Write me a code in the java langauge and the only instance varibale is: 'private char$[][]$ grid;$\text{'}$

public void applyGravity$()$

This method simulates a simple step for gravity pulling tiles down by replacing

each EMPTY cell in grid with the one above it $($and setting the one above to

EMPTY$).$ It starts at the bottom row of grid and processes up to the top. Note:

this replacement cannot happen for the top row of grid since there is not a row

above the top row.