Making sleep work right

[Yakg]

Hey everyone,
I'm making a snake game and so far made all the classes and some functionality, however as of now I'm trying to solve a movement issue I've got..
As you may know from the classic game, the move should be swirling like a snake.. I have built the algorithm which is basically arraylist of snakeLinks to combine a whole snake.
I made it that upon a direction change, it should make the changes in the positions so every link would get the position of the next link after it (kind of)..
I believe the movement is working but I just want to slow down the process so the animation would show..
This is the first time I am trying to embed a thread with sleep and have tried putting it at different places in the code which has failed to work..
It is presented at the moment in the move method in Snake class..
I'm attaching the files, I know it's allot but just hoping some enlightenment with the sleep function to do what I want.

Main:

package Snake;

import java.awt.event.KeyEvent;

public class GUI {

	public static void main(String[] args) {
        Snake snake = new Snake(0.030);
        snake.addLink();
        snake.addLink();
        //snake.addLink();
        Apple apple = new Apple(1.0,0.030);
        while(true){
        	snake.drawSnake();
    		apple.drawApple(!snakeTouchesApple(snake,apple));
        	snake.keyMapper();
        	snake.move();
        	StdDraw.show(80);
        	StdDraw.clear(StdDraw.GRAY);
        }
	}
	
	public static boolean snakeTouchesApple(Snake snake,Apple apple){
		if(Math.abs(snake.getSnake().get(0).getDx()-apple.getxPos())<=0.060 &&//pxsize
				Math.abs(snake.getSnake().get(0).getDy()-apple.getyPos())<=0.060){//pxsize
			apple.placeApple(1.0, 0.030);
			snake.addLink();
			return true;
		}
		return false;
	}
}

Snake:

package Snake;

import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.Random;

public class Snake {
	
	private ArrayList <SnakeLink> snake; 
	private double pxSize;
	private double distance;
	private static int linkNum;
	
	public Snake(double pxSize){
		snake = new ArrayList<SnakeLink>(3);
		snake.add(new SnakeLink());//pxsize(0.030 * 4 
		snake.add(new SnakeLink());//pxsize(0.030 * 2
		snake.add(new SnakeLink());////pxsize(0.0
		this.pxSize = pxSize;
		linkNum=3;
		snake.get(0).setDx(0.120);
		snake.get(1).setDx(0.060);
		snake.get(2).setDx(0.0);
		this.distance=0.060;//pxsize*2
	}
	
	public void addLink(){
		double lastDx = snake.get(linkNum-1).getDx();
		double lastDy = snake.get(linkNum-1).getDy();
		System.out.println("lastDx "+lastDx+" lastDy "+lastDy);
		String dir = snake.get(linkNum-1).getHeaded();
		SnakeLink newLink = new SnakeLink();
		switch (dir){
		case "RIGHT":
			newLink.setDx(lastDx-0.060);//distance!
			break;
		case "LEFT":
			newLink.setDx(lastDx+0.060);//distance!
			break;
		case "UP":
			newLink.setDy(lastDy-0.060);//distance!
			break;
		case "DOWN":
			newLink.setDy(lastDy+0.060);//distance!
			break;
		}
		snake.add(linkNum,newLink);
		linkNum++;
	}
	
	public void drawSnake(){
		for(int i=0; i<linkNum; i++){
			double x = snake.get(i).getDx();
			double y = snake.get(i).getDy();
			StdDraw.filledSquare(x, y, pxSize);
			
		}
	}
	
	//movement section
	public void keyMapper(){
    	//directing the key press to changeDirection if indeed changed
		if(StdDraw.isKeyPressed(KeyEvent.VK_UP) && snake.get(0).getHeaded()!="DOWN")changeDirection("UP");else
			if(StdDraw.isKeyPressed(KeyEvent.VK_DOWN) && snake.get(0).getHeaded()!="UP")changeDirection("DOWN");else
				if(StdDraw.isKeyPressed(KeyEvent.VK_RIGHT) && snake.get(0).getHeaded()!="LEFT")changeDirection("RIGHT");else
					if(StdDraw.isKeyPressed(KeyEvent.VK_LEFT) && snake.get(0).getHeaded()!="RIGHT")changeDirection("LEFT");
    }
	
	public void changeDirection(String direction){
		//end case: if ! UP/DOWN/LEFT/RIGHT
		Thread t = new Thread();
			if(!direction.equals("UP")&&!direction.equals("DOWN")&&!direction.equals("LEFT")&&!direction.equals("RIGHT"))return;
			for(int i=0; i<linkNum; i++){
				snake.get(i).setHeaded(direction);
				try {
					t.sleep(90);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				move();
			}	
	}
	
	public void move(){

		//goes through all the links and apply the move that is set in them
				for(int i=0; i<linkNum; i++){
					
					if(snake.get(i).getHeaded().equals("RIGHT")){
						snake.get(i).setDx(snake.get(i).getDx()+distance);	
					}else
						if(snake.get(i).getHeaded().equals("LEFT")){
							snake.get(i).setDx(snake.get(i).getDx()-distance);
						}else
							if(snake.get(i).getHeaded().equals("UP")){
								snake.get(i).setDy(snake.get(i).getDy()+distance);
							}else
								if(snake.get(i).getHeaded().equals("DOWN")){
									snake.get(i).setDy(snake.get(i).getDy()-distance);
								}
				}
	}
	//-------------------

