Falling Sand Project: Part $1-$ Run the Program

Run the program in NetBeans. You should see a window pop up$.$ On the left side is a black rectangular canvas which will soon be inhabited by particles. On the right side there is one button for each tool you will be able to paint with: Empty $($for erasing$)$ and Metal $($for creating metal particles$).$ You can't actually paint now, because you haven't written the code yet.

Look in the SandLab.java file, and you'll see that a SandLab remembers two things:

grid $-$ a $2-$dimensional array of int values that represent the type of particle found at each location

display $-$ the SandDisplay used to show the particles on the screen

Notice that we're using int values to represent particle types, with $0$ representing empty, $1$ representing metal, and higher values representing the additional particle types you'll be adding. To avoid confusion, we never want to see these particle type numbers $(0,1,$ etc.$)$ in our code! Instead, we've declared variables for each of these types. You'll see these listed near the top of SandLab.java.

public static final int EMPTY $=0$;

public static final int METAL $=1$;

This lets us use meaningful variable names instead of confusing type numbers in our code. For example:

if $($type $==$ METAL$)$

These variables are marked final to indicate that they are constants. $($Attempts to re$-$assign to these variables will not compile.$)$ By convention in Java, we use all$-$caps names for constants. $($Traditionally$,$ constants are also declared as public and static, so that we can access them from outside the file by writing SandLab.METAL, for example.$)$

Part $2-$ Constructor

The SandLab constructor $($lines $23-30)$ already initializes the display field to refer to a new SandDisplay with appropriate dimensions and tool names. Insert code to initialize the grid field to refer to a $2-$dimensional array of the same dimensions. The rows are the first dimension of the array, and the columns are the second dimension. $($You won't be able to test this code yet.$)$

Part $3-$ locationClicked Method

The locationClicked method is called $($by the run method$)$ whenever the user clicks on some part of the canvas. The selected tool $($empty$,$ metal, etc.$)$ is passed to the method. Store this value in the corresponding position of the grid array. $($You won't be able to test this code yet.$)$

package fallingsand;

import java.awt.$*$;

public class SandLab

$\{$

$//$add constants for particle types here

public static final int EMPTY $=0$;

public static final int METAL $=1$;

$//$do not add any more fields

private int$[][]$ grid;

private SandDisplay display;

public static final int ROWS $=120$;

public static final int COLUMNS $=80$;

public static void main$($String$[]$ args$)$

$\{$

SandLab lab $=$ new SandLab$($ROWS$,$ COLUMNS$)$;

lab.run$()$;

$\}$

public SandLab$($int numRows, int numCols$)$

$\{$

String$[]$ names;

names $=$ new String$[2]$;

names$[$EMPTY$]=$ "Empty";

names$[$METAL$]=$ "Metal";

display $=$ new SandDisplay$("$Falling Sand", numRows, numCols, names$)$;

$\}$

$//$called when the user clicks on a location using the given tool

private void locationClicked$($int row, int col, int tool$)$

$\{$

$\}$

$//$copies each element of grid into the display

public void updateDisplay$()$

$\{$

Color empty $=$ new Color$(0,0,0)$;

for $($int row $=0$; row $<$ ROWS; row$++)$

$\{$

for $($int column $=0$; column $<$ COLUMNS; column$++)$

$\{$

if $($grid$[$row$][$column$]==$ EMPTY$)$

$\{$

display.setColor$($row$,$ column, empty$)$;

$\}$

$\}$

$\}$

$\}$

$//$called repeatedly.

$//$causes one random particle to maybe do something.

public void step$()$

$\{$

$\}$

$//$do not modify

public void run$()$

$\{$

while $($true$)$

$\{$

for $($int i $=0$; i $<$ display.getSpeed$()$; i$++)$

$\{$

step$()$;

$\}$

updateDisplay$()$;

display.repaint$()$;

display.pause$(1)$; $//$wait for redrawing and for mouse

int$[]$ mouseLoc $=$ display.getMouseLocation$()$;

if $($mouseLoc $!=$ null$)//$test if mouse clicked

$\{$

locationClicked$($mouseLoc$[0],$ mouseLoc$[1],$ display.getTool$())$;

$\}$

$\}$

$\}$

$\}$