Log4j within an abstract class error

I'm trying to build/implement my first abstract class. When I attempt to run it I get the following error.
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/log4j/Logger at BBSDDE.<clinit>(BBSDDE.java:91)
BBSDDE is the abstract class I am trying to extend.
On line 91 of BBSDDE.java is
     static Logger logger = Logger.getLogger(BBSDDE.class) ;
I have included
     import org.apache.log4j.Logger;
     import org.apache.log4j.PropertyConfigurator;
As part of the class that extends BBSDDE (Sample.java) I have in the constructor to
     PropertyConfigurator.configure(logfile);
     (Logfile is valid at this stage)
I have also tried to .configure from the Sample.java with the same error?

Copy of the configuration file
log4j.rootLogger=debug, stdout, R
#log4j.rootLogger=info, stdout, R
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
# Pattern to output the caller's file name and line number.
log4j.appender.stdout.layout.ConversionPattern=%d %5p [%t] (%F:%L) - %m%n
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=../logs/sample.log
log4j.appender.R.MaxFileSize=1024KB
# Keep one backup file
log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d %5p [%t] (%F:%L) %c - %m%n

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    In this section we will redesign our OneRowNim game to fit within a hierarchy of classes of two-player games. There are many games that characteristically involve two players: checkers, chess, tic-tac-toe, guessing games, and so forth. However, there are also many games that involve just one player: blackjack, solitaire, and others. There are also games that involve two or more players, such as many card games. Thus, our redesign of OneRowNim as part of a two-player game hierarchy will not be our last effort to design a hierarchy of game-playing classes. We will certainly redesign things as we learn new Java language constructs and as we try to extend our game library to other kinds of games.
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    One of our design goals is to revise the OneRowNim game so that it fits into a hierarchy of two-player games. One way to do this is to generalize the OneRowNim game by creating a superclass that contains those attributes and methods that are common to all two-player games. The superclass will define the most general and generic elements of two-player games. All two-player games, including OneRowNim, will be defined as subclasses of this top-level superclass and will inherit and possibly override its public and protected variables and methods. Also, our top-level class will contain certain abstract methods, whose implementations will be given in OneRowNim and other subclasses.
    Generic superclass
    A second goal is to design a class hierarchy that makes it possible for computers to play the game, as well as human users. Thus, for a given two-player game, it should be possible for two humans to play each other, or for two computers to play each other, or for a human to play against a computer. This design goal will require that our design exhibit a certain amount of flexibility. As we shall see, this is a situation in which Java interfaces will come in handy.
    [Page 376]
    Another important goal is to design a two-player game hierarchy that can easily be used with a variety of different user interfaces, including command-line interfaces and GUIs. To handle this feature, we will develop Java interfaces to serve as interfaces between our two-player games and various user interfaces.
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    Figure 8.18. The current OneRowNim class.
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    [Page 377]
    Constructors are not inherited
    Given these considerations, we come up with the design shown in Figure 8.19. The design shown in this figure is much more complex than the designs used in earlier chapters. However, the complexity comes from combining ideas already discussed in previous sections of this chapter, so don't be put off by it.
    Figure 8.19. TwoPlayerGame is the superclass for OneRowNim and other two-player games.
    To begin with, note that we have introduced two Java interfaces into our design in addition to the TwoPlayerGame superclass. As we will show, these interfaces lead to a more flexible design and one that can easily be extended to incorporate new two-player games. Let's take each element of this design separately.
    [Page 378]
    8.6.3. The TwoPlayerGame Superclass