	public ArrayList<SnakeLink> getSnake() {
		return snake;
	}

	public void setSnake(ArrayList<SnakeLink> snake) {
		this.snake = snake;
	}

	public double getPxSize() {
		return pxSize;
	}

	public void setPxSize(double pxSize) {
		this.pxSize = pxSize;
	}

	public double getDistance() {
		return distance;
	}

	public void setDistance(double distance) {
		this.distance = distance;
	}

	public static int getLinkNum() {
		return linkNum;
	}

	public static void setLinkNum(int linkNum) {
		Snake.linkNum = linkNum;
	}
	
	
}

SnakeLink (each link of the snake)

package Snake;

public class SnakeLink {
	private double dx;
	private double dy;
	private String headed;
	private static int linkNum=0;
	
	public SnakeLink(){	
		headed="RIGHT";
		linkNum++;
	}
	
	public SnakeLink(double dX, double dy){
		this.dx = dx;
		this.dy = dy;
		headed="RIGHT";
		linkNum++;
	}
	
	public double getDx() {
		return dx;
	}
	public void setDx(double dx) {
		this.dx = dx;
	}
	public double getDy() {
		return dy;
	}
	public void setDy(double dy) {
		this.dy = dy;
	}
	public String getHeaded() {
		return headed;
	}
	public void setHeaded(String headed) {
		this.headed = headed;
	}
	public int getLinkNum() {
		return linkNum;
	}
	public void setLinkNum(int linkNum) {
		this.linkNum = linkNum;
	}
	
}

Apple class

package Snake;

import java.util.Random;

public class Apple {
	private double xPos;
	private double yPos;
	private double pxSize;
	
	public Apple(double worldSize,double pixelSize){
		placeApple(worldSize,pixelSize);
	}
	
	public void drawApple(boolean toDraw){
		if(toDraw)
		StdDraw.filledSquare(xPos, yPos, pxSize);
	}

	public double getxPos() {
		return xPos;
	}

	public void setxPos(double xPos) {
		this.xPos = xPos;
	}

	public double getyPos() {
		return yPos;
	}

	public void setyPos(double yPos) {
		this.yPos = yPos;
	}
	
	public void placeApple(double worldSize,double pixelSize){
		Random rand = new Random();
		int lengthOfWorld = (int)(worldSize/pixelSize);
		xPos = rand.nextInt(lengthOfWorld+1)*pixelSize;
		yPos = rand.nextInt(lengthOfWorld+1)*pixelSize;
		pxSize = pixelSize;
		
	}
	
	
	
}

[Norm]

Where is the StdDraw class defined? Why not use standard java classes?

[Yakg]

Where is the StdDraw class defined? Why not use standard java classes?

I forgot to attach it, here it is:

package SnakeMovement;
/*************************************************************************
 *  Compilation:  javac StdDraw.java
 *  Execution:    java StdDraw
 *
 *  Standard drawing library. This class provides a basic capability for
 *  creating drawings with your programs. It uses a simple graphics model that
 *  allows you to create drawings consisting of points, lines, and curves
 *  in a window on your computer and to save the drawings to a file.
 *
 *  Todo
 *  ----
 *    -  Add support for gradient fill, etc.
 *
 *  Remarks
 *  -------
 *    -  don't use AffineTransform for rescaling since it inverts
 *       images and strings
 *    -  careful using setFont in inner loop within an animation -
 *       it can cause flicker
 *
 *************************************************************************/

import java.applet.AudioClip;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import java.util.LinkedList;
import java.util.TreeSet;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.util.HashMap;

/**
 *  <i>Standard draw</i>. This class provides a basic capability for
 *  creating drawings with your programs. It uses a simple graphics model that
 *  allows you to create drawings consisting of points, lines, and curves
 *  in a window on your computer and to save the drawings to a file.
 *  <p>
 *  For additional documentation, see <a href="http://introcs.cs.princeton.edu/15inout">Section 1.5</a> of
 *  <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  This version adds caching of loaded Image objects (add by Keith Vertanen).
 *
 */
public final class StdDraw implements ActionListener, MouseListener, MouseMotionListener, KeyListener {

    // pre-defined colors
    public static final Color BLACK      = Color.BLACK;
    public static final Color BLUE       = Color.BLUE;
    public static final Color CYAN       = Color.CYAN;
    public static final Color DARK_GRAY  = Color.DARK_GRAY;
    public static final Color GRAY       = Color.GRAY;
    public static final Color GREEN      = Color.GREEN;
    public static final Color LIGHT_GRAY = Color.LIGHT_GRAY;
    public static final Color MAGENTA    = Color.MAGENTA;
    public static final Color ORANGE     = Color.ORANGE;
    public static final Color PINK       = Color.PINK;
    public static final Color RED        = Color.RED;
    public static final Color WHITE      = Color.WHITE;
    public static final Color YELLOW     = Color.YELLOW;

    /**
     * Shade of blue used in Introduction to Programming in Java.
     * It is Pantone 300U. The RGB values are approximately (9, 90, 266).
     */
    public static final Color BOOK_BLUE       = new Color(  9,  90, 166);
    public static final Color BOOK_LIGHT_BLUE = new Color(103, 198, 243);

    /**
     * Shade of red used in Algorithms 4th edition.
     * It is Pantone 1805U. The RGB values are approximately (150, 35, 31).
     */
    public static final Color BOOK_RED = new Color(150, 35, 31);

    // default colors
    private static final Color DEFAULT_PEN_COLOR   = BLACK;
    private static final Color DEFAULT_CLEAR_COLOR = WHITE;

    // current pen color
    private static Color penColor;

    // default canvas size is DEFAULT_SIZE-by-DEFAULT_SIZE
    private static final int DEFAULT_SIZE = 512;
    private static int width  = DEFAULT_SIZE;
    private static int height = DEFAULT_SIZE;

    // default pen radius
    private static final double DEFAULT_PEN_RADIUS = 0.002;

    // current pen radius
    private static double penRadius;

