(spriteX,spriteY);
   
  }
  else if( walkLeft==true)
  {
      mandrill.walkLeft(spriteX,spriteY);
     
  }
  else if(jumpRight==true)
  {
        mandrill.jumpRight(spriteX,spriteY);
  }
  else  if(jumpLeft==true)
  {
        mandrill.jumpLeft(spriteX,spriteY);
  }
  else
  {
    if(isFacingRight==true)
       mandrill.drawRight(spriteX,spriteY);
     if(isFacingLeft==true)
       mandrill.drawLeft(spriteX,spriteY);
  }
 

   
  if(xPos <= 516) hScroll = false;
  else hScroll = true;
 
  if(xPos >=3200) hScrollL=false;
  else hScrollL=true;
  if(yPos>=734) vScroll=false;
  else vScroll=true;
  if(yPos <=410) vScrollU=false;
  else vScrollU=true;
 
 
}


void keyPressed (KeyEvent e)
{
  int key=e.getKeyCode();
  switch(key)
  {
     case 37: //left
      if(hScrollL==false)
        scrollNum+=0;
      else
      {
        if(spriteX<100)
        {
          scrollNum-=14;
          frame--;
        }
        walkLeft=true;
        spriteX-=6;
      }
      break;
   case 39: //right
      if(hScroll == false)
      {
        scrollNum-=0;
      }
      else
      {
        if(spriteX>width/2)
        {
          scrollNum+=14;
          frame++;
        }
      
        walkRight=true;
        spriteX+=6;
      
      }
      break;
  
   case 38: //up
       //if(spriteY<height/2)
       //{
         //scrollNumY-=14;
       //}
        jumpRight=true;
       spriteY-=2;
       spriteX++;
      
        
       break;
  case 40:
      if(vScrollU==false)
        scrollNumY-=0;
      else
      {
        scrollNumY+=6;
      }
  }  
}

void keyReleased(KeyEvent e)
{
  int key= e.getKeyCode();
  switch(key)
  {
    case 37:
      walkLeft=false;
      isFacingRight=false;
      isFacingLeft=true;
     
      break;
    case 39: 
      walkRight=false;
      isFacingRight=true;
      isFacingLeft=false;
      break;
    case 38:
      //scrollNum+=1;
     
      jumpRight=false;
     
      break;
    case 40:
   
  }
}

int[][]tile_map={
   {0,0,0,0,0,0,0,0,0,0,0,0,1,2,3,4,5,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,
   2,3,4,5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,6,7,8,9,10,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,6,7,
   8,9,10,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,11,12,13,14,
   15,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,11,12,13,14,15,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,31,31,31,31,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,16,17,18,19,
   20,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,16,17,18,19,20,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,33,0,0,
   0,0,0,0,0,31,31,31,35,35,35,35,33,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,0,0,21,22,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,21,22,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,30,31,32,0,0,0,0,
   30,31,31,31,31,31,31,31,31,31,32,0,0,
   0,0,0,0,0,0,0,0,0,0,33,33,0,0,0,0,0,
   0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,0,23,24,25,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   23,24,25,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,31,0,34,36,37,0,0,0,0,34,
   35,35,35,35,35,35,35,35,35,37,0,0,0,
   0,0,0,0,0,0,0,0,31,31,31,31,31,31,31,
   31,32,0
   },
   {0,0,0,0,0,0,0,33,33,0,0,33,0,26,27,28,
   29,33,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,26,27,28,29,33,0,0,0,0,0,0,0,33,33,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   34,35,35,35,35,35,35,35,37,0,0,0,0,0,0,
   0,0,0,0,0,0,35,35,35,35,35,35,35,35,37,
   0
   },
   {0,30,31,31,31,31,31,31,31,31,31,31,31,
   31,31,31,31,31,32,0,0,0,0,0,30,31,31,
   31,31,31,31,31,31,31,31,31,31,31,31,31,
   31,31,31,31,31,31,31,31,31,31,31,31,0,
   0,0,0,31,31,32,0,0,0,0,0,0,0,0,0,0,0,
   34,35,35,35,36,36,37,0,0,0,0,0,0,0,0,
   0,33,33,0,0,35,35,35,35,35,35,35,37,0,
   0
   },
   {0,34,35,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,35,37,0,0,0,0,0,34,35,35,
   35,35,35,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,35,35,35,35,35,35,35,35,0,
   0,0,0,35,35,37,0,30,31,32,0,0,0,0,0,0,
   0,0,36,36,36,0,0,0,0,0,0,0,0,0,0,31,
   31,31,31,31,31,31,31,32,36,36,36,36,0,
   0,0
   },
   {0,0,34,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,37,0,0,0,30,32,0,0,34,35,
   35,35,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,35,35,35,35,35,35,35,35,
   35,31,31,31,31,35,37,0,0,35,35,35,32,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,35,35,35,35,35,35,35,35,37,0,0,
   0,0,0,0,0
   },
   {0,0,0,34,36,36,36,35,35,35,36,36,36,
   36,36,36,37,0,0,0,0,36,36,0,0,0,34,
   35,35,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,35,37,0,0,0,35,35,35,35,
   31,32,0,0,0,0,38,39,39,39,39,40,0,0,
   0,0,0,0,0,33,35,35,35,35,35,35,35,37,
   0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,36,36,36,0,0,0,0,0,0,0,
   33,0,0,0,0,0,0,0,0,0,34,36,34,35,35,
   35,35,35,35,35,35,35,35,35,35,35,35,
   35,35,35,35,35,35,35,35,35,35,35,37,
   0,0,0,0,34,35,35,35,35,35,31,31,31,
   31,0,0,0,0,0,0,31,31,31,31,31,31,31,
   31,32,36,35,35,36,36,36,0,0,0,0,0,0,
   0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,30,
   31,32,0,0,0,0,0,0,0,0,0,0,34,36,36,36,
   36,36,36,36,36,36,36,36,36,36,36,36,
   36,36,36,36,36,36,36,36,37,0,0,0,0,0,
   0,34,35,35,35,35,35,35,35,35,0,0,0,0,
   0,0,34,35,35,35,35,35,35,35,37,0,36,
   36,0,0,0,0,0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,36,
   36,36,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,36,36,35,35,35,35,35,
   36,0,0,0,0,0,0,0,34,35,35,35,35,
   35,37,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,30,31,31,32,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,34,36,36,36,
   37,0,0,0,0,0,0,0,0,0,36,36,36,36,
   36,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,35,35,35,35,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,33,33,0,0,0,0,
   0,0,33,30,31,35,35,35,35,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,30,31,31,31,31,
   31,31,31,31,31,31,31,31,31,31,31,31,
   32,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0
   },
   {0,0,0,0,0,0,0,0,0,0,34,35,35,35,35,
   35,35,35,35,35,35,35,35,35,35,35,35,
   37,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0
   },
   {0,0,0,0,0,0,0,0,0,0,0,34,35,35,35,
   35,35,35,35,35,35,35,35,35,35,35,37,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,0
   }
   };
   
