I am currently working on my exam-project for uni. The task is to create the boardgame ludo. After writing some code and doing some testing, I ran into a StackOverflowError.
So here is the structure (5 classes are essential):
Main.class GUI.class Game.class Player.class Piece.class
Main creates a new object of type GUI called mainGUI. This creates the visuals for the game, including a small settings area with a start button.
On the press of the Start button, a new object of the type Game is created which then creates 4 new Objects of the type Player (4 players obviously).
When creating an object of type Player, this type gets the argument 'nmbr' which just states the Number of the Player (Player1, Player2 and so on).
Each Player has 4 pieces to move around on the board, so each of those 4 Players create another 4 objects of type Piece.
Now when pressing the Start button, what should happen is, that the pieces are displayed on the board. But that doesn't happen. Instead I get an errormessage stating, that there is a StackOverflowError on the call of the first Player object.
So I tried to read into the behaviour of Object creation in java and StackOverflow and stuff like that. But the only conclusion I can get right here, is that I've created too many objects inside one another.
public class Main {
public static void main(String[] args){
Main start = new Main();
start.activate();
}
static GUI mainGui;
public Main() {
mainGui = new GUI();
}
Inside the GUI there is the JButton 'submit'
This button is supposed to start the game by creating the an object of the type Game.
submit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object btn = e.getSource();
boolean ACTIVE = ((JButton) btn).isEnabled();
if (ACTIVE) {
submit.setVisible(false);
cancel.setVisible(true);
Game spiel = new Game();
spiel.begin();
}
}
});
public class Game {
public Game() {
}
Player player1 = new Player(1); //this is where the Error occurs
Player player2 = new Player(2);
Player player3 = new Player(3);
Player player4 = new Player(4);
}
etc.
public class Player extends Game {
private String name;
private Color color;
private boolean artiPlayer;
private int playerNmbr, start, end;
private int[] startArea, endArea;
Piece piece1, piece2, piece3, piece4;
public Player(int nmbr){
if (nmbr == 1) {
System.out.println("1.1");
piece1 = new Piece(500,175, Color.BLUE, Main.mainGui);
piece2 = new Piece(550, 175, Color.BLUE, Main.mainGui);
piece3 = new Piece(500,125, Color.BLUE, Main.mainGui);
piece4 = new Piece(550, 125, Color.BLUE, Main.mainGui);
start = 0;
end = 64;
}
}
Type Piece => Piece(xPos, yPos, Color, GUI)
//and so on
Here is the exact error message:
Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
at spielPackage.Player.<init>(Player.java:18)
at spielPackage.Game.<init>(Game.java:9)
Sorry if the code is a bit unclean. I am fairly new to java and this is still a work in progress.
At this point I am lost as to why Java throws a StackOverflowError
Your Player should not extend Game since a Player is not a Game.
Right now you create a game which creates four players with every one of them being a different "Game" and creating four more players which are games and create four new players each......
Related
For a project I am involved in, I have the task of writing some code to be able to save and load the current gamestate. Now, being that I am using java, I already know Serialization is probably the best way to go about this. Now, the gamestate that I have to save involves one main class witha singleton pattern shown here:
public class Game implements java.io.Serializable
{
private static ArrayList<Room> world;
private static Game game = nul
private Game(){}
public static Game getGame()
{
if (game != null)
{
game = new Game();
}
return game;
}
A little bit further down in the code are a bunch of objects that are used to help the game run.
Position heroPos = new Position(HERO_ROOM_INDEX,
HERO_POS_X, HERO_POS_Y);
Rectangle heroHitbox = new Rectangle(
new Position(HERO_ROOM_INDEX,
HERO_HITBOX_X_OFFSET, HERO_HITBOX_Y_OFFSET),
HERO_HITBOX_WIDTH,
HERO_HITBOX_HEIGHT);
Entity hero = new Player(heroPos, heroHitbox, HERO_SYMBOL);
Position leverPos = new Position(getPlayerRoomIndex(), LEVER_POS_X,
LEVER_POS_Y);
(The actual code is pretty long and would be hard to read, but it follows mostly the same format)
Where Entity, Rectangle, Position are all separate classes in different packages than Game. So, if I were to try and serialize this Game object, how would I go about it? Would I have to use ObjectOutputStream to write every single object that Game creates into a file? Or do I just have to make sure that all of these classes that Game uses implement the Serializable interface, and then just serialize the Game object?
