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Thread: NULL POINTER EXCEPTION error

  1. #1
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    Exclamation 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
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    Last edited by beefwithrice; October 26th, 2011 at 02:05 PM.


  2. #2
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    Default Re: NULL POINTER EXCEPTION error

    In the constructor, change the line:
    SmileyDisplay display = new SmileyDisplay();
    //with
    display = new SmileyDisplay();
    because you already declared the display object above.

    application context
    Last edited by daniel.j2ee; December 13th, 2011 at 04:03 PM.

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    Default Re: NULL POINTER EXCEPTION error

    Quote Originally Posted by daniel.j2ee View Post
    In the constructor, change the line:
    SmileyDisplay display = new SmileyDisplay();
    //with
    display = new SmileyDisplay();
    because you already declared the display object above.
    You must read the stacktrace...

    @beefwithrice: I guess stack trace is descriptive enough to take you to the root.

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