cc150_5_8.java

public class Q5_8 {
    public void drawHLine(byte[] screen, int width, int x1, int x2, int y) {
    	int height = screen.length / (width / 8);
    	if(y < 0 || y >= height || x1<0 || x2 <0 || x1 > screen.length * 8 || x2 > screen.length * 8)
    	{
    		return;
    	}
    	
    	int idx = y*(width/8);
    	int idx1 = idx + (x1/8);
    	int idx2 = idx + (x2/8);
    	
    	for (int i = idx1+1; i< idx2; i++){
    		screen[i] = (byte)0xFF;
    	}
    	
    	// mask for the start offset, before the start offset set 0, after is 1
    	byte mask1 = (byte) (0xff >>> x1 % 8); //>>> no sign shift right
    	// mask for the end offset, after the end offset set 0, before 1
    	byte mask2 = (byte) (~((1 << (7 - x2 % 8)) - 1));
    	
    	
        if (idx1 == idx2) {
            screen[idx1] |= (mask1 & mask2);
        } else {
            screen[idx1] |= mask1;
            screen[idx2] |= mask2;
        }
    }
	
	
	
    public static void main(String[] args) {
        Q5_8 q5_8 = new Q5_8();
        byte[] screen = new byte[48];
        int width = 8;
        for (int i = 0; i < screen.length / width; ++i) {
            for (int j = 0; j < width; ++j) {
                System.out.print(screen[i * width + j]);
            }
            System.out.println();
        }
        
        System.out.println();

        q5_8.drawHLine(screen, width * 8, 9, 26, 1);
        for (int i = 0; i < screen.length / width; ++i) {
            for (int j = 0; j < width; ++j) {
                System.out.print(screen[i * width + j]);
            }
            System.out.println();
        }
        
        System.out.println();
        screen = new byte[12];
        q5_8.drawHLine(screen, width * 8, 1, 5, 0);
        for (int i = 0; i < screen.length / width; ++i) {
            for (int j = 0; j < width; ++j) {
                System.out.print(screen[i * width + j]);
            }
            System.out.println();
        }
    }
}