    As we have stated, the purpose of the TwoPlayerGame class is to serve as the superclass for all two-player games. Therefore, it should define the variables and methods shared by two-player games.
    The PLAYER_ONE, PLAYER_TWO, and onePlaysNext variables and the getPlayer(), setPlayer(), and changePlayer() methods have been moved up from the OneRowNim class. Clearly, these variables and methods apply to all two-player games. Note that we have also added three new variables, nComputers, computer1, computer2, and their corresponding methods, getNComputers() and addComputerPlayer(). We will use these elements to give our games the capability to be played by computer programs. Because we want all of our two-player games to have this capability, we define these variables and methods in the superclass rather than in OneRowNim and subclasses of TwoPlayerGame.
    Note that the computer1 and computer2 variables are declared to be of type IPlayer. IPlayer is an interface containing a single method declaration, the makeAMove() method:
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    Why do we use an interface here rather than some type of game-playing object? This is a good design question. Using an interface here makes our design more flexible and extensible because it frees us from having to know the names of the classes that implement the makeAMove() method. The variables computer1 and computer2 will be assigned objects that implement IPlayer via the addComputerPlayer() method.
    Game-dependent algorithms
    The algorithms used in the various implementations of makeAMove() are game-dependentthey depend on the particular game being played. It would be impossible to define a game playing object that would suffice for all two-player games. Instead, if we want an object that plays OneRowNim, we would define a OneRowNimPlayer and have it implement the IPlayer interface. Similarly, if we want an object that plays checkers, we would define a CheckersPlayer and have it implement the IPlayer interface. By using an interface here, our TwoPlayerGame hierarchy can deal with a wide range of differently named objects that play games, as long as they implement the IPlayer interface. Using the IPlayer interface adds flexibility to our game hierarchy and makes it easier to extend it to new, yet undefined, classes. We will discuss the details of how to design a game player in Section 8.6.7.
    The IPlayer interface
    Turning now to the methods defined in TwoPlayerGame, we have already seen implementations of getPlayer(), setPlayer(), and changePlayer() in the OneRowNim class. We will just move those implementations up to the superclass. The getNComputers() method is the assessor method for the nComputers variable, and its implementation is routine. The addComputerPlayer() method adds a computer player to the game. Its implementation is as follows:
    [Page 379]
    public void addComputerPlayer(IPlayer player) {
    if (nComputers == 0)
    computer2 = player;
    else if (nComputers == 1)
    computer1 = player;
    else
    return; // No more than 2 players
    ++nComputers;
    As we noted earlier, the classes that play the various TwoPlayerGames must implement the IPlayer interface. The parameter for this method is of type IPlayer. The algorithm we use checks the current value of nComputers. If it is 0, which means that this is the first IPlayer added to the game, the player is assigned to computer2. This allows the human user to be associated with PLAYERONE if this is a game between a computer and a human user.
    If nComputers equals 1, which means that we are adding a second IPlayer to the game, we assign that player to computer1. In either of these cases, we increment nComputers. Note what happens if nComputers is neither 1 nor 2. In that case, we simply return without adding the IPlayer to the game and without incrementing nComputers. This, in effect, limits the number of IPlayers to two. (A more sophisticated design would throw an exception to report an error. but we will leave that for a subsequent chapter.)
    The addComputerPlayer() method is used to initialize a game after it is first created. If this method is not called, the default assumption is that nComputers equals zero and that computer1 and computer2 are both null. Here's an example of how it could be used:
    OneRowNim nim = new OneRowNim(11); // 11 sticks
    nim.add(new NimPlayer(nim)); // 2 computer players
    nim.add(new NimPlayerBad(nim));
