Mr. Nom Invades Android - Beginning Android Games - page 258

Next, we define a list called parts that holds all the parts of Mr. Nom. The first item in that list is
the head, and the other items are the tail parts. The second member of the Snake class holds the
direction in which Mr. Nom is currently heading.
public Snake() {
direction = UP ;
parts.add( new SnakePart(5, 6));
parts.add( new SnakePart(5, 7));
parts.add( new SnakePart(5, 8));
}
In the constructor, we set up Mr. Nom to be composed of his head and two additional tail parts,
positioned more or less in the middle of the world, as shown previously in Figure 6-6 . We also
set the direction to Snake.UP , so that Mr. Nom will advance upward by one cell the next time he's
asked to advance.
public void turnLeft() {
direction += 1;
if if(direction > RIGHT )
direction = UP ;
}
public void turnRight() {
direction - = 1;
if if(direction < UP )
direction = RIGHT ;
}
The methods turnLeft() and turnRight() just modify the direction member of the Snake class.
For a turn left, we increment it by one, and for a turn right, we decrement it by one. We also have
to make sure that we wrap Mr. Nom around if the direction value gets outside the range of the
constants we defined earlier.
public void eat() {
SnakePart end = parts.get(parts.size()-1);
parts.add( new SnakePart(end.x, end.y));
}
Next up is the eat() method. All it does is add a new SnakePart to the end of the list. This new
part will have the same position as the current end part. The next time Mr. Nom advances, those
two overlapping parts will move apart, as discussed earlier.
public void advance() {
SnakePart head = parts.get(0);
int len = parts.size() - 1;
for ( int i = len; i > 0; i--) {
SnakePart before = parts.get(i-1);
SnakePart part = parts.get(i);
part.x = before.x;
part.y = before.y;
}