Snake.java

import java.util.Vector;

public class Snake {

        private Vector<Coord> positions;  // this vector stores all of the coordinates
                                          // that currently contain a snake part
        private int dir;                  // 0- up, 1- right, 2- down, 3- left

        // Constructor

        public Snake(Coord startCoordinate) {
            dir = 0;
            positions = new Vector<Coord>();
            positions.add(below(below(startCoordinate)));
            positions.add(below(startCoordinate));
            positions.add(startCoordinate);
        }


        // Accessors

        public Coord head() {
            return positions.firstElement();  // returns first item in positions vector
        }

        public Coord tail() {
            return positions.lastElement();  // returns last item in positions vector
        }

        public int direction() {
            return dir;
        }


        // Movement

        public void move() {
            Coord newPos = head();

            // calculate which coordinate changes
            if(dir == 0) {
                newPos.y = head().y -1;
            } else if(dir == 1) {
                newPos.x = head().x +1;
            } else if(dir == 2) {
                newPos.y = head().y +1;
            } else if(dir == 3) {
                newPos.x = head().x -1;
            }

            positions.add(0, newPos);  // add new head coordinate
            positions.remove(positions.lastElement());  // remove tail coordinate
        }


        // Directions

        public void left() {
            dir = 3;
        }

        public void right() {
            dir = 1;
        }

        public void up() {
            dir = 0;
        }

        public void down() {
            dir = 2;
        }


        // Helpers

        // ensures rotations wrap around
        public void normalize() {
            if(dir > 3)
                dir = 0;
            if(dir < 0)
                dir = 3;
        }

        // returns coordinate below input
        public Coord below(Coord input) {
            return new Coord(input.x, input.y++);
        }
}