    Note that the NimPlayer() constructor takes a reference to the game as its argument. Clearly, our design should not assume that the names of the IPlayer objects would be known to the TwoPlayerGame superclass. This method allows the objects to be passed in at runtime. We will discuss the details of NimPlayerBad in Section 8.6.7.
    The getrules() method is a new method whose purpose is to return a string that describes the rules of the particular game. This method is implemented in the TwoPlayerGame class with the intention that it will be overridden in the various subclasses. For example, its implementation in TwoPlayerGame is:
    public String getRules() {
    return "The rules of this game are: ";
    Overriding a method
    [Page 380]
    and its redefinition in OneRowNim is:
    public String getRules() {
    return "\n*** The Rules of One Row Nim ***\n" +
    "(1) A number of sticks between 7 and " + MAX_STICKS +
    " is chosen.\n" +
    "(2) Two players alternate making moves.\n" +
    "(3) A move consists of subtracting between 1 and\n\t" +
    MAX_PICKUP +
    " sticks from the current number of sticks.\n" +
    "(4) A player who cannot leave a positive\n\t" +
    " number of sticks for the other player loses.\n";
    The idea is that each TwoPlayerGame subclass will take responsibility for specifying its own set of rules in a form that can be displayed to the user.
    You might recognize that defining geTRules() in the superclass and allowing it to be overridden in the subclasses is a form of polymorphism. It follows the design of the toString() method, which we discussed earlier. This design will allow us to use code that takes the following form:
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    In this example the call to getrules() is polymorphic. The dynamic-binding mechanism is used to invoke the getrules() method defined in the OneRowNim class.
    The remaining methods in TwoPlayerGame are defined abstractly. The gameOver() and getWinner() methods are both game-dependent methods. That is, the details of their implementations depend on the particular TwoPlayerGame subclass in which they are implemented.
    This is good example of how abstract methods should be used in designing a class hierarchy. We give abstract definitions in the superclass and leave the detailed implementations up to the individual subclasses. This allows the different subclasses to tailor the implementations to their particular needs, while allowing all subclasses to share a common signature for these tasks. This enables us to use polymorphism to create flexible, extensible class hierarchies.
    Figure 8.20 shows the complete implementation of the abstract TwoPlayerGame class. We have already discussed the most important details of its implementation.
    Figure 8.20. The TwoPlayerGame class
    (This item is displayed on page 381 in the print version)
    public abstract class TwoPlayerGame {
    public static final int PLAYER_ONE = 1;
    public static final int PLAYER_TWO = 2;
    protected boolean onePlaysNext = true;
    protected int nComputers = 0; // How many computers
    // Computers are IPlayers
    protected IPlayer computer1, computer2;
    public void setPlayer(int starter) {
    if (starter == PLAYER_TWO)
    onePlaysNext = false;
    else onePlaysNext = true;
    } // setPlayer()
    public int getPlayer() {
    if (onePlaysNext)
    return PLAYER_ONE;
    else return PLAYER_TWO;
    } // getPlayer()
    public void changePlayer() {
    onePlaysNext = !onePlaysNext;
    } // changePlayer()
    public int getNComputers() {
    return nComputers;
    } // getNComputers()
    public String getRules() {
    return "The rules of this game are: ";
    } // getRules()
    public void addComputerPlayer(IPlayer player) {
    if (nComputers == 0)
    computer2 = player;
    else if (nComputers == 1)
    computer1 = player;
    else
    return; // No more than 2 players
    ++nComputers;
    } // addComputerPlayer()
    public abstract boolean gameOver(); // Abstract Methods
    public abstract String getWinner();
    } // TwoPlayerGame class
    Effective Design: Abstract Methods
    Abstract methods allow you to give general definitions in the superclass and leave the implementation details to the different subclasses.
    [Page 381]
    8.6.4. The CLUIPlayableGame Interface
    We turn now to the two interfaces shown in Figure 8.19. Taken together, the purpose of these interfaces is to create a connection between any two-player game and a command-line user interface (CLUI). The interfaces provide method signatures for the methods that will implement the details of the interaction between a TwoPlayerGame and a UserInterface. Because the details of this interaction vary from game to game, it is best to leave the implementation of these methods to the games themselves.
