Grid.java

import java.util.List;

public class Grid {

    private int rows;
    private int columns;
    private char[][] map;

    // Constructor
    public Grid(int rows, int columns) {
        this.rows = rows;
        this.columns = columns;
        this.map = new char[rows][columns];

        initializeMap();
    }

    // Initialize the grid
    private void initializeMap() {

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < columns; j++) {
                map[i][j] = '.';
            }
        }

        // Start
        map[0][0] = 'S';

        // Goal
        map[9][9] = 'G';
    }

    // Display normal grid
    public void display() {

        System.out.println();

        for (int i = 0; i < rows; i++) {

            for (int j = 0; j < columns; j++) {
                System.out.print(map[i][j] + " ");
            }

            System.out.println();
        }

        System.out.println();
    }

    // Check whether position is inside grid
    public boolean isValidPosition(int row, int column) {

        return row >= 0 &&
               row < rows &&
               column >= 0 &&
               column < columns;
    }

    // Check obstacle
    public boolean isObstacle(int row, int column) {

        return map[row][column] == '#';
    }

    // Add obstacle
    public boolean setObstacle(int row, int column) {

        if (!isValidPosition(row, column)) {
            return false;
        }

        // Don't allow obstacle on Start or Goal
        if (map[row][column] == 'S' ||
            map[row][column] == 'G') {
            return false;
        }

        map[row][column] = '#';

        return true;
    }

    // Display calculated A* path
    public void displayPath(List<Node> path) {

        System.out.println();

        // Create a copy of the original map
        char[][] pathMap = new char[rows][columns];

        for (int i = 0; i < rows; i++) {

            for (int j = 0; j < columns; j++) {
                pathMap[i][j] = map[i][j];
            }
        }

        // Put * on calculated path
        for (Node node : path) {

            if (pathMap[node.row][node.column] == '.') {
                pathMap[node.row][node.column] = '*';
            }
        }

        // Print calculated path
        for (int i = 0; i < rows; i++) {

            for (int j = 0; j < columns; j++) {
                System.out.print(pathMap[i][j] + " ");
            }

            System.out.println();
        }

        System.out.println();
    }
}