Help with java (2 simple classes)

Question

would anyone be able to help me with some questions about two very short java classes?
i have come up with some answers of my own, but yeah, i'm not sure how correct my answers are....
the 4 questions are:
1. The data attributes m, n and grid in the HeatGrid class are declared private, and methods
such as gridHeight(), gridWidth() and copyGrid() are provided to extract their value. Why
is the better class design than simply declaring those attributes as public?
My answer: So other classes accessing them cannot modify those data atributes, i am not sure why this is better class design.
2. Why must the (global) constants in HeatSim.java be declared static ?
My Answer: because HeatSim is what you run first and so you don't create a HeatSim object, you just access its methods, thus the need to make them static.
3. Assuming HeatGrid has been fully implemented, during the execution of the statement
HeatGrid = new HeatGrid(inGridFile), how many objects of HeatGrid, double [][] and
Scanner are created?
My Answer: 1 HeatGrid object, 1 doulbe[][] object and 1 scanner object
Which of these objects must still exist after the statement completes execution?
4. For each of the classes HeatSim and HeatGrid, identify the client and supplier classes
(including library classes).
My Answer: So far this is what i have done. for the HeatSim class, i said that the supplier classea are:
double
int
boolean
String
Math Class
viewgrid class
array
and the clients for the HeatSim class are:
HeatGrid class
if anyone can help me i will but up the VERY short code to these two classes. I am really stuck and any help woould be greatly appriciated! :)
Lots o love
Sarah

Answer 1

ok here is the code (i don't have my compelted copy on me but this will do for the moment).....
import java.lang.Integer;
import java.lang.Double;
import java.text.DecimalFormat;
public class HeatSim {
    final static boolean ENABLE_VIEW = true; // if true, create GUI to view grid
    final static double DEFAULT_THR = 1.0e-02;
    final static int DEFAULT_PAUSE = 100; // pause between each update of window in ms
    final static int DISPLAY_WIDTH = 7;   // width to print each grid value
    final static int MAX_MN_DISPLAY = 10; // maximum grid size to be displayed
    public static void main(String[] args) {
        // initialize program `parameters' according to the command line,
        // entering `default' values if none were given
        String inGridFile = (args.length < 1)? "": args[0];
        int nIter = (args.length < 2)? 1: Integer.parseInt(args[1]);
        double Thr = (args.length < 3)? DEFAULT_THR: Double.parseDouble(args[2]);
        String dumpFile = (args.length < 4)? "": args[3];
     DecimalFormat residFormat = new DecimalFormat("0.00E0");
        ViewGrid view = null;
        System.out.println("HeatFlow simulation program");
        if (inGridFile.equals("")) {
            System.out.println("Error: an empty grid file name was entered");
            return;
        // create HeatGrid object
        HeatGrid heatGrid = new HeatGrid(inGridFile);
        int m = heatGrid.gridHeight();
        int n = heatGrid.gridWidth();
        if (m <= MAX_MN_DISPLAY  && n <= MAX_MN_DISPLAY) {
            System.out.println("\nGrid at time 0:" );
            heatGrid.display(DISPLAY_WIDTH);
        if (ENABLE_VIEW) {
            // create a ViewGrid WINDOW object to view the grid
            view = new ViewGrid(m+2, n+2, DEFAULT_PAUSE);
            view.display(heatGrid.time(), 0.0, heatGrid.copyGrid());
        while (heatGrid.time() != nIter && heatGrid.residual() > Thr) {
            heatGrid.iterate();
            if (m <= MAX_MN_DISPLAY  && n <= MAX_MN_DISPLAY) {
                System.out.println("Grid at time " + heatGrid.time() +
                                " has residual " +
                     residFormat.format(heatGrid.residual()));
                heatGrid.display(DISPLAY_WIDTH);
            if (ENABLE_VIEW) {
                 view.display(heatGrid.time(), heatGrid.residual(),
                              heatGrid.copyGrid());
        } //while(...)
        if (ENABLE_VIEW) {
            view.finalize();
        if (!dumpFile.equals("")) {
         heatGrid.dumpGrid(dumpFile);
        System.out.println("\nHeat Flow simulation of (" + m + "+2)x(" + n +
                           "+2) grid ends at time " +  heatGrid.time() +
                           " with residual " +
                  residFormat.format(heatGrid.residual()));
    } //mainProgram()
} //HeatSim
import java.util.Scanner;
import java.io.*;
import java.text.DecimalFormat;
public class HeatGrid {
    private int m, n;
    private double[][] grid;     // m+2 x n+2 array representing a grid
    private int t;               // the time the grid has been evolved
    private double resid;        // residual left from the last timestep
    // initializes m, n and grid according to the information in the grid file
    // of name gridFileN; sets t to 0, and resid to Double.MAX_VALUE
    public HeatGrid(String gridFileN) {
    } //HeatGrid()
    // returns the value of m
    public int gridHeight() {
        return 0;         // [ replace with an appropriate value ]
    } //gridHeight()
    // returns the value of n
    public int gridWidth() {
        return 0;         // [ replace with an appropriate value ] =
    } //gridWidth()
    // returns the value of t
    public int time() {
        return 0;         // [ replace with an appropriate value ]
    } //time()
    // returns the value of the residual from the previous timestep
    public double residual() {
        return 0;         // [ replace with an appropriate value ]
    } //residual()
    // returns a copy of the grid
    public double[][] copyGrid() {
        return null;         // [ replace with an appropriate value ]
    } //copyGrid
    // precondition: all elements of grid can be printed to 1 decimal place
    // using width characters.
    // prints the m+2 x n+2 grid by rows, rows in descending order.
    // All values are printed to 1 decimal place, and are right-justified
    // in a text field of width characters.
    // Note: this method is for debugging; hence right-justification is useful
    public void display(int width) {
    } //display()
    // advance the simulation a single timestep
    public void iterate() {
     } //iterate()
    // prints the m+2 x n+2 grid by rows, rows in ascending order.
    // All values are printed to 2 decimal places, with at least one space
    // between them.
    // Note: this method is intended for result checking by a computer program;
    // thus justification is not important.
    public void dumpGrid(String outGridFileN) {
    } //dumpGrid