    Note that CLUIPlayableGame extends the IGame interface. The IGame interface contains two methods that are used to define a standard form of communication between the CLUI and the game. The getGamePrompt() method defines the prompt used to signal the user for a move of some kindfor example, "How many sticks do you take (1, 2, or 3)?" And the reportGameState() method defines how the game will report its current statefor example, "There are 11 sticks remaining." CLUIPlayableGame adds the play() method to these two methods. As we will see shortly, the play() method contains the code that will control the playing of the game.
    [Page 382]
    Extending an interface
    The source code for these interfaces is very simple:
    public interface CLUIPlayableGame extends IGame {
    public abstract void play(UserInterface ui);
    public interface IGame {
    public String getGamePrompt();
    public String reportGameState();
    } // IGame
    Note that the CLUIPlayableGame interface extends the IGame interface. A CLUIPlayableGame is a game that can be played through a CLUI. The purpose of its play() method is to contain the game-dependent control loop that determines how the game is played via a user interface (UI). In pseudocode, a typical control loop for a game would look something like the following:
    Initialize the game.
    While the game is not over
    Report the current state of the game via the UI.
    Prompt the user (or the computer) to make a move via the UI.
    Get the user's move via the UI.
    Make the move.
    Change to the other player.
    The play loop sets up an interaction between the game and the UI. The UserInterface parameter allows the game to connect directly to a particular UI. To allow us to play our games through a variety of UIs, we define UserInterface as the following Java interface:
    public interface UserInterface {
    public String getUserInput();
    public void report(String s);
    public void prompt(String s);
    Any object that implements these three methods can serve as a UI for one of our TwoPlayerGames. This is another example of the flexibility of using interfaces in object-oriented design.
    To illustrate how we use UserInterface, let's attach it to our KeyboardReader class, thereby letting a KeyboardReader serve as a CLUI for TwoPlayerGames. We do this simply by implementing this interface in the KeyboardReader class, as follows:
    public class KeyboardReader implements UserInterface
    [Page 383]
    As it turns out, the three methods listed in UserInterface match three of the methods in the current version of KeyboardReader. This is no accident. The design of UserInterface was arrived at by identifying the minimal number of methods in KeyboardReader that were needed to interact with a TwoPlayerGame.
    Effective Design: Flexibility of Java Interfaces
    A Java interface provides a means of associating useful methods with a variety of different types of objects, leading to a more flexible object-oriented design.
    The benefit of defining the parameter more generally as a UserInterface instead of as a KeyboardReader is that we will eventually want to allow our games to be played via other kinds of command-line interfaces. For example, we might later define an Internet-based CLUI that could be used to play OneRowNim among users on the Internet. This kind of extensibilitythe ability to create new kinds of UIs and use them with TwoPlayerGamesis another important design feature of Java interfaces.
    Generality principle
    Effective Design: Extensibility and Java Interfaces
    Using interfaces to define useful method signatures increases the extensibility of a class hierarchy.
    As Figure 8.19 shows, OneRowNim implements the CLUIPlayableGame interface, which means it must supply implementations of all three abstract methods: play(), getGamePrompt(), and reportGameState().
    8.6.5. Object-Oriented Design: Interfaces or Abstract Classes?
    Why are these methods defined in interfaces? Couldn't we just as easily define them in the TwoPlayerGame class and use inheritance to extend them to the various game subclasses? After all, isn't the net result the same, namely, that OneRowNim must implement all three methods.
