Java: random tetris block generated after clear line

I am trying to make a Tetris game in java.

I realized where:

• a new block is created when it hits the floor or its y + 1 is not zero (which means that there is another block below it)

  public void collisionCheck(int x, int y) {
      if (activetile.getY() == this.height-2 || getTileAt(x, y+1) != null) {
          activetile = new Tile(this, 0, 0);    
     }
  }
  

• The line is cleared when the bottom line is filled with non-zero values, or Tetris fragments (for y = 4 (gender), go through x to x = 4 and check if not all are)

  public void checkBottomFull(int x, int y) {
  while (getTileAt(x,y) != null) {    
      say("(" + x + ", " + y +")");
      if (x == 3) {
          say("row is full");     
          //replace full row with tiles from above
          for (int i = 0; i < 4; i++) {
              for (int j = 5; j > 0; j--) {
                  grid[j][i] = getTileAt(i,j-1);
                  grid[j-1][i] = null;
              }
          }
      break;
      }       
     x++;
    }
  }
  

Now I use the keys to move the block:

public void keyPressed(KeyEvent e) {
    int keyCode = e.getKeyCode();
    if(keyCode == KeyEvent.VK_DOWN) {
        activetile.setLocation(activetile.getX(), activetile.getY()+1);
        System.out.println("coordinates: " + activetile.getX() + ", " + activetile.getY());

        collisionCheck(activetile.getX(),activetile.getY());

        checkBottomFull(0,4);

        repaint();
    }
  }

There are two problems that I am having:

1) In the picture you will notice that I completely threw the block to the floor ... and the line cleared. After its removal, it will generate a block in the upper left corner (x = 0, y = 1), which I do not control.

2) , , ..., , , JFrame... , .

FYI: , [j] [i] (, [i] [j]), grid = new Tile[height][width];

?

!