How to make a 'zoom' function display squares outside of bounds in a 2D character array

Question

Basically, I have to implement a variety of methods to mess around with a two-dimensional character array for a class (display, recolour, and zoom). I've got everything to work except for one problem- the 'zoom' function is meant to display the selected character and all character directly around it, but displaying an empty space wherever there isn't anything to display. However I cannot figure out how to make it do this (currently it just displays an error message if I try and 'zoom' into any character around the edge of the array.

Code below, I gutted everything not relevant and left only the display (d) and zoom (z) functions. To be clear, the problem is not in entering the initial co-ordinates out of bounds there's actually another method to handle that that I removed, the problem is in 'zooming' into a space around the edge of the array, which will return an error message as it tries to display out of bounds spaces.

Code:

import java.util.Scanner;

public class CharMapFORHELP {
    public static void zoom(char[][] map, int row, int col) {
        //the problem method
        System.out.print(map[row - 1][col - 1]);
        System.out.print(map[row - 1][col]);
        System.out.print(map[row - 1][col + 1]);
        System.out.println();
        System.out.print(map[row][col - 1]);
        System.out.print(map[row][col]);
        System.out.print(map[row][col + 1]);
        System.out.println();
        System.out.print(map[row + 1][col - 1]);
        System.out.print(map[row + 1][col]);
        System.out.print(map[row + 1][col + 1]);
        System.out.println(); //adds the newline
    }

    /**
     * Displays the given character-based map
     * with a leading and trailing blank line.
     */
    public static void displayMap(char[][] map) {
        for (int row = 0; row < map.length; row++) {
            for (int col = 0; col < map[row].length; col++) {
                System.out.print(map[row][col] + " ");
            }
            System.out.println(); //adds the newline
        }
    }

    // code to convert String array into map. Truthfully
    // I don't 100% understand whats going on here, this
    // was provided to us already written.
    public static char[][] stringToArray(String str) {
        char[][] result;
        String[] rows;

        rows = str.split("\n");
        result = new char[rows.length][];
        for (int r = 0; r < rows.length; r++) {
            result[r] = rows[r].toCharArray();
        }
        return result;
    }

    public static void main(String[] args) {
        //Commands
        final char CMD_DISPLAY = 'd', CMD_ZOOM = 'z', CMD_QUIT = 'q';
        Scanner sc = new Scanner(System.in);
        char[][] map; // the character-based map
        char command; // user's entered command
        int row;      // |
        int col;      // |- command parameters
        char fill;    // |
        String strMap = "####################\n" +
                        "####           #####\n" +
                        "#                 ##\n" +
                        "##           ###  ##\n" +
                        "######       #######\n" +
                        "##                ##\n" +
                        "####    ##    ##  ##\n" +
                        "######  ######### ##\n" +
                        "####################";

        map = stringToArray(strMap);
        System.out.println("Char Map");
        System.out.println("========");
        System.out.println();
        System.out.println("Enter commands (? for help)." +
                " There are no further prompts after this point.");

        do {
            //read the next single-character command
            command = sc.next().charAt(0);
            switch (command) {
                case CMD_DISPLAY:
                    displayMap(map);
                    break;
                case CMD_ZOOM:
                    row = sc.nextInt();
                    col = sc.nextInt();
                    zoom(map, row, col);
                    break;
                case CMD_QUIT:
                    break;
            }
        } while (command != CMD_QUIT);
    }
}

Answer 1

One way would be to check if the array index will be out of bounds, and then print a different character.

Wa can make this easy by creating a new method to check if the character is out of bounds:

public static String getValue(char[][] map, int row, int col){
    //Check the row
    if (row >= 0 && row < map.length){
        //Check the col
        if(col >= 0 && col < map[row].length){
            //Return the character only if the row and col are valid
            return map[row][col];
        }
    }

    //If the above checks fail then the index is out of bounds.
    //So return a placeholder for printing, in this example we use a dash
    return "-";
}

Now we can modify the zoom method to use the getValue(map, row, col) method like this:

public static void zoom(char[][] map, int row, int col) {    
    System.out.print(getValue(map, row - 1, col - 1));
    System.out.print(getValue(map, row - 1, col));
    System.out.print(getValue(map, row - 1, col + 1));
    System.out.println();
    System.out.print(getValue(map, row, col - 1));
    System.out.print(getValue(map, row, col));
    System.out.print(getValue(map, row, col + 1));
    System.out.println();
    System.out.print(getValue(map, row + 1, col - 1));
    System.out.print(getValue(map, row + 1, col));
    System.out.print(getValue(map, row + 1, col + 1));
    System.out.println(); //adds the newline
}