Completing all methods of Grid.java

Grid.java

-import java.util.Arrays;
-import java.util.Iterator;
-import java.util.List;
-import java.util.Random;
+import java.util.*;
 
 /**
  * {@code Grid} instances represent the grid in <i>The Game of Life</i>.
@@ -98,29 +95,73 @@ public class Grid implements Iterable<Cell> {
     }
 
     private boolean[][] calculateNextStates() {
-        return null;
+        boolean [][] state = new boolean[numberOfRows][numberOfColumns];
+        for (int i = 0; i < state.length; i++) {
+            for (int j = 0; j < state[i].length; j++) {
+                if (calculateNextState(i, j, cells[i][j] ))
+                    state[i][j] = true;
+                else
+                    state[i][j] = false;
+            }
+        }
+    return state;
     }
 
     private boolean calculateNextState(int rowIndex, int columnIndex, Cell cell) {
+        int aliveNeighbours = countAliveNeighbours(rowIndex, columnIndex);
+        if (cell.isDead() && aliveNeighbours == 3)
+            return true;
+        if (cell.isAlive() && aliveNeighbours == 2 || aliveNeighbours == 3)
+            return true;
+        else
             return false;
     }
 
     private int countAliveNeighbours(int rowIndex, int columnIndex) {
-        return 0;
+        int aliveNeighbours = 0;
+        for (int i = 0; i < getNeighbours(rowIndex, columnIndex).size(); i++) {
+            Cell cell = getNeighbours(rowIndex, columnIndex).get(i);
+            boolean cellState = cell.isAlive();
+            if (cellState)
+                aliveNeighbours++;
+        }
+        return aliveNeighbours;
     }
 
 
     private List<Cell> getNeighbours(int rowIndex, int columnIndex) {
-	return null;
+	    List<Cell> neighbours = new ArrayList<>();
+	    neighbours.add(getCell(rowIndex, columnIndex + 1));
+        neighbours.add(getCell(rowIndex + 1, columnIndex + 1));
+        neighbours.add(getCell(rowIndex + 1, columnIndex));
+        neighbours.add(getCell(rowIndex + 1, columnIndex -1));
+        neighbours.add(getCell(rowIndex, columnIndex - 1));
+        neighbours.add(getCell(rowIndex - 1, columnIndex - 1));
+        neighbours.add(getCell(rowIndex - 1, columnIndex));
+        neighbours.add(getCell(rowIndex - 1, columnIndex + 1));
+        return neighbours;
     }
 
     private void goToNextState(boolean[][] nextState) {
+        for (int i = 0; i < nextState.length; i++) {
+            for (int j = 0; j < nextState[i].length; 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() {
+        boolean [][] clearState = new boolean[numberOfRows][numberOfColumns];
+        for (int i = 0; i < clearState.length; i++) {
+            Arrays.fill(clearState[i], false);
+        }
+        goToNextState(clearState);
     }
 
     /**
@@ -131,6 +172,10 @@ public class Grid implements Iterable<Cell> {
      */
  
     void randomGeneration(Random random) {
+        boolean [][] randomState = new boolean[getNumberOfRows()][getNumberOfColumns()];
+        for (int i = 0; i < randomState.length; i++) {
+            Arrays.fill(randomState[i], random.nextBoolean());
+        }
+        goToNextState(randomState);
     }
-
 }
\ No newline at end of file