    // show we draw immediately or wait until next show?
    private static boolean defer = false;

    // boundary of drawing canvas, 5% border
    private static final double BORDER = 0.05;
    private static final double DEFAULT_XMIN = 0.0;
    private static final double DEFAULT_XMAX = 1.0;
    private static final double DEFAULT_YMIN = 0.0;
    private static final double DEFAULT_YMAX = 1.0;
    private static double xmin, ymin, xmax, ymax;

    // for synchronization
    private static Object mouseLock = new Object();
    private static Object keyLock = new Object();

    // default font
    private static final Font DEFAULT_FONT = new Font("SansSerif", Font.PLAIN, 16);

    // current font
    private static Font font;

    // double buffered graphics
    private static BufferedImage offscreenImage, onscreenImage;
    private static Graphics2D offscreen, onscreen;

    // singleton for callbacks: avoids generation of extra .class files
    private static StdDraw std = new StdDraw();

    // the frame for drawing to the screen
    private static JFrame frame;

    // mouse state
    private static boolean mousePressed = false;
    private static double mouseX = 0;
    private static double mouseY = 0;

    // queue of typed key characters
    private static LinkedList<Character> keysTyped = new LinkedList<Character>();

    // set of key codes currently pressed down
    private static TreeSet<Integer> keysDown = new TreeSet<Integer>();
    
    // For caching of Image files, prevents glitches in video games, etc.
    private static HashMap<String, Image> imageCache = new HashMap<String, Image>();
    private static boolean imageCaching = true;
    
    // Turn image caching on or off, by default caching is on.
    // This helps prevents glitches if images are drawn frequently.
    public static void setCaching(boolean caching)
    {
        imageCaching = caching;
        if (!imageCaching)
            imageCache.clear();
    }
    
    // not instantiable
    private StdDraw() { }


    // static initializer
    static { init(); }

    /**
     * Set the window size to the default size 512-by-512 pixels.
     */
    public static void setCanvasSize() {
        setCanvasSize(DEFAULT_SIZE, DEFAULT_SIZE);
    }

    /**
     * Set the window size to w-by-h pixels.
     *
     * @param w the width as a number of pixels
     * @param h the height as a number of pixels
     * @throws a RunTimeException if the width or height is 0 or negative
     */
    public static void setCanvasSize(int w, int h) {
        if (w < 1 || h < 1) throw new RuntimeException("width and height must be positive");
        width = w;
        height = h;
        init();
    }

    // init
    private static void init() {
        if (frame != null) frame.setVisible(false);
        frame = new JFrame();
        offscreenImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        onscreenImage  = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        offscreen = offscreenImage.createGraphics();
        onscreen  = onscreenImage.createGraphics();
        setXscale();
        setYscale();
        offscreen.setColor(DEFAULT_CLEAR_COLOR);
        offscreen.fillRect(0, 0, width, height);
        setPenColor();
        setPenRadius();
        setFont();
        clear();

        // add antialiasing
        RenderingHints hints = new RenderingHints(RenderingHints.KEY_ANTIALIASING,
                                                  RenderingHints.VALUE_ANTIALIAS_ON);
        hints.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        offscreen.addRenderingHints(hints);

        // frame stuff
        ImageIcon icon = new ImageIcon(onscreenImage);
        JLabel draw = new JLabel(icon);

        draw.addMouseListener(std);
        draw.addMouseMotionListener(std);

        frame.setContentPane(draw);
        frame.addKeyListener(std);    // JLabel cannot get keyboard focus
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);            // closes all windows
        // frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);      // closes only current window
        frame.setTitle("Standard Draw");
        frame.setJMenuBar(createMenuBar());
        frame.pack();
        frame.requestFocusInWindow();
        frame.setVisible(true);
    }

    // create the menu bar (changed to private)
    private static JMenuBar createMenuBar() {
        JMenuBar menuBar = new JMenuBar();
        JMenu menu = new JMenu("File");
        menuBar.add(menu);
        JMenuItem menuItem1 = new JMenuItem(" Save...   ");
        menuItem1.addActionListener(std);
        menuItem1.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_S,
                                Toolkit.getDefaultToolkit().getMenuShortcutKeyMask()));
        menu.add(menuItem1);
        return menuBar;
    }


   /*************************************************************************
    *  User and screen coordinate systems
    *************************************************************************/

    /**
     * Set the x-scale to be the default (between 0.0 and 1.0).
     */
    public static void setXscale() { setXscale(DEFAULT_XMIN, DEFAULT_XMAX); }

    /**
     * Set the y-scale to be the default (between 0.0 and 1.0).
     */
    public static void setYscale() { setYscale(DEFAULT_YMIN, DEFAULT_YMAX); }

    /**
     * Set the x-scale (a 10% border is added to the values)
     * @param min the minimum value of the x-scale
     * @param max the maximum value of the x-scale
     */
    public static void setXscale(double min, double max) {
        double size = max - min;
        xmin = min - BORDER * size;
        xmax = max + BORDER * size;
    }

    /**
     * Set the y-scale (a 10% border is added to the values).
     * @param min the minimum value of the y-scale
     * @param max the maximum value of the y-scale
     */
    public static void setYscale(double min, double max) {
        double size = max - min;
        ymin = min - BORDER * size;
        ymax = max + BORDER * size;
    }

    /**
     * Set the x-scale and y-scale (a 10% border is added to the values)
     * @param min the minimum value of the x- and y-scales
     * @param max the maximum value of the x- and y-scales
     */
    public static void setScale(double min, double max) {
        setXscale(min, max);
        setYscale(min, max);
    }

