Thread: Please Help Me With This Error!

Hi, I have attempted to make a puzzle game where you get a broken up puzzle and you need to solve it with the various pieces.

I keep getting this error. I have no clue as to why I am getting this error. I searched on google to see what it means and I figured it out that it is different for every situation
here is the error:
java.lang.NullPointerException
at Puzzle.init(Puzzle.java:57)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

I also believe it cannot get the images width correctly for some odd reason

import java.applet.Applet;
import java.awt.*;
import java.awt.image.*;
import java.util.*;

public class Puzzle extends Applet
{
private final boolean debug = false;

private boolean secondClick = false;

private final int pref = 72; // prefered tile size

private int firstCol = -1;
private int firstRow = -1;

private int pieceWidth;
private int pieceHeight;

private int puzzleWidth;
private int puzzleHeight;

private int maxCol;
private int maxRow;

private int correct;
private int moves;

private int[][] layout;

private Image[] piece;

private Image imageBuffer;
private Graphics graphicsBuffer;

public void init()
{
moves = correct = 0;

MediaTracker mt;

Image source = getImage( getDocumentBase(), getParameter( "mario.jpg" ) );

mt = new MediaTracker( this );
mt.addImage( source, 0 );
try { mt.waitForID( 0 ); } catch( InterruptedException e ){}

debug( "Calculating dimensions..." );
puzzleWidth = source.getWidth( this );
puzzleHeight = source.getHeight( this );

debug( "Image is " + puzzleWidth + " by " + puzzleHeight );

maxCol = ( puzzleWidth / pref ) + 1;
maxRow = ( puzzleHeight / pref ) + 1;

debug( "Optimal grid is " + maxCol + " by " + maxRow );
layout = new int[ maxRow ][ maxCol ];
int len = maxCol * maxRow;

piece = new Image[ len ];
pieceWidth = puzzleWidth / maxCol;
pieceHeight = puzzleHeight / maxRow;

debug( "Each piece will be " + pieceWidth
+ " by " + pieceHeight + " pixels" );
int mpw = maxCol * pieceWidth;
int mph = maxRow * pieceHeight;

imageBuffer = createImage( mpw, mph );
graphicsBuffer = imageBuffer.getGraphics();

debug( "Extracting pieces..." );
mt = new MediaTracker( this );
int row, col;
for( row = 0; row < maxRow; row++ )
{
for( col = 0; col < maxCol; col++ )
{
CropImageFilter cif = new CropImageFilter( col * pieceWidth,
row * pieceHeight,
pieceWidth,
pieceHeight );
ImageProducer ip = source.getSource();
ip = new FilteredImageSource( ip, cif );
int num = ( row * maxCol ) + col;
layout[ row ][ col ] = -1;
piece[ num ] = createImage( ip );
mt.addImage( piece[ num ], 0 );
try { mt.waitForID( 0 ); } catch( InterruptedException e ){}
}
}
debug( "Randomizing layout..." );
row = col = 0;
Random r = new Random();
r.setSeed( System.currentTimeMillis() );

// TODO: find a better [faster] randomization method!
for( int i = 0; i < len; i++ )
{
col = Math.abs( r.nextInt() % maxCol );
row = Math.abs( r.nextInt() % maxRow );

while( layout[ row ][ col ] != -1 )
{
col += 1;

if( col >= maxCol )
{
row += 1;
row %= maxRow;
col = 0;
}
}

layout[ row ][ col ] = i;

if( ( ( row * maxCol ) + col ) == i )
{
correct += 1;
}
}
repaint();
}

public void paint( Graphics g )
{
int pwb = pieceWidth;
int phb = pieceHeight;

debug( "Drawing the screen..." );
for( int row = 0; row < maxRow; row++ )
{
for( int col = 0; col < maxCol; col++ )
{
graphicsBuffer.drawImage( piece[ layout[ row ][ col ] ],
col * pwb,
row * phb,
this );
}
}
if( secondClick )
{
graphicsBuffer.setColor( Color.red );
graphicsBuffer.drawRect( firstCol * pwb,
firstRow * phb,
pieceWidth - 1,
pieceHeight - 1 );
graphicsBuffer.drawRect( firstCol * pwb + 2,
firstRow * phb + 2,
pieceWidth - 5,
pieceHeight - 5 );
graphicsBuffer.setColor( Color.pink );
graphicsBuffer.drawRect( firstCol * pwb + 1,
firstRow * phb + 1,
pieceWidth - 3,
pieceHeight - 3 );
}
g.drawImage( imageBuffer, 0, 0, this );
}

public boolean mouseDown( Event e, int a, int b )
{
int col = ( a / pieceWidth );
int row = ( b / pieceHeight );

if( ( col < maxCol ) && ( row < maxRow ) )
{
debug( "User clicked on piece " + col + ", " + row );

if( layout[ row ][ col ] == ( ( row * maxCol ) + col ) )
{
// beep?
}
else
{
if( secondClick )
{
int secondPiece = layout[ row ][ col ];
int firstPiece = layout[ firstRow ][ firstCol ];

debug( "Swapping piece " + secondPiece
+ " with " + firstPiece );

layout[ firstRow ][ firstCol ] = secondPiece;
layout[ row ][ col ] = firstPiece;

secondClick = false;

if( ( ( row * maxCol ) + col ) == firstPiece )
{
correct += 1;
}

if( ( ( firstRow * maxCol ) + firstCol ) == secondPiece )
{
correct += 1;
}

if( firstPiece != secondPiece )
{
moves += 1;
}
}
else
{
firstRow = row;
firstCol = col;
secondClick = true;
}
repaint();
}
return true;
}
else
{
return false;
}
}

private void debug( String s )
{
if( debug )
{
System.out.println( "[Puzzle] " + s );
}
}

First of all, a NullPointerException occurs when an object is Null, meaning it has no value, and you are trying to do something with it. Since the error occurs at line 57, there is something wrong with this line of code:

debug( "Optimal grid is " + maxCol + " by " + maxRow );

So, let's go through a checklist to pinpoint the problem.
1) Does the debug method work as intended in the previous calls (For example, line 52?)

--> If it works as intended in line 52, then there is something wrong with the following operations

maxCol = ( puzzleWidth / pref ) + 1;
maxRow = ( puzzleHeight / pref ) + 1;

And since the code on line 52 works properly, this means that the pref variable is probably not initialized. However, pref is a final variable and is initialized, so the problem wouldn't be with the pref variable.

What line does your IDE highlight when it shows you the error? What is the code of that line?

Something must be null.

Either one, or both, of your two variables must be null. Why it's doing that is a mystery, as it should let you pass a null value as a param String. However, maybe you do something else with the String that is causing the error.

Use try/catch blocks on the two variables used in the debug() call and have it pirnt out something for each to see which, if either, is null.

It would help out a whole lot if you actually pointed us to what line 57 is

Originally Posted by Parranoia

It would help out a whole lot if you actually pointed us to what line 57 is

It appears to be:

debug( "Optimal grid is " + maxCol + " by " + maxRow );

if you copy and paste it directly into there.

Id like to start off by thanking everyone for their time in helping me. The line that is highlighted when im attempting to run is:

puzzleWidth = source.getWidth (this); (Line 55)

Check and see if source is null.

I don't exactly understand what you mean. If you mean that if the source height and width of the image are coming up as null, then yes the source is null.

Thanks a lot! We got the programming working