most of the graphic components are commented out, I was just trying to implement an interface using gridBagLayout. Can someone tell me why the following code compiles good but returns a nullPointer exception when I run it. I sure would appreciate it, anything that can be added is ALWAYS appreciated. thankyou in advance!
// Fig. 10.21: DeckOfCards.java
// Card shuffling and dealing program
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
publicclass DeckOfCards extends JFrame {
private Card deck[];
private Card myHand[];
private Card hisHand[];
privateint currentCard;
private JButton dealButton, shuffleButton, discardButton;
private JTextField mDisplayCard1,mDisplayCard2,mDisplayCard3,mDisplayCard4,mDisplayCard5;
private JTextField hDisplayCard1,hDisplayCard2,hDisplayCard3,hDisplayCard4,hDisplayCard5;
private JLabel status, dealerTag, playerTag;
// put private .gif actualCards[]; here
privateint mCountFaces[];
privateint mCountSuits[];
privateint hCountFaces[];
privateint hCountSuits[];
private JPanel buttonPanel;
private JPanel buttonPanel2;
private JPanel buttonPanel3;
// private Image logo1;
private GridBagLayout gbLayout;
private GridBagConstraints gbConstraints;
private Container container;
public DeckOfCards()
{
super( "Card Dealing Program" );
String faces[] = { "Ace", "Deuce", "Three", "Four",
"Five", "Six", "Seven", "Eight",
"Nine", "Ten", "Jack", "Queen",
"King" };
String suits[] = { "Hearts", "Diamonds",
"Clubs", "Spades" };
// set up counting arrays
//these will be used by comparing string values of the cards and then adding
// one to their position in the array, can then analyze the array to
// determine what we have in our hands. the suits array is for calculating flushes
mCountFaces = newint[13];
mCountSuits = newint[4];
// his counting arrays
hCountFaces = newint[13];
hCountSuits = newint[4];
deck = new Card[ 52 ];
// hold MY cards
myHand = new Card[ 5 ];
// hold his cards
hisHand = new Card[ 5 ];
currentCard = -1;
for ( int i = 0; i < deck.length; i++ )
deck[ i ] = new Card( faces[ i % 13 ],
suits[ i / 13 ],i );
container = getContentPane();
gbLayout = new GridBagLayout();
container.setLayout( gbLayout );
dealerTag.setText("Dealer" );
playerTag.setText("Player 1");
gbConstraints.fill = GridBagConstraints.BOTH;
addComponent(dealerTag,1,3,1,1);
dealButton = new JButton( "Deal card" );
dealButton.addActionListener(
new ActionListener() {
publicvoid actionPerformed( ActionEvent e )
{
Card mDealt1 = dealCard();
if ( mDealt1 != null ) {
mDisplayCard1.setText( mDealt1.toString() );
myHand[0] = mDealt1;
}
else {
mDisplayCard1.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card hDealt1 = dealCard();
if ( hDealt1 != null ) {
hDisplayCard1.setText( hDealt1.toString() );
hisHand[0] = hDealt1;
}
else {
hDisplayCard1.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card mDealt2 = dealCard();
if ( mDealt2 != null ) {
mDisplayCard2.setText( mDealt2.toString() );
myHand[1] = mDealt2;
}
else {
mDisplayCard2.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card hDealt2 = dealCard();
if ( hDealt2 != null ) {
hDisplayCard2.setText( hDealt2.toString() );
hisHand[1] = hDealt2;
}
else {
hDisplayCard2.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card mDealt3 = dealCard();
if ( mDealt3 != null ) {
mDisplayCard3.setText( mDealt3.toString() );
myHand[2] = mDealt3;
}
else {
mDisplayCard3.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card hDealt3 = dealCard();
if ( hDealt3 != null ) {
hDisplayCard3.setText( hDealt3.toString() );
hisHand[2] = hDealt3;
}
else {
hDisplayCard3.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card mDealt4 = dealCard();
if ( mDealt4 != null ) {
mDisplayCard4.setText( mDealt4.toString() );
myHand[3] = mDealt4;
}
else {
mDisplayCard4.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card hDealt4 = dealCard();
if ( hDealt4 != null ) {
hDisplayCard4.setText( hDealt4.toString() );
hisHand[3] = hDealt4;
}
else {
hDisplayCard4.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card mDealt5 = dealCard();
if ( mDealt5 != null ) {