    These are very good design questions, exactly the kinds of questions one should ask when designing a class hierarchy of any sort. As we pointed out in the Animal example earlier in the chapter, you can get the same functionality from an abstract interface and an abstract superclass method. When should we put the abstract method in the superclass, and when does it belong in an interface? A very good discussion of these and related object-oriented design issues is available in Java Design, 2nd Edition, by Peter Coad and Mark Mayfield (Yourdan Press, 1999). Our discussion of these issues follows many of the guidelines suggested by Coad and Mayfield.
    Interfaces vs. abstract methods
    We have already seen that using Java interfaces increases the flexibility and extensibility of a design. Methods defined in an interface exist independently of a particular class hierarchy. By their very nature, interfaces can be attached to any class, and this makes them very flexible to use.
    Flexibility of interfaces
    Another useful guideline for answering this question is that the superclass should contain the basic common attributes and methods that define a certain type of object. It should not necessarily contain methods that define certain roles that the object plays. For example, the gameOver() and getWinner() methods are fundamental parts of the definition of a TwoPlayerGame. One cannot define a game without defining these methods. By contrast, methods such as play(), getGamePrompt(), and reportGameState() are important for playing the game but they do not contribute in the same way to the game's definition. Thus these methods are best put into an interface. Therefore, one important design guideline is:
    [Page 384]
    Effective Design: Abstract Methods
    Methods defined abstractly in a superclass should contribute in a fundamental way to the basic definition of that type of object, not merely to one of its roles or its functionality.
    8.6.6. The Revised OneRowNim Class
    Figure 8.21 provides a listing of the revised OneRowNim class, one that fits into the TwoPlayerGame class hierarchy. Our discussion in this section will focus on the features of the game that are new or revised.
    Figure 8.21. The revised OneRowNim class, Part I.
    (This item is displayed on page 385 in the print version)
    public class OneRowNim extends TwoPlayerGame implements CLUIPlayableGame {
    public static final int MAX_PICKUP = 3;
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    private int nSticks = MAX_STICKS;
    public OneRowNim() { } // Constructors
    public OneRowNim(int sticks) {
    nSticks = sticks;
    } // OneRowNim()
    public OneRowNim(int sticks, int starter) {
    nSticks = sticks;
    setPlayer(starter);
    } // OneRowNim()
    public boolean takeSticks(int num) {
    if (num < 1 || num > MAX_PICKUP || num > nSticks)
    return false; // Error
    else // Valid move
    { nSticks = nSticks - num;
    return true;
    } // else
    } // takeSticks()
    public int getSticks() {
    return nSticks;
    } // getSticks()
    public String getRules() {
    return "\n*** The Rules of One Row Nim ***\n" +
    "(1) A number of sticks between 7 and " + MAX_STICKS +
    " is chosen.\n" +
    "(2) Two players alternate making moves.\n" +
    "(3) A move consists of subtracting between 1 and\n\t" +
    MAX_PICKUP + " sticks from the current number of sticks.\n" +
    "(4) A player who cannot leave a positive\n\t" +
    " number of sticks for the other player loses.\n";
    } // getRules()
    public boolean gameOver() {   /*** From TwoPlayerGame */
    return (nSticks <= 0);
    } // gameOver()
    public String getWinner() {        /*** From TwoPlayerGame */
    if (gameOver()) //{
    return "" + getPlayer() + " Nice game.";
    return "The game is not over yet."; // Game is not over
    } // getWinner()
    The gameOver() and getWinner() methods, which are nowinherited from the TwoPlayerGame superclass, are virtually the same as in the previous version. One small change is that getWinner() now returns a String instead of an int. This makes the method more generally useful as a way of identifying the winner for all TwoPlayerGames.
    Similarly, the getGamePrompt() and reportGameState() methods merely encapsulate functionality that was present in the earlier version of the game. In our earlier version the prompts to the user were generated directly by the main program. By encapsulating this information in an inherited method, we make it more generally useful to all TwoPlayerGames.
    Inheritance and generality