So I've been learning how to use the jme3 engine and SDK. I started toying around with working outside of the main application file that extends SimpleApplication to further objet-orient my application.
My question is this.. How do I correctly initialize the physics object? As in.. You create a Player class that has a BulletAppState object named phyiscs, but is not assigned a value AT FIRST! It is assigned within the constructor.
class Player {
BulletAppState physics;
public Player(BulletAppState physicsState) {
this.physics = physicsState; // State should now be initialized when
// this constructor is is called
}
}
Then, in the main class file
class Main extends SimpleApplcation {
Player player;
BulletAppState physics;
public static void main(String[] args) {
Main app = new Main();
app.start();
}
#Override
public void simpleInitApp() {
physics = new BulletAppState();
physics.setThreadingType(BulletAppState.ThreadingType.PARALLEL);
stateManager.attach(physics);
player = new Player();
}
}
I do not get the desired result that I expect.
The output results are:
Main class physics state enabled? True
Player class physics state enabled? False
Just pass the physics in your Player() constructor to initialize BulletAppState like this.
player = new Player(physics);
Big hint: stateManager.attach() adds the thing to a Queue!
The only appStates that are initialized during the call to simpleInitApp are those passed into the constructor at new Main(appStates...)
I've got this working well in my object-oriented game project:
Main app = new Main( new StatsAppState(), new FlyCamAppState(), new DebugKeysAppState(), physics );
And it passes nicely to all objects in the simpleInitApp() call.
I am making a game, I have got several different classes as I dont like to put everything in one. I have a GameView class and a players class. The problem is that I am calling a method in players class from GameView. But its giving me an null pointer error. Below is my code:
GameVie class:
Panel p2 = new Panel();
p2.setLayout(new BorderLayout());
JLabel player1Lbl = new JLabel("Player 1");
p2.add(player1Lbl, BorderLayout.WEST);
player.enterNameP1(); //Having an error here.
player1Lbl.setText(player.enterNameP1());
Players Class:
public class Players
{
//storing the player 1 name
private String p1name;
//storing the player 2 name
private String p2name;
/**
* Constructor for objects of class Players
*/
public Players()
{
this.p1name = p1name;
this.p2name = p2name;
}
/**
*Enter the player 1 name in a dialog box
*/
public String enterNameP1() //It was public void before but it wasnt accepting a void method in the gameView so I changed it to String
{
this.p1name = JOptionPane.showInputDialog("Please enter player 1 name","Specify name");
return p1name;
}
you should initialized player first..... ?
Players player = new Players();
Your player isn't initialised at the moment you call:
player.enterNameP1(); //Having an error here.
To solve this, you have to make sure that the reference player actually points to a real instance of Player. This should be done by adding at a logic place in your code this:
player = new Players();
That is the reason why you got a NullPointerException. When you call a method from a specific object, the object must be initialised (which means that the pointer player points to an actual instance of the class Players).
You did not instantiated player
So it is null causing a NPE
So I have this code:
package com.erikbalen.game.rpg;
import com.erikbalen.platform.*;
import javax.swing.JFrame;
public class World extends Engine {
public static void main(String[] args) {
Gui display = new Gui(/*takes a Player argument so i can get certain variables*/);
display.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
display.setSize(300,220);
display.setVisible(true);
Player player1 = new Dps("ebalen", display);
Player player2 = new Healer("frankypanky", display);
}
}
package com.erikbalen.game.rpg;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class Gui extends JFrame implements ActionListener {
/**
*
*/
private static final long serialVersionUID = -384241835772507459L;
private JLabel playerInfo;
private JTextField textField;
private final static String newline = "\n";
private JTextArea feed;
private JScrollPane scrollPane;
private Player player;
public Gui(Player currentPlayer) {
super("Erik's RPG");
this.player = currentPlayer;
setLayout(new FlowLayout());
playerInfo = new JLabel("<html>Health = " + currentPlayer.getHealth() + " | " + "Mana = " + currentPlayer.getMana() + "</html>");
playerInfo.setBorder(BorderFactory.createTitledBorder(currentPlayer.getName()));
textField = new JTextField(20);
textField.addActionListener(this);
feed = new JTextArea(5, 20);
scrollPane = new JScrollPane(feed);
feed.setEditable(false);
add(playerInfo);
add(feed);
add(textField);
add(scrollPane);
}
public void actionPerformed(ActionEvent textBox) {
String text = textField.getText();
this.player.chat(text);
}
public void printText(String text) {
feed.append(text + "\n");
feed.setCaretPosition(feed.getDocument().getLength());
}
}
My problem is that class Gui takes a Player as an argument and Player takes Gui as an argument. How do I let both objects take each other as arguments? Feel free to tell me if my code is inefficient.