mDisplayCard5.setText( mDealt5.toString() );
myHand[4] = mDealt5;
}
else {
mDisplayCard5.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
Card hDealt5 = dealCard();
if ( hDealt5 != null ) {
hDisplayCard5.setText( hDealt5.toString() );
hisHand[4] = hDealt5;
}
else {
hDisplayCard5.setText(
"NO MORE CARDS TO DEAL" );
status.setText(
"Shuffle cards to continue" );
}
// this is just a test to print out to the console
for(int tempx = 0;tempx<5;tempx++){
System.out.println(myHand[tempx].toString());
}
// this is just a test to print out to the console
for(int tempy = 0;tempy<5;tempy++){
System.out.println(hisHand[tempy].toString());
}
}
}
);
dealButton.setEnabled(false);
//c.add(dealButton);
discardButton = new JButton( "Discard" );
discardButton.addActionListener(
new ActionListener() {
publicvoid actionPerformed( ActionEvent e )
{
// put functionality for discard here
System.out.println("discarded");
}
}
);
//c.add(discardButton);
shuffleButton = new JButton( "Shuffle cards" );
shuffleButton.addActionListener(
new ActionListener() {
publicvoid actionPerformed( ActionEvent e )
{
mDisplayCard1.setText( "SHUFFLING ..." );
shuffle();
mDisplayCard1.setText( "DECK IS SHUFFLED" );
mDisplayCard2.setText( " " );
mDisplayCard3.setText( " " );
mDisplayCard4.setText( " " );
mDisplayCard5.setText( " " );
hDisplayCard1.setText( " " );
hDisplayCard2.setText( " " );
hDisplayCard3.setText( " " );
hDisplayCard4.setText( " " );
hDisplayCard5.setText( " " );
}
}
);
//c.add(shuffleButton);
mDisplayCard1 = new JTextField( 15 );
mDisplayCard1.setEditable( false );
//c.add( mDisplayCard1);
hDisplayCard1 = new JTextField( 15 );
hDisplayCard1.setEditable( false );
//c.add(hDisplayCard1);
mDisplayCard2 = new JTextField( 15 );
mDisplayCard2.setEditable( false );
//c.add( mDisplayCard2);
hDisplayCard2 = new JTextField( 15 );
hDisplayCard2.setEditable( false );
//c.add( hDisplayCard2);
mDisplayCard3 = new JTextField( 15 );
mDisplayCard3.setEditable( false );
//c.add( mDisplayCard3 );
hDisplayCard3 = new JTextField( 15 );
hDisplayCard3.setEditable( false );
//c.add( hDisplayCard3);
mDisplayCard4 = new JTextField( 15 );
mDisplayCard4.setEditable( false );
//c.add( mDisplayCard4 );
hDisplayCard4 = new JTextField( 15 );
hDisplayCard4.setEditable( false );
//c.add( hDisplayCard4);
mDisplayCard5 = new JTextField( 15 );
mDisplayCard5.setEditable( false );
//c.add( mDisplayCard5);
hDisplayCard5 = new JTextField( 15 );
hDisplayCard5.setEditable( false );
//c.add( hDisplayCard5);
status = new JLabel();
//c.add( status );
setSize( 400,400); // set the window size
show(); // show the window
}
publicvoid shuffle()
{
currentCard = -1;
for ( int i = 0; i < deck.length; i++ ) {
int j = ( int ) ( Math.random() * 52 );
Card temp = deck[ i ]; // swap
deck[ i ] = deck[ j ]; // the
deck[ j ] = temp; // cards
}
dealButton.setEnabled( true );
}
public Card dealCard()
{
if ( ++currentCard < deck.length )
return deck[ currentCard ];
else {
dealButton.setEnabled( false );
returnnull;
}
}
publicvoid findOnePair(){}
publicvoid findTwoPair(){}
publicvoid findThreeOfAKind(){}
publicvoid findFourOfAKind(){}
publicvoid findFlush(){}
publicvoid findStraight(){}
publicvoid findFullhouse(){}
privatevoid addComponent(Component c, int row, int column, int width, int height){
gbConstraints.gridx = column;
gbConstraints.gridy = row;
gbConstraints.gridwidth = width;
gbConstraints.gridheight = height;
gbLayout.setConstraints(c,gbConstraints);
container.add(c);
}
publicstaticvoid main( String args[] )
{
DeckOfCards app = new DeckOfCards();
app.addWindowListener(
new WindowAdapter() {
publicvoid windowClosing( WindowEvent e )
{
System.exit( 0 );
}
}
);
}
}
class Card {
private String face;
private String suit;
privateint rep;
public Card( String f, String s, int r )
{
face = f;
suit = s;
rep = r;
}
public String toString() { return face + " of " + suit; }
}
Never mind, I figured out that I was trying to use a graphic object (gbConstraints) without instantiating it first... thanks anyway! I was just having problems with understanding JAVAC since it doesnt give good error info!