    The major change to OneRowNim comes in the play() method, which controls the playing of OneRowNim (Fig. 8.22). Because this version of the game incorporates computer players, the play loop is a bit more complex than in earlier versions of the game. The basic idea is still the same: The method loops until the game is over. On each iteration of the loop, one or the other of the two players, PLAYER_ONE or PLAYER_TWO, takes a turn making a movethat is, deciding how many sticks to pick up. If the move is a legal move, then it becomes the other player's turn.
    Figure 8.22. The revised OneRowNim class, Part II.
    (This item is displayed on page 386 in the print version)
    /** From CLUIPlayableGame */
    public String getGamePrompt() {
    return "\nYou can pick up between 1 and " +
    Math.min(MAX_PICKUP,nSticks) + " : ";
    } // getGamePrompt()
    public String reportGameState() {
    if (!gameOver())
    return ("\nSticks left: " + getSticks() +
    " Who's turn: Player " + getPlayer());
    else
    return ("\nSticks left: " + getSticks() +
    " Game over! Winner is Player " + getWinner() +"\n");
    } // reportGameState()
    public void play(UserInterface ui) { // From CLUIPlayableGame interface
    int sticks = 0;
    ui.report(getRules());
    if (computer1 != null)
    ui.report("\nPlayer 1 is a " + computer1.toString());
    if (computer2 != null)
    ui.report("\nPlayer 2 is a " + computer2.toString());
    while(!gameOver()) {
    IPlayer computer = null; // Assume no computers
    ui.report(reportGameState());
    switch(getPlayer()) {
    case PLAYER_ONE: // Player 1's turn
    computer = computer1;
    break;
    case PLAYER_TWO: // Player 2's turn
    computer = computer2;
    break;
    } // cases
    if (computer != null) {                           // If computer's turn
    sticks = Integer.parseInt(computer.makeAMove(""));
    ui.report(computer.toString() + " takes " + sticks + " sticks.\n");
    } else {                                          // otherwise, user's turn
    ui.prompt(getGamePrompt());
    sticks =
    Integer.parseInt(ui.getUserInput()); // Get user's move
    if (takeSticks(sticks)) // If a legal move
    changePlayer();
    } // while
    ui.report(reportGameState()); // The game is now over
    } // play()
    } // OneRowNim class
    Let's look now at how the code decides whether it is a computer's turn to move or a human player's turn. Note that at the beginning of the while loop, it sets the computer variable to null. It then assigns computer a value of either computer1 or computer2, depending on whose turn it is. But recall that one or both of these variables may be null, depending on how many computers are playing the game. If there are no computers playing the game, then both variables will be null. If only one computer is playing, then computer1 will be null. This is determined during initialization of the game, when the addComputerPlayer() is called. (See above.)
    In the code following the switch statement, if computer is not null, then we call computer.makeAMove(). As we know, the makeAMove() method is part of the IPlayer interface. The makeAMove() method takes a String parameter that is meant to serve as a prompt, and returns a String that is meant to represent the IPlayer's move:
    public interface IPlayer {
    public String makeAMove(String prompt);
    [Page 385]
    In OneRowNim the "move" is an integer, representing the number of sticks the player picks. Therefore, in play() OneRowNim has to convert the String into an int, which represents the number of sticks the IPlayer picks up.
    On the other hand, if computer is null, this means that it is a human user's turn to play. In this case, play() calls ui.getUserInput(), employing the user interface to input a value from the keyboard. The user's input must also be converted from String to int. Once the value of sticks is set, either from the user or from the IPlayer, the play() method calls takeSticks(). If the move is legal, then it changes whose turn it is, and the loop repeats.
    [Page 386]
    There are a couple of important points about the design of the play() method. First, the play() method has to know what to do with the input it receives from the user or the IPlayer. This is game-dependent knowledge. The user is inputting the number of sticks to take in OneRowNim. For a tic-tac-toe game, the "move" might represent a square on the tic-tac-toe board. This suggests that play() is a method that should be implemented in OneRowNim, as it is here, because OneRowNim encapsulates the knowledge of how to play the One-Row Nim game.
    Encapsulation of game-dependent knowledge
    [Page                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

