康威的生命游戏

Question

My question is boolean isLive = false; why is this assigned as false? I have seen very similer examples but I never quet understand it. could anyone explain what this line is doing?

/**
 * Method that counts the number of live cells around a specified cell

 * @param board 2D array of booleans representing the live and dead cells

 * @param row The specific row of the cell in question

 * @param col The specific col of the cell in question

 * @returns The number of live cells around the cell in question

 */

public static int countNeighbours(boolean[][] board, int row, int col)
{
    int count = 0;

    for (int i = row-1; i <= row+1; i++) {
        for (int j = col-1; j <= col+1; j++) {

            // Check all cells around (not including) row and col
            if (i != row || j != col) {
                if (checkIfLive(board, i, j) == LIVE) {
                    count++;
                }
            }
        }
    }

    return count;
}

/**
 * Returns if a given cell is live or dead and checks whether it is on the board
 * 
 * @param board 2D array of booleans representing the live and dead cells
 * @param row The specific row of the cell in question
 * @param col The specific col of the cell in question
 * 
 * @returns Returns true if the specified cell is true and on the board, otherwise false
 */
private static boolean checkIfLive (boolean[][] board, int row, int col) {
    boolean isLive = false;

    int lastRow = board.length-1;
    int lastCol = board[0].length-1;

    if ((row >= 0 && row <= lastRow) && (col >= 0 && col <= lastCol)) {             
        isLive = board[row][col];
    }

    return isLive;
}

Answer 1

That's simply the default value, which may be changed if the test ( if clause) is verified.

It defines the convention that cells outside the board aren't live.

This could have been written as :

private static boolean checkIfLive (boolean[][] board, int row, int col) {

    int lastRow = board.length-1;
    int lastCol = board[0].length-1;

    if ((row >= 0 && row <= lastRow) && (col >= 0 && col <= lastCol)) {             
        return board[row][col];
    } else {
        return false;
    }
}

Answer 2

First we assign boolean value as 'false' (ensuring default condition)
Then if valid condition is found we change the value, else default false will be returned.

Answer 3

boolean isLive = false;

This is the default value of a boolean variable. If you declare as an instance variable it is automatically initialized to false.

why is this assigned as false?

Well, we do this, just to start with a default value, then we can change later on to true value, based on certain condition.

if ((row >= 0 && row <= lastRow) && (col >= 0 && col <= lastCol)) {             
    isLive = board[row][col];
}
return isLive;

So, in above code, if your if condition is false, then it is similar to returning a false value. Because, the variable isLive is not changed.

But if your condition is true, then the return value will depend upon the value of board[row][col] . If it is false , return value will still be false , else true .

Answer 4

boolean isLive = false;

It is a default value assigned to the boolean variable.

Just like:

int num = 0;