Grid.java

import java.util.*;

/**
 * {@code Grid} instances represent the grid in <i>The Game of Life</i>.
 */
public class Grid implements Iterable<Cell> {

    private final int numberOfRows;
    private final int numberOfColumns;
    private final Cell[][] cells;

    /**
     * Creates a new {@code Grid} instance given the number of rows and columns.
     *
     * @param numberOfRows    the number of rows
     * @param numberOfColumns the number of columns
     * @throws IllegalArgumentException if {@code numberOfRows} or {@code numberOfColumns} are
     *                                  less than or equal to 0
     */
    public Grid(int numberOfRows, int numberOfColumns) {
        this.numberOfRows = numberOfRows;
        this.numberOfColumns = numberOfColumns;
        this.cells = createCells();
    }

    @Override
    public Iterator<Cell> iterator() {
        return new GridIterator(this);
    }

    private Cell[][] createCells() {
        Cell[][] cells = new Cell[getNumberOfRows()][getNumberOfColumns()];
        for (int rowIndex = 0; rowIndex < getNumberOfRows(); rowIndex++) {
            for (int columnIndex = 0; columnIndex < getNumberOfColumns(); columnIndex++) {
                cells[rowIndex][columnIndex] = new Cell();
            }
        }
        return cells;
    }

    /**
     * Returns the {@link Cell} at the given index.
     *
     * <p>Note that the index is wrapped around so that a {@link Cell} is always returned.
     *
     * @param rowIndex    the row index of the {@link Cell}
     * @param columnIndex the column index of the {@link Cell}
     * @return the {@link Cell} at the given row and column index
     */
    public Cell getCell(int rowIndex, int columnIndex) {
        return cells[getWrappedRowIndex(rowIndex)][getWrappedColumnIndex(columnIndex)];
    }

    private int getWrappedRowIndex(int rowIndex) {
        return (rowIndex + getNumberOfRows()) % getNumberOfRows();
    }

    private int getWrappedColumnIndex(int columnIndex) {
        return (columnIndex + getNumberOfColumns()) % getNumberOfColumns();
    }

    /**
     * Returns the number of rows in this {@code Grid}.
     *
     * @return the number of rows in this {@code Grid}
     */
    public int getNumberOfRows() {
        return numberOfRows;
    }

    /**
     * Returns the number of columns in this {@code Grid}.
     *
     * @return the number of columns in this {@code Grid}
     */
    public int getNumberOfColumns() {
        return numberOfColumns;
    }

    /**
     * Transitions all {@link Cell}s in this {@code Grid} to the next generation.
     *
     * <p>The following rules are applied:
     * <ul>
     * <li>Any live {@link Cell} with fewer than two live neighbours dies, i.e. underpopulation.</li>
     * <li>Any live {@link Cell} with two or three live neighbours lives on to the next
     * generation.</li>
     * <li>Any live {@link Cell} with more than three live neighbours dies, i.e. overpopulation.</li>
     * <li>Any dead {@link Cell} with exactly three live neighbours becomes a live cell, i.e.
     * reproduction.</li>
     * </ul>
     */
    void nextGeneration() {
        goToNextState(calculateNextStates());
    }

    private boolean[][] calculateNextStates() {
        boolean[][] states = new boolean[getNumberOfRows()][getNumberOfColumns()];
            for (int i = 0; i < getNumberOfRows(); i++) {
                for (int j = 0; j < getNumberOfColumns(); j++) {
                    states[i][j] = calculateNextState(i, j, getCell(i, j));
                }
            }
        return states;
    }

    private boolean calculateNextState(int rowIndex, int columnIndex, Cell cell) {
        int aliveNeighbours = countAliveNeighbours(rowIndex, columnIndex);
        if (cell.isAlive()) {
            return aliveNeighbours > 1 && aliveNeighbours < 4;
        }
        return aliveNeighbours == 3;
    }

    private int countAliveNeighbours(int rowIndex, int columnIndex) {
        int aliveNeighbours = 0;
        List<Cell> cells = getNeighbours(rowIndex, columnIndex);
        for (Cell cell : cells) {
            if (cell.isAlive())
                aliveNeighbours++;
        }
        return aliveNeighbours;
    }


    private List<Cell> getNeighbours(int rowIndex, int columnIndex) {
        List<Cell> cells = new ArrayList<>();
        for (int i =  rowIndex - 1; i <= rowIndex + 1; i++) {
            for (int j = columnIndex - 1; j <= columnIndex + 1; j++) {
                if (i != rowIndex && j != columnIndex || i > 0 && j > 0 && i < getNumberOfRows() && j < getNumberOfColumns())
                    cells.add(getCell(i, j));
            }
        }
	return cells;
    }

    private void goToNextState(boolean[][] nextState) {
        for (int i = 0; i < getNumberOfRows(); i++) {
            for (int j = 0; j < getNumberOfColumns(); j++) {
                if (nextState[i][j])
                    getCell(i, j).setAlive();
                else
                    getCell(i, j).setDead();
            }
        }
    }

    /**
     * Sets all {@link Cell}s in this {@code Grid} as dead.
     */
    void clear() {
        GridIterator iterator = new GridIterator(this);
        while (iterator.hasNext()) {
            iterator.next().setDead();
        }
    }

    /**
     * Goes through each {@link Cell} in this {@code Grid} and randomly sets it as alive or dead.
     *
     * @param random {@link Random} instance used to decide if each {@link Cell} is alive or dead
     * @throws NullPointerException if {@code random} is {@code null}
     */
 
    void randomGeneration(Random random) {
    }

}