  • ".. is an abstract class.  It can't be instantiated"

    Does anyone have an idea of how I can get rid of the above error message? Here is a bit of my code:
    import java.io.*;
    import java.util.Vector;
    class Project3 {
    private BiTree company = new BiTree();
    public static void main(String[] args) throws IOException {
    Project3 run = new Project3();
    run.Command();
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    public interface comparable {
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    public void add() {
    Employee newOne = new Employee();
    System.out.println("Enter name");
    BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));;
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    BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));;
    String title = stdin.readLine();
    System.out.println("Enter payrate");
    BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));;
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    newOne.setTitle(title);
    newOne.setName(name);
    newOne.setPayrate(payrate);
    company.insert(newOne);
    }

    It is not possible to create instances of an abstract class.
    I hope this example helps,
    abstract class Vehicle
    public static void main(String arg[])
    Vehicle a;
    a = new Automobile(); // ok, since Automobile is a kind of Vehicle
    // The class Automobile, a special case of Vehicle
    class Automobile extends Vehicle

  • Abstract Class can't be instantiated

    Hi I'm getting the following error messages while compiling. Does any one have any idea how to get RID of it?
    ERROR MESSAGES:
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    public TableCellRenderer getTableCellRendererComponent(
    ^
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    Here is the code:
    EditableHeaderTableExample2.java
    import java.awt.*;
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    import javax.swing.JComponent;
    import javax.swing.JComboBox;
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    import javax.swing.*;
    import javax.swing.table.*;
    import javax.swing.border.*;
    import javax.swing.JTable;
    import javax.swing.plaf.metal.*;
    import javax.swing.JFrame;
    import javax.swing.table.TableColumn;
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    import javax.swing.DefaultCellEditor;
    import javax.swing.table.TableCellRenderer;
    import javax.swing.table.DefaultTableCellRenderer;
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    public static void main(String[] args) {
    EditableHeaderTableExample2 frame = new EditableHeaderTableExample2();
    frame.setSize(400,300);
         frame.setLocation(100,100);
         frame.setVisible(true);
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    for (int i=0;i<items.length;i++) {
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    This is not a suggestion, it's a requirement. When you say
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        Component getTableCellRendererComponent(JTable table, Object value,
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  • Abstract Method Error and XML Parsing

    I am using wl6sp1. I am parsing an XML file from within the
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    I'm assuming you have already put crimson.jar first in the classpath for the java
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    Regards,
    Mike Wooten
    "anyz" <[email protected]> wrote:
    >
    I am using wl6sp1. I am parsing an XML file from within the
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    3 it says:
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    I think somehow wl is still using jaxp1.0 which is built in
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    Whats wrong with the code...or what configuration i am missing???

  • "Abstract" method in a non-abstract class

    Hi all.
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    It's like I would like to declare some abstract methods in a non-abstract class...
    Any ideas?

    The superclass just models the information held by
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    The information is taken from the database, by
    accessing the proper table (one for each subclass).??
    What do you mean by "models the information"?
    You should use inheritance (of implementation) only when the class satisfies the following criteria:
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    They are designed as a binding to a db table.And how is the superclass designed to handle db transactions? My guess (based on your description) is that it isn't. That should tell you right away that the subclasses should not extend your superclass.

  • Problem compiling Abstract class

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    Remove the semi-colon.
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  • Want to Generate custom logs with Log4J within Java Embedding activity

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    You can try this.
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  • Implementing Comparable in an abstract class

    Hi all,
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  • Beginner CORBA idl struct said to be abstract class

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        string firstName;
        string lastName;
        string streetAddress;
        string city;
        string country;
        string phone;
        string eMail;
        string fax;
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        string getFirstName();
        void setLastName(in string last);
        string getLastName();
        void setStreetAddr(in string add);
        string getStreetAddr();
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        int index = 0;
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          allRecs = new Record[index];
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            r.setCountry(recs.getString(6));
            r.setEmail(recs.getString(7));
            r.setPhone(recs.getString(8));
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          catch (SQLException ex)
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      public Record ()
      } // ctor
      public Record (int _recordNumber,
    String _firstName, String _lastName,
    String _streetAddress, String _city,
    String _country, String _phone,
    String _eMail, String _fax)
        recordNumber = _recordNumber;
        firstName = _firstName;
        lastName = _lastName;
        streetAddress = _streetAddress;
        city = _city;
        country = _country;
        phone = _phone;
        eMail = _eMail;
        fax = _fax;
      } // ctor
    } // class Record What do I need to do to implement these methods declared in the .idl file?

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