    // helper functions that scale from user coordinates to screen coordinates and back
    private static double  scaleX(double x) { return width  * (x - xmin) / (xmax - xmin); }
    private static double  scaleY(double y) { return height * (ymax - y) / (ymax - ymin); }
    private static double factorX(double w) { return w * width  / Math.abs(xmax - xmin);  }
    private static double factorY(double h) { return h * height / Math.abs(ymax - ymin);  }
    private static double   userX(double x) { return xmin + x * (xmax - xmin) / width;    }
    private static double   userY(double y) { return ymax - y * (ymax - ymin) / height;   }


    /**
     * Clear the screen to the default color (white).
     */
    public static void clear() { clear(DEFAULT_CLEAR_COLOR); }
    /**
     * Clear the screen to the given color.
     * @param color the Color to make the background
     */
    public static void clear(Color color) {
        offscreen.setColor(color);
        offscreen.fillRect(0, 0, width, height);
        offscreen.setColor(penColor);
        draw();
    }

    /**
     * Get the current pen radius.
     */
    public static double getPenRadius() { return penRadius; }

    /**
     * Set the pen size to the default (.002).
     */
    public static void setPenRadius() { setPenRadius(DEFAULT_PEN_RADIUS); }
    /**
     * Set the radius of the pen to the given size.
     * @param r the radius of the pen
     * @throws RuntimeException if r is negative
     */
    public static void setPenRadius(double r) {
        if (r < 0) throw new RuntimeException("pen radius must be positive");
        penRadius = r * DEFAULT_SIZE;
        BasicStroke stroke = new BasicStroke((float) penRadius, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
        // BasicStroke stroke = new BasicStroke((float) penRadius);
        offscreen.setStroke(stroke);
    }

    /**
     * Get the current pen color.
     */
    public static Color getPenColor() { return penColor; }

    /**
     * Set the pen color to the default color (black).
     */
    public static void setPenColor() { setPenColor(DEFAULT_PEN_COLOR); }
    /**
     * Set the pen color to the given color. The available pen colors are
     * BLACK, BLUE, CYAN, DARK_GRAY, GRAY, GREEN, LIGHT_GRAY, MAGENTA,
     * ORANGE, PINK, RED, WHITE, and YELLOW.
     * @param color the Color to make the pen
     */
    public static void setPenColor(Color color) {
        penColor = color;
        offscreen.setColor(penColor);
    }

    /**
     * Get the current font.
     */
    public static Font getFont() { return font; }

    /**
     * Set the font to the default font (sans serif, 16 point).
     */
    public static void setFont() { setFont(DEFAULT_FONT); }

    /**
     * Set the font to the given value.
     * @param f the font to make text
     */
    public static void setFont(Font f) { font = f; }


   /*************************************************************************
    *  Drawing geometric shapes.
    *************************************************************************/

    /**
     * Draw a line from (x0, y0) to (x1, y1).
     * @param x0 the x-coordinate of the starting point
     * @param y0 the y-coordinate of the starting point
     * @param x1 the x-coordinate of the destination point
     * @param y1 the y-coordinate of the destination point
     */
    public static void line(double x0, double y0, double x1, double y1) {
        offscreen.draw(new Line2D.Double(scaleX(x0), scaleY(y0), scaleX(x1), scaleY(y1)));
        draw();
    }

    /**
     * Draw one pixel at (x, y).
     * @param x the x-coordinate of the pixel
     * @param y the y-coordinate of the pixel
     */
    private static void pixel(double x, double y) {
        offscreen.fillRect((int) Math.round(scaleX(x)), (int) Math.round(scaleY(y)), 1, 1);
    }

    /**
     * Draw a point at (x, y).
     * @param x the x-coordinate of the point
     * @param y the y-coordinate of the point
     */
    public static void point(double x, double y) {
        double xs = scaleX(x);
        double ys = scaleY(y);
        double r = penRadius;
        // double ws = factorX(2*r);
        // double hs = factorY(2*r);
        // if (ws <= 1 && hs <= 1) pixel(x, y);
        if (r <= 1) pixel(x, y);
        else offscreen.fill(new Ellipse2D.Double(xs - r/2, ys - r/2, r, r));
        draw();
    }

    /**
     * Draw a circle of radius r, centered on (x, y).
     * @param x the x-coordinate of the center of the circle
     * @param y the y-coordinate of the center of the circle
     * @param r the radius of the circle
     * @throws RuntimeException if the radius of the circle is negative
     */
    public static void circle(double x, double y, double r) {
        if (r < 0) throw new RuntimeException("circle radius can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*r);
        double hs = factorY(2*r);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.draw(new Ellipse2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }

    /**
     * Draw filled circle of radius r, centered on (x, y).
     * @param x the x-coordinate of the center of the circle
     * @param y the y-coordinate of the center of the circle
     * @param r the radius of the circle
     * @throws RuntimeException if the radius of the circle is negative
     */
    public static void filledCircle(double x, double y, double r) {
        if (r < 0) throw new RuntimeException("circle radius can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*r);
        double hs = factorY(2*r);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.fill(new Ellipse2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }


    /**
     * Draw an ellipse with given semimajor and semiminor axes, centered on (x, y).
     * @param x the x-coordinate of the center of the ellipse
     * @param y the y-coordinate of the center of the ellipse
     * @param semiMajorAxis is the semimajor axis of the ellipse
     * @param semiMinorAxis is the semiminor axis of the ellipse
     * @throws RuntimeException if either of the axes are negative
     */
    public static void ellipse(double x, double y, double semiMajorAxis, double semiMinorAxis) {
        if (semiMajorAxis < 0) throw new RuntimeException("ellipse semimajor axis can't be negative");
        if (semiMinorAxis < 0) throw new RuntimeException("ellipse semiminor axis can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*semiMajorAxis);
        double hs = factorY(2*semiMinorAxis);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.draw(new Ellipse2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }

    /**
     * Draw an ellipse with given semimajor and semiminor axes, centered on (x, y).
     * @param x the x-coordinate of the center of the ellipse
     * @param y the y-coordinate of the center of the ellipse
     * @param semiMajorAxis is the semimajor axis of the ellipse
     * @param semiMinorAxis is the semiminor axis of the ellipse
     * @throws RuntimeException if either of the axes are negative
     */
    public static void filledEllipse(double x, double y, double semiMajorAxis, double semiMinorAxis) {
        if (semiMajorAxis < 0) throw new RuntimeException("ellipse semimajor axis can't be negative");
        if (semiMinorAxis < 0) throw new RuntimeException("ellipse semiminor axis can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*semiMajorAxis);
        double hs = factorY(2*semiMinorAxis);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.fill(new Ellipse2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }


    /**
     * Draw an arc of radius r, centered on (x, y), from angle1 to angle2 (in degrees).
     * @param x the x-coordinate of the center of the circle
     * @param y the y-coordinate of the center of the circle
     * @param r the radius of the circle
     * @param angle1 the starting angle. 0 would mean an arc beginning at 3 o'clock.
     * @param angle2 the angle at the end of the arc. For example, if
     *        you want a 90 degree arc, then angle2 should be angle1 + 90.
     * @throws RuntimeException if the radius of the circle is negative
     */
    public static void arc(double x, double y, double r, double angle1, double angle2) {
        if (r < 0) throw new RuntimeException("arc radius can't be negative");
        while (angle2 < angle1) angle2 += 360;
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*r);
        double hs = factorY(2*r);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.draw(new Arc2D.Double(xs - ws/2, ys - hs/2, ws, hs, angle1, angle2 - angle1, Arc2D.OPEN));
        draw();
    }

    /**
     * Draw a square of side length 2r, centered on (x, y).
     * @param x the x-coordinate of the center of the square
     * @param y the y-coordinate of the center of the square
     * @param r radius is half the length of any side of the square
     * @throws RuntimeException if r is negative
     */
    public static void square(double x, double y, double r) {
        if (r < 0) throw new RuntimeException("square side length can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*r);
        double hs = factorY(2*r);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.draw(new Rectangle2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }

    /**
     * Draw a filled square of side length 2r, centered on (x, y).
     * @param x the x-coordinate of the center of the square
     * @param y the y-coordinate of the center of the square
     * @param r radius is half the length of any side of the square
     * @throws RuntimeException if r is negative
     */
    public static void filledSquare(double x, double y, double r) {
        if (r < 0) throw new RuntimeException("square side length can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*r);
        double hs = factorY(2*r);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.fill(new Rectangle2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }


    /**
     * Draw a rectangle of given half width and half height, centered on (x, y).
     * @param x the x-coordinate of the center of the rectangle
     * @param y the y-coordinate of the center of the rectangle
     * @param halfWidth is half the width of the rectangle
     * @param halfHeight is half the height of the rectangle
     * @throws RuntimeException if halfWidth or halfHeight is negative
     */
    public static void rectangle(double x, double y, double halfWidth, double halfHeight) {
        if (halfWidth  < 0) throw new RuntimeException("half width can't be negative");
        if (halfHeight < 0) throw new RuntimeException("half height can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*halfWidth);
        double hs = factorY(2*halfHeight);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.draw(new Rectangle2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }

    /**
     * Draw a filled rectangle of given half width and half height, centered on (x, y).
     * @param x the x-coordinate of the center of the rectangle
     * @param y the y-coordinate of the center of the rectangle
     * @param halfWidth is half the width of the rectangle
     * @param halfHeight is half the height of the rectangle
     * @throws RuntimeException if halfWidth or halfHeight is negative
     */
    public static void filledRectangle(double x, double y, double halfWidth, double halfHeight) {
        if (halfWidth  < 0) throw new RuntimeException("half width can't be negative");
        if (halfHeight < 0) throw new RuntimeException("half height can't be negative");
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(2*halfWidth);
        double hs = factorY(2*halfHeight);
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else offscreen.fill(new Rectangle2D.Double(xs - ws/2, ys - hs/2, ws, hs));
        draw();
    }


    /**
     * Draw a polygon with the given (x[i], y[i]) coordinates.
     * @param x an array of all the x-coordindates of the polygon
     * @param y an array of all the y-coordindates of the polygon
     */
    public static void polygon(double[] x, double[] y) {
        int N = x.length;
        GeneralPath path = new GeneralPath();
        path.moveTo((float) scaleX(x[0]), (float) scaleY(y[0]));
        for (int i = 0; i < N; i++)
            path.lineTo((float) scaleX(x[i]), (float) scaleY(y[i]));
        path.closePath();
        offscreen.draw(path);
        draw();
    }

    /**
     * Draw a filled polygon with the given (x[i], y[i]) coordinates.
     * @param x an array of all the x-coordindates of the polygon
     * @param y an array of all the y-coordindates of the polygon
     */
    public static void filledPolygon(double[] x, double[] y) {
        int N = x.length;
        GeneralPath path = new GeneralPath();
        path.moveTo((float) scaleX(x[0]), (float) scaleY(y[0]));
        for (int i = 0; i < N; i++)
            path.lineTo((float) scaleX(x[i]), (float) scaleY(y[i]));
        path.closePath();
        offscreen.fill(path);
        draw();
    }



   /*************************************************************************
    *  Drawing images.
    *************************************************************************/

    // get an image from the given filename
    private static Image getImage(String filename) {

