Thread: NULL POINTER EXCEPTION error

Hi, I'm writing a code for my college class. It's my second lab assignment and I'm kinda stuck in rut.
The program is to show a smiley face animating across a frame and as it hits the wall, it changes color to the color of the wall and reverse direction. Then, the wall changes to the color of the SmileyFace.
I don't know if I instantiated the objects( "movingSmiley" and "display") correctly or not.
Note: SmileyFace and SmileyDisplay are the classes my professor wrote for me already.


It keeps showing me this error.

Exception in thread "main" java.lang.NullPointerException
	at SmileyAnimation.hitBottomWall(SmileyAnimation.java:261)
	at SmileyAnimation.hitSomething(SmileyAnimation.java:113)
	at SmileyAnimation.animate(SmileyAnimation.java:90)
	at SmileyFrame.activate(SmileyFrame.java:41)
	at Smiley.main(Smiley.java:19)

This is my class from the program that I'm having trouble with:

// SmileyAnimation.java - Create and animate the smiley
//
// ICS 21: Lab Assignment 2
//
// Coded by Norman Jacobson October, 2006
// Direction constants added by Norman Jacobson, October, 2010
 
 
import java.awt.Color;				// so we can use colors
import java.util.Random;			// so we can use the random number generator
 
//	class Color color constants are
//		BLACK, BLUE, CYAN, GRAY, DARK_GRAY, LIGHT_GRAY, GREEN, MAGENTA,
//		ORANGE, PINK, RED, WHITE, YELLOW
 
 
// Panel in which smileys are drawn
public class SmileyAnimation
{
	private SmileyDisplay display;			// screen on which animation appears
	private SmileyFace movingSmiley;		// smiley that's animated
 
	// Change left to right, or up to down, or visa versa
	private static final int REVERSE_DIRECTION = -1;
 
	private static final int INIT_X_DIRECTION = 1; // Smiley starts moving to the right
	private static final int INIT_Y_DIRECTION = 0; // smiley starts moving with no vertical movement
 
	private int currentXMovement;			// 1 = right, -1 = left, 0 = no change
	private int currentYMovement;			// 1 = down, -1 = up, 0 = no change
 
	private Random generator;				// random number generator
 
	private static final long TIME_TO_RUN = 30000; // # of milliseconds to run animation
 
 
	// Make the smiley to be animated
	// Paint the starting screen
	// Set initial smiley movement
	// Initialize the random number generator
	public SmileyAnimation(SmileyDisplay d)
	{
		// *** REPLACE THIS COMMENT WITH YOUR CODE ***
		SmileyFace movingSmiley = new SmileyFace();
		SmileyDisplay display = new SmileyDisplay();
		movingSmiley.getFace().setAttributes(Color.blue, 325,325, 100, 100);
		movingSmiley.getLeftEye().setAttributes(Color.white, 305, 300, 25, 25);
		movingSmiley.getRightEye().setAttributes(Color.white, 345, 300, 25, 25);
		movingSmiley.getSmile().setAttributes(Color.magenta, 325, 350, 35, 35);
		display.setWallColor("Left", Color.GRAY);
		display.setWallColor("Right", Color.PINK);
		display.setWallColor("Top", Color.RED);
		display.setWallColor("Bottom", Color.YELLOW);
		display = d;
		currentXMovement = INIT_X_DIRECTION;
		currentYMovement = INIT_Y_DIRECTION;
		Random generator = new Random();
 
	}
 
 
	// Reeturn the smiley face
	public SmileyFace getSmileyFace()
	{
		return movingSmiley;
	}
 
 
	// Animate the smiley
	public void animate()
	{
		// Set the current time
		long startTime = System.currentTimeMillis();
 
		System.out.println("It's great.");
		// Run the animation for TIME_TO_RUN seconds
		do
		{
			// Continue to move smiley in current direction until it hits
			// an edge; when that happens, swap color of smiley
			// and wall and change direction
 
 
 
			// Use pause() as needed to "slow down" the smiley so that
			// it does not zip across the screen so fast we can't see what
			// it's doing!
 
			// *** REPLACE THIS COMMENT WITH YOUR CODE ***
			if(hitSomething() == false)
			{	getSmileyFace().translate(currentXMovement, currentYMovement);
				System.out.println("It's moving, not changing direction yet.");
			}
			else if (hitSomething() == true)
			{
				adjustColorAndDirection();
				getSmileyFace().translate(currentXMovement, currentYMovement);	
				System.out.println("It's moving, changing direction now.");
			}
			else
				System.out.println("Error, check the method, animate -> do while loop");
 
			pause(10); // pause for 10 milliseconds
			System.out.println("SmileyFace is Moved");
			display.draw(); //helps "smooth" the smileyFace translation to look as if were moving
 