TileMap Class:

class TileMap
{
    public int width, height;
    PImage[][] tiles;
 
    TileMap(int x, int y)
    {
        this.width = x;
        this.height = y;
 
        tiles = new PImage[y][x];
    }
 
    int getWidth()
    {
        return width;
    }
 
    int getHeight()
    {
        return height;
    }
 
    void setTile(PImage image, int x, int y)
    {
        tiles[x][y] = image;
    }
 
    PImage getTile(int x, int y)
    {
        if(x < 0 || x > width || y < 0 || y > height)
        {
            println("Tile doesn't exist");
            return null;
        }
        else
        {
            return tiles[y][x];
        }
    }
}

Player Class (a Mandrill):

class Mandrill
{
  float xPos;
  float yPos;
  PImage mandrill;
  PImage mandrill1;
  int frame;
  float gravity=-9.5;
  Mandrill(float x,float y)
  {
    xPos=x;
    yPos=y;
   
    mandrill=loadImage("mandrill_walk0.gif");
    mandrill1=loadImage("mandrill_walk_left0.gif");
  }
 
  void drawRight(float x,float y)
  {
    image(mandrill,x, y);
  }
 
  void drawLeft(float x,float y)
  {
    image(mandrill1,x,y);
  }
 
  void setXPos(float x)
  {
    xPos=x;
  }
  void setYPos(float y)
  {
    yPos=y;
  }

 
  float getXPos()
  {
    return xPos;
  }
 
  float getYPos()
  {
    return yPos;
  }
 
  void walkRight(float x,float y)
  {
    PImage[] images= new PImage[4];
    for (int i = 0; i < 4; i++)
    {
      String filename = "mandrill_walk" + i + ".gif";
      images[i] = loadImage(filename);
    }
    frameRate(8);
    frame = (frame+1) % 4;
    image(images[frame], x, y);
  }
 
  void walkLeft(float x, float y)
  {
    PImage[] images= new PImage[4];
    for (int i = 0; i < 4; i++)
    {
      String filename = "mandrill_walk_left" + i + ".gif";
      images[i] = loadImage(filename);
    }
    frameRate(8);
    frame = (frame+1) % 4;
    image(images[frame], x, y);
  }
 
  void jumpRight(float x, float y)
  {
    PImage[] images= new PImage[6];
    for (int i = 0; i < 6; i++)
    {
      String filename = "mandrill_jump" + i + ".gif";
      images[i] = loadImage(filename);
    }
    frameRate(8);
    frame=(frame+1) % 4;
    image(images[frame], x, y);
  }
 
 
 
  void jumpLeft(float x, float y)
  {
    PImage[] images= new PImage[6];
    for (int i = 0; i < 6; i++)
    {
      String filename = "mandrill_jump_left" + i + ".gif";
      images[i] = loadImage(filename);
     }
    frameRate(5);
    frame = (frame+1) % 4;
    image(images[frame], x, y);
  }
 
 
 
}