        Image result = null;
        if (imageCaching)
            result = imageCache.get(filename);
        
        if (result == null)
        {
            // to read from file
            ImageIcon icon = new ImageIcon(filename);
    
            // try to read from URL
            if ((icon == null) || (icon.getImageLoadStatus() != MediaTracker.COMPLETE)) {
                try {
                    URL url = new URL(filename);
                    icon = new ImageIcon(url);
                } catch (Exception e) { /* not a url */ }
            }
    
            // in case file is inside a .jar
            if ((icon == null) || (icon.getImageLoadStatus() != MediaTracker.COMPLETE)) {
                URL url = StdDraw.class.getResource(filename);
                if (url == null) throw new RuntimeException("image " + filename + " not found");
                icon = new ImageIcon(url);
            }
            result = icon.getImage();
            if (imageCaching)
                imageCache.put(filename, result);
        }
        
        return result;
    }

    /**
     * Draw picture (gif, jpg, or png) centered on (x, y).
     * @param x the center x-coordinate of the image
     * @param y the center y-coordinate of the image
     * @param s the name of the image/picture, e.g., "ball.gif"
     * @throws RuntimeException if the image is corrupt
     */
    public static void picture(double x, double y, String s) {
        Image image = getImage(s);
        double xs = scaleX(x);
        double ys = scaleY(y);
        int ws = image.getWidth(null);
        int hs = image.getHeight(null);
        if (ws < 0 || hs < 0) throw new RuntimeException("image " + s + " is corrupt");

        offscreen.drawImage(image, (int) Math.round(xs - ws/2.0), (int) Math.round(ys - hs/2.0), null);
        draw();
    }

    /**
     * Draw picture (gif, jpg, or png) centered on (x, y),
     * rotated given number of degrees
     * @param x the center x-coordinate of the image
     * @param y the center y-coordinate of the image
     * @param s the name of the image/picture, e.g., "ball.gif"
     * @param degrees is the number of degrees to rotate counterclockwise
     * @throws RuntimeException if the image is corrupt
     */
    public static void picture(double x, double y, String s, double degrees) {
        Image image = getImage(s);
        double xs = scaleX(x);
        double ys = scaleY(y);
        int ws = image.getWidth(null);
        int hs = image.getHeight(null);
        if (ws < 0 || hs < 0) throw new RuntimeException("image " + s + " is corrupt");

        offscreen.rotate(Math.toRadians(-degrees), xs, ys);
        offscreen.drawImage(image, (int) Math.round(xs - ws/2.0), (int) Math.round(ys - hs/2.0), null);
        offscreen.rotate(Math.toRadians(+degrees), xs, ys);

        draw();
    }

    /**
     * Draw picture (gif, jpg, or png) centered on (x, y), rescaled to w-by-h.
     * @param x the center x coordinate of the image
     * @param y the center y coordinate of the image
     * @param s the name of the image/picture, e.g., "ball.gif"
     * @param w the width of the image
     * @param h the height of the image
     * @throws RuntimeException if the width height are negative
     * @throws RuntimeException if the image is corrupt
     */
    public static void picture(double x, double y, String s, double w, double h) {
        Image image = getImage(s);
        double xs = scaleX(x);
        double ys = scaleY(y);
        if (w < 0) throw new RuntimeException("width is negative: " + w);
        if (h < 0) throw new RuntimeException("height is negative: " + h);
        double ws = factorX(w);
        double hs = factorY(h);
        if (ws < 0 || hs < 0) throw new RuntimeException("image " + s + " is corrupt");
        if (ws <= 1 && hs <= 1) pixel(x, y);
        else {
            offscreen.drawImage(image, (int) Math.round(xs - ws/2.0),
                                       (int) Math.round(ys - hs/2.0),
                                       (int) Math.round(ws),
                                       (int) Math.round(hs), null);
        }
        draw();
    }


    /**
     * Draw picture (gif, jpg, or png) centered on (x, y), rotated
     * given number of degrees, rescaled to w-by-h.
     * @param x the center x-coordinate of the image
     * @param y the center y-coordinate of the image
     * @param s the name of the image/picture, e.g., "ball.gif"
     * @param w the width of the image
     * @param h the height of the image
     * @param degrees is the number of degrees to rotate counterclockwise
     * @throws RuntimeException if the image is corrupt
     */
    public static void picture(double x, double y, String s, double w, double h, double degrees) {
        Image image = getImage(s);
        double xs = scaleX(x);
        double ys = scaleY(y);
        double ws = factorX(w);
        double hs = factorY(h);
        if (ws < 0 || hs < 0) throw new RuntimeException("image " + s + " is corrupt");
        if (ws <= 1 && hs <= 1) pixel(x, y);

        offscreen.rotate(Math.toRadians(-degrees), xs, ys);
        offscreen.drawImage(image, (int) Math.round(xs - ws/2.0),
                                   (int) Math.round(ys - hs/2.0),
                                   (int) Math.round(ws),
                                   (int) Math.round(hs), null);
        offscreen.rotate(Math.toRadians(+degrees), xs, ys);

        draw();
    }


   /*************************************************************************
    *  Drawing text.
    *************************************************************************/

    /**
     * Write the given text string in the current font, centered on (x, y).
     * @param x the center x-coordinate of the text
     * @param y the center y-coordinate of the text
     * @param s the text
     */
    public static void text(double x, double y, String s) {
        offscreen.setFont(font);
        FontMetrics metrics = offscreen.getFontMetrics();
        double xs = scaleX(x);
        double ys = scaleY(y);
        int ws = metrics.stringWidth(s);
        int hs = metrics.getDescent();
        offscreen.drawString(s, (float) (xs - ws/2.0), (float) (ys + hs));
        draw();
    }