From looking at your code you know alot about java so odds are this may not be the problem. I found from experience that most null pointer exceptions comes from not initializing objects. If you use an object that don't have an assigned value to it then it will cause a null pointer exception displayed even though it compiles. This is the hardest situation to find thats why I think that this may cause your exception. Check all objects and make sure that you don't use an object to call a method that hasn't been fully initialized. That's the only advice I can tell you hope it helps.
You guys are losing me in this discussion. Seems to me that the easiest solution is to look at the exception stack trace. More importantly, when you post a "why am I getting an XException" type of question, please include the stack trace.
For example, I could post this incredibly stimulating piece of software technology:
and say that there is a NullPointerExceptoin when I run it. Then, you'd be forced to pore over the source code for hours trying to find out why. Or I could be kinder and also include the output of the program:
Exception in thread "main" java.lang.NullPointerException at Hello.main(Hello.java:16)
With this valuable information, you'd be able to spot the problem in a jiffy. What do you think the chances are it is somewhere in the neighborhood of line 16 in Hello.java?
Matt I really appreciate your feedback, at least to me, between you and SMETS, you guys provide the bulk of the best answers here. I simply did not include the stack for 2 reasons, first of all I didnt appreciate the value of it. I didnt understand how to read it when it is usually more than just the one line long. also, I assumed that since I included the complete source that you could do a cut/paste and compile it for yourself quite possibly using a better debugger... sorry for the inconvenience... by the way, I did figure this out, but could not pull the topic before i got responses. thanks anyway
Sorry, I just can't resist the occasional opportunity to indulge in sarcasm. ;-)
Seriously, though, it is pretty common that people post code and say that there is some exception, but don't post the exception information. The copy/past option is time-consuming and doesn't often work (particularly when someone is using a particular environment like JBuilder or BlueJ that imports special packages).
That's why I wanted to emphasize the importance of that, not just for you, but for everyone posting questions.
Maybe we need a little "Posting Tips" list right at the top of the forum that suggests what information to include and also suggests using the "Formatting Your Post" tags. Those tags are described at the bottom of the page, where I think most people don't notice them.
well I most definitely got the hint! since I use DOS to compile my stuff still, it is not easy to get the stack info since I can't just copy it. but dont worry, that wont stop me now! :) I will figure something out! thanks again for stopping by to look at my stuff. Obviously, I saw the tag stuff, but yes a general hints section authored mainly by the main people who do respond and know what they need to respond efficiently would be a very good idea. anyway, keep up the good work! L8R
If you are compiling in a DOS box or "Command Prompt" in Windows, you can copy from it by clicking on the Window's icon on the upper left and selecting "Edit/Mark" (the particulars of this varies slightly depending upon the Windows version, but they all have it).
In an NT/Win2k/XP command shell, you can run your program like this: "java MyProg 2>output.txt" and that will redirect the error output to the output.txt file.
If you are really on DOS only it can be done, too, but we won't go into that, for the follwing reason: I doubt you are woking in real DOS, since Javac.exe is a Windows console application (I just did a hex dump of it to check) and only says "This program cannot be run in DOS mode" under DOS.
Previous Topic
