Question

The two-dimensional array of boolean values that will be referenced by matrix will be used to simulate an LED-based display that can hold LETTERS_PER_DISPLAY letters.

Modify the constructor to create a two-dimensional array of boolean that has FONT_LETTER_HEIGHT rows and (FONT_LETTER_WIDTH times LETTERS_PER_DISPLAY) columns and assign it to the instance variable matrix.

public class LEDDisplay
{
   private boolean[] = matrix;
   private static final int FONT_LETTER_HEIGHT = 5;
   private static final int FONT_LETTER_WIDTH = 6;
   private static final int LETTERS_PER_DISPLAY = 10;

public LEDDisplay()
{
    boolean[][] matrix = new boolean[FONT_LETTER_HEIGHT][FONT_LETTER_WIDTH]
}

Please could you tell me whether my constructor is correct?

Answer 1

it’s actually not correct – you hide the member variable matrix by defining a local to the constructor one. Here is the correct way:

public class LEDDisplay
{
   private boolean[][] matrix;
   private static final int FONT_LETTER_HEIGHT = 5;
   private static final int FONT_LETTER_WIDTH = 6;
   private static final int LETTERS_PER_DISPLAY = 10;

public LEDDisplay()
{
    matrix = new boolean[FONT_LETTER_HEIGHT][FONT_LETTER_WIDTH * LETTERS_PER_DISPLAY];
}