    /**
     * Write the given text string in the current font, centered on (x, y) and
     * rotated by the specified number of degrees  
     * @param x the center x-coordinate of the text
     * @param y the center y-coordinate of the text
     * @param s the text
     * @param degrees is the number of degrees to rotate counterclockwise
     */
    public static void text(double x, double y, String s, double degrees) {
        double xs = scaleX(x);
        double ys = scaleY(y);
        offscreen.rotate(Math.toRadians(-degrees), xs, ys);
        text(x, y, s);
        offscreen.rotate(Math.toRadians(+degrees), xs, ys);
    }


    /**
     * Write the given text string in the current font, left-aligned at (x, y).
     * @param x the x-coordinate of the text
     * @param y the y-coordinate of the text
     * @param s the text
     */
    public static void textLeft(double x, double y, String s) {
        offscreen.setFont(font);
        FontMetrics metrics = offscreen.getFontMetrics();
        double xs = scaleX(x);
        double ys = scaleY(y);
        int hs = metrics.getDescent();
        offscreen.drawString(s, (float) (xs), (float) (ys + hs));
        show();
    }

    /**
     * Write the given text string in the current font, right-aligned at (x, y).
     * @param x the x-coordinate of the text
     * @param y the y-coordinate of the text
     * @param s the text
     */
    public static void textRight(double x, double y, String s) {
        offscreen.setFont(font);
        FontMetrics metrics = offscreen.getFontMetrics();
        double xs = scaleX(x);
        double ys = scaleY(y);
        int ws = metrics.stringWidth(s);
        int hs = metrics.getDescent();
        offscreen.drawString(s, (float) (xs - ws), (float) (ys + hs));
        show();
    }



    /**
     * Display on screen, pause for t milliseconds, and turn on
     * <em>animation mode</em>: subsequent calls to
     * drawing methods such as <tt>line()</tt>, <tt>circle()</tt>, and <tt>square()</tt>
     * will not be displayed on screen until the next call to <tt>show()</tt>.
     * This is useful for producing animations (clear the screen, draw a bunch of shapes,
     * display on screen for a fixed amount of time, and repeat). It also speeds up
     * drawing a huge number of shapes (call <tt>show(0)</tt> to defer drawing
     * on screen, draw the shapes, and call <tt>show(0)</tt> to display them all
     * on screen at once).
     * @param t number of milliseconds
     */
    public static void show(int t) {
        defer = false;
        draw();
        try { Thread.currentThread().sleep(t); }
        catch (InterruptedException e) { System.out.println("Error sleeping"); }
        defer = true;
    }


    /**
     * Display on-screen and turn off animation mode:
     * subsequent calls to
     * drawing methods such as <tt>line()</tt>, <tt>circle()</tt>, and <tt>square()</tt>
     * will be displayed on screen when called. This is the default.
     */
    public static void show() {
        defer = false;
        draw();
    }

    // draw onscreen if defer is false
    private static void draw() {
        if (defer) return;
        onscreen.drawImage(offscreenImage, 0, 0, null);
        frame.repaint();
    }


   /*************************************************************************
    *  Save drawing to a file.
    *************************************************************************/

    /**
     * Save to file - suffix must be png, jpg, or gif.
     * @param filename the name of the file with one of the required suffixes
     */
    public static void save(String filename) {
        File file = new File(filename);
        String suffix = filename.substring(filename.lastIndexOf('.') + 1);

        // png files
        if (suffix.toLowerCase().equals("png")) {
            try { ImageIO.write(offscreenImage, suffix, file); }
            catch (IOException e) { e.printStackTrace(); }
        }

        // need to change from ARGB to RGB for jpeg
        // reference: http://archives.java.sun.com/cgi-bin/wa?A2=ind0404&L=java2d-interest&D=0&P=2727
        else if (suffix.toLowerCase().equals("jpg")) {
            WritableRaster raster = offscreenImage.getRaster();
            WritableRaster newRaster;
            newRaster = raster.createWritableChild(0, 0, width, height, 0, 0, new int[] {0, 1, 2});
            DirectColorModel cm = (DirectColorModel) offscreenImage.getColorModel();
            DirectColorModel newCM = new DirectColorModel(cm.getPixelSize(),
                                                          cm.getRedMask(),
                                                          cm.getGreenMask(),
                                                          cm.getBlueMask());
            BufferedImage rgbBuffer = new BufferedImage(newCM, newRaster, false,  null);
            try { ImageIO.write(rgbBuffer, suffix, file); }
            catch (IOException e) { e.printStackTrace(); }
        }

        else {
            System.out.println("Invalid image file type: " + suffix);
        }
    }


    /**
     * This method cannot be called directly.
     */
    public void actionPerformed(ActionEvent e) {
        FileDialog chooser = new FileDialog(StdDraw.frame, "Use a .png or .jpg extension", FileDialog.SAVE);
        chooser.setVisible(true);
        String filename = chooser.getFile();
        if (filename != null) {
            StdDraw.save(chooser.getDirectory() + File.separator + chooser.getFile());
        }
    }


   /*************************************************************************
    *  Mouse interactions.
    *************************************************************************/

    /**
     * Is the mouse being pressed?
     * @return true or false
     */
    public static boolean mousePressed() {
        synchronized (mouseLock) {
            return mousePressed;
        }
    }

    /**
     * What is the x-coordinate of the mouse?
     * @return the value of the x-coordinate of the mouse
     */
    public static double mouseX() {
        synchronized (mouseLock) {
            return mouseX;
        }
    }

    /**
     * What is the y-coordinate of the mouse?
     * @return the value of the y-coordinate of the mouse
     */
    public static double mouseY() {
        synchronized (mouseLock) {
            return mouseY;
        }
    }