		} while (System.currentTimeMillis() - startTime < TIME_TO_RUN);
	}
 
 
	// Hit something! Return true if hit any wall; false if not hit any of them
	private boolean hitSomething()
	{
		if(hitBottomWall() == true)
			return true;
		else if(hitTopWall() == true)
			return true;
		else if(hitLeftWall() == true)
			return true;
		else if(hitRightWall() == true)
			return true;
		else
			return false;
 
	}
 
 
	// Hit an edge: swap color with smiley background
	//   and move off in a new direction away from the wall
	// Use helper methods adjustColor() and adjustDirection()
	private void adjustColorAndDirection()
	{
		if(hitSomething() == true)
			if(hitBottomWall() == true)
			{	
				adjustColor("Bottom");
				adjustDirection("Bottom");
			}
			else if(hitTopWall() == true)
			{	
				adjustColor("Top");
				adjustDirection("Top");
			}
			else if(hitLeftWall() == true)
			{	
				adjustColor("Left");
				adjustDirection("Left");
			}
			else if(hitRightWall() == true)
			{	
				adjustColor("Right");
				adjustDirection("Right");
			}
			else
				System.out.println("Error, check the method, adjustColorAndDirection");
 
	}
 
 
	// Swap the colors of the wallHit wall and the smiley
	// wallHit can be "Left", "Right", "Top", or "Bottom",
	//  these strings corresponding to the walls they name
	private void adjustColor(String wallHit)
	{
		Color wall = display.getWallColor(wallHit);
		display.setWallColor(wallHit, movingSmiley.getFace().getColor());
		movingSmiley.getFace().setColor(wall);
 
	}
 
 
	// Change the smiley's direction so it is away from
	// the wall just hit.
	// wallHit can be "Left", "Right", "Top", or "Bottom",
	//  these strings corresponding to the walls they name
	private void adjustDirection(String wallHit)
	{
		// If hit top or bottom wall, y direction is reversed,
		// x direction can be to the left, to the right, or
		// no movement at all (translation of 0); it is randomly
		// chosen
 
		// If hit left or right wall, x direction is reversed,
		// y direction can be up, down, or no movement
		// (translation of 0); it is randomly chosen
 
		// *** REPLACE THIS COMMENT WITH YOUR CODE ***
		if(wallHit == "Botton" || wallHit == "Top" )
		{	
			currentYMovement = currentYMovement * REVERSE_DIRECTION;
			currentXMovement = currentXMovement * (generator.nextInt(3) - 1);
		}	
		else if(wallHit == "Left" || wallHit == "Right")
		{	
			currentXMovement = currentXMovement * REVERSE_DIRECTION;
			currentYMovement = currentYMovement * (generator.nextInt(3) - 1);
		}
		else
			System.out.println("Error, Check the method called, adjustDirection -> else");
 
	}
 
 
	// Return true if hit left wall, false otherwise
	private boolean hitLeftWall()
	{
		// Hit wall if x coordinate of leftmost point of smiley is
		// same or less than edge of the left wall,
		// and the smiley is moving toward this wall
 
 
		// *** REPLACE THIS COMMENT WITH YOUR CODE ***
		if(getSmileyFace().getLeftEdge() <= display.getEdge("Left"))
			return true;
		else
			return false;
 
	}
 
 
	// Return true if hit right wall, false otherwise
	private boolean hitRightWall()
	{
		// Hit wall if x coordinate of rightmost point of smiley is
		// same or greater than edge of the right wall,
		// and the smiley is moving toward this wall
 
 
		// *** REPLACE THIS COMMENT WITH YOUR CODE ***
		if(getSmileyFace().getRightEdge() >= display.getEdge("Right"))
			return true;
		else
			return false;
	}
 
 
	// Return true if hit top wall, false otherwise
	private boolean hitTopWall()
	{
		// Hit wall if y coordinate of top-most point of smiley is
		// same or less than edge of the top wall,
		// and the smiley is moving toward this wall
 
 
		// *** REPLACE THIS COMMENT WITH YOUR CODE ***
		if(getSmileyFace().getTopEdge() <= display.getEdge("Top"))
			return true;
		else
			return false;
	}
 
 
	// Return true if hit bottom wall, false otherwise
	private boolean hitBottomWall()
	{
		// Hit wall if y coordinate of bottom-most point of smiley is
		// same or greater than edge of the bottom wall,
		// and the smiley is moving toward this wall
 
 
		// *** REPLACE THIS COMMENT WITH YOUR CODE ***
		if (getSmileyFace().getBottomEdge() >= display.getEdge("Bottom"))
			return true;
		else
			return false;
	}
 
	// Wait x milliseconds before moving to next animation frame
	private void pause(long millisec)
	{
		long startTime = System.currentTimeMillis();
		long endTime;
		do
		{
			endTime = System.currentTimeMillis();
		} while (endTime - startTime < millisec);
	}
 
}

Lab Assignment Manual from the professor's Website

In the constructor, change the line:

SmileyDisplay display = new SmileyDisplay();
//with
display = new SmileyDisplay();

because you already declared the display object above.

application context