    /**
     * This method cannot be called directly.
     */
    public void mouseClicked(MouseEvent e) { }

    /**
     * This method cannot be called directly.
     */
    public void mouseEntered(MouseEvent e) { }

    /**
     * This method cannot be called directly.
     */
    public void mouseExited(MouseEvent e) { }

    /**
     * This method cannot be called directly.
     */
    public void mousePressed(MouseEvent e) {
        synchronized (mouseLock) {
            mouseX = StdDraw.userX(e.getX());
            mouseY = StdDraw.userY(e.getY());
            mousePressed = true;
        }
    }

    /**
     * This method cannot be called directly.
     */
    public void mouseReleased(MouseEvent e) {
        synchronized (mouseLock) {
            mousePressed = false;
        }
    }

    /**
     * This method cannot be called directly.
     */
    public void mouseDragged(MouseEvent e)  {
        synchronized (mouseLock) {
            mouseX = StdDraw.userX(e.getX());
            mouseY = StdDraw.userY(e.getY());
        }
    }

    /**
     * This method cannot be called directly.
     */
    public void mouseMoved(MouseEvent e) {
        synchronized (mouseLock) {
            mouseX = StdDraw.userX(e.getX());
            mouseY = StdDraw.userY(e.getY());
        }
    }


   /*************************************************************************
    *  Keyboard interactions.
    *************************************************************************/

    /**
     * Has the user typed a key?
     * @return true if the user has typed a key, false otherwise
     */
    public static boolean hasNextKeyTyped() {
        synchronized (keyLock) {
            return !keysTyped.isEmpty();
        }
    }

    /**
     * What is the next key that was typed by the user? This method returns
     * a Unicode character corresponding to the key typed (such as 'a' or 'A').
     * It cannot identify action keys (such as F1
     * and arrow keys) or modifier keys (such as control).
     * @return the next Unicode key typed
     */
    public static char nextKeyTyped() {
        synchronized (keyLock) {
            return keysTyped.removeLast();
        }
    }

    /**
     * Is the keycode currently being pressed? This method takes as an argument
     * the keycode (corresponding to a physical key). It can handle action keys
     * (such as F1 and arrow keys) and modifier keys (such as shift and control).
     * See <a href = "http://download.oracle.com/javase/6/docs/api/java/awt/event/KeyEvent.html">KeyEvent.java</a>
     * for a description of key codes.
     * @return true if keycode is currently being pressed, false otherwise
     */
    public static boolean isKeyPressed(int keycode) {
        return keysDown.contains(keycode);
    }


    /**
     * This method cannot be called directly.
     */
    public void keyTyped(KeyEvent e) {
        synchronized (keyLock) {
            keysTyped.addFirst(e.getKeyChar());
        }
    }

    /**
     * This method cannot be called directly.
     */
    public void keyPressed(KeyEvent e) {
        keysDown.add(e.getKeyCode());
    }

    /**
     * This method cannot be called directly.
     */
    public void keyReleased(KeyEvent e) {
        keysDown.remove(e.getKeyCode());
    }




    /**
     * Test client.
     */
    public static void main(String[] args) {
        StdDraw.square(.2, .8, .1);
        StdDraw.filledSquare(.8, .8, .2);
        StdDraw.circle(.8, .2, .2);

        StdDraw.setPenColor(StdDraw.BOOK_RED);
        StdDraw.setPenRadius(.02);
        StdDraw.arc(.8, .2, .1, 200, 45);

        // draw a blue diamond
        StdDraw.setPenRadius();
        StdDraw.setPenColor(StdDraw.BOOK_BLUE);
        double[] x = { .1, .2, .3, .2 };
        double[] y = { .2, .3, .2, .1 };
        StdDraw.filledPolygon(x, y);

        // text
        StdDraw.setPenColor(StdDraw.BLACK);
        StdDraw.text(0.2, 0.5, "black text");
        StdDraw.setPenColor(StdDraw.WHITE);
        StdDraw.text(0.8, 0.8, "white text");
    }

}

I guess it would be better getting used to a more traditional way, StdDraw I think helps but only a little, there's not a huge difference..

[Norm]

Sorry, That is too much code for me.

Try replacing your usage of that class with native java se classes. There could be more people willing to help.

The StdDraw class is controlling what is displayed. You probably need an expert with that class to help you.

[pbrockway2]

I don't think calling sleep() in your changeDirection() method is the way to go.

If you are using the StdDraw library - and if this is course work or something that would be a reason for doing so - then the first place to go is the link given in its source code: 1.5 Input and Output.

(a) Read that page, especially the section "Standard Drawing" >> "Computer animations"
(b) Take the example code given there (the bouncing ball), compile and run it. Read that code line by line by line making sure you understand each call to the StdDraw code. Let nothing slip by as "magic".
(c) Step back from your existing code and implement a very simple snake that does nothing more than move convincingly, keeping within the wall.
(c2 ... c_n) Add other things like keyboard control until you have the snake/apple thing according to what you want (or to the specifications you were given)

Using a third party library inevitably involves doing things the way the library dictates. (a)->(c) above describe the steps I use when first faced with some library that is new to me.

The important thing is to work one small step at a time as that gives you precise questions to ask here: "what does <expression> in the docs mean?", "why does the following code give <compiler error> and what might I do about it?", "when I use the following code to start/stop the bouncing ball <bad thing> happens - why does that happen and what might I try instead?".

At the moment you have thrown in a sleep() call and are stumped! Don't worry, everyone starts out like that. What I'm suggesting is a slower, more disciplined approach that - hopefully - will lead to to more interest from the people you ask for help from (because the question is small and precise), and less bafflement for yourself (because it deals with one small step).