Well, ideally you should try to break the circular dependency, but otherwise, you could:
Create the GUI, create the players by passing in the GUI, then add the players to the GUI
Create the players, create the GUI by passing in the players, then set the GUI for the players
Create the GUI within the player constructor:
Player(String name)
{
GUI gui = new GUi(this);
...
}
All of these are non-ideal:
You may well want your classes to be immutable, which makes the first two options nasty
Publishing the this reference before your constructor has finished executing has various issues, both in terms of thread safety and the memory model, as well as potentially allowing the GUI constructor to call back to the Player object before it's fully initialized.
This goes back to "try to break the dependency" - but if that's really impossible, I would probably favour the first option, without knowing anything else. It makes sense to be able to add players to a game - it makes less sense to set the GUI for a player after the fact, IMO.
Your stuck in what we call a circular dependency. This is almost everytime the result of a bad design.
There are still solutions, but there are not really pretty. For an elegant way, you should rethink your design.
Does the GUI really need the player ? Maybe you could create a method to set the player later on. If it's not possible, you could also create a setter in the player. You won't be able to set both at construction time.
Try giving the Gui class methods for updating what is displayed to the user/users. Make the directing code (main() for example) responsible for updating the Gui with the right information as events happen.
Neither Gui nor Player should have to take each other as constructor arguments - Gui should only be responsible for displaying information it is told to, and Player should only be a logical representation of a game piece. Event-driven functionality should be reserved for the directing code.
I'm trying to create a blackjack program for my final project in Java. I'm still very new to Java and OOD so I apologize if my problem seems very trivial to you :(
How my program works: I have three classes so far.
main.java
This class builds my frame and runs all the other methods.
cards.java
This class creates an array that holds the card values and location to picture. I have a for loop in there that auto-populates it.
hits.java
This class is meant to "randomly" generate a number that will represent the chosen card. The way this works is by taking the randomly created int and pointing it to a matching index location on the array.
I assign the value to string objects that I then try to add to a jlabel and then add that jlabel to my main frame. The code is as follows:
hits.java
// Import necessary classes.
import java.util.Random;
public class hits {
// Create random object.
Random rand = new Random();
// Declare variables.
int card;
String cardVal, cardPic;
// Instantiate the needed classes.
main s = new main();
cards t = new cards();
// Constructor for the class.
public hits() {
// Randomly generate a number (0 - 9).
card = rand.nextInt(10);
// Populate the array.
t.runCards();
// Assign the cards according to the num. generated.
cardVal = t.deck[card][0];
cardPic = t.deck[card][1];
}
// Run Method
public void runHits() {
// Add the card chosen to the GUI.
s.a.setText("hello");
s.dealerCards.add(s.a);
}
}
I have "hello" as the text for the label because I wanted to see if perhaps my array was not populating, but even that doesn't work. If it helps here is my main.java as well (constructor and main method):
// Constructor for the main class.
public main() {
// Setup the MAIN container.
f1.getContentPane().setLayout(new GridLayout(0, 1));
f1.setSize(200, 200);
f1.add(dealerName);
f1.add(dealerCards);
f1.add(userCards);
f1.add(userName);
// Setup the inner panels.
dealerCards.setLayout(new GridLayout(1, 2));
dealerCards.add(b);
userCards.setLayout(new GridLayout(1, 6));
userCards.add(c);
userCards.add(d);
}
// Build the frame.
public void GUILaunch() {
// Display Frame
f1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f1.setVisible(true);
}
// Main method.
public static void main(String args[]) {
// Distribute the dealer's/player's starting hands.
hits deal = new hits();
deal.runHits();
// Launch the GUI
main gui = new main();
gui.GUILaunch();
}
Hopefully I have provided enough information to help you understand what's going on here. So to sum it all up: how can i add my jlabel(from another class) holding the randomly selected card to my main frame
Thanks in advance.
The deal.runHits() adds a label to the Main object that deal owns rather than the gui object.
I would suggest the following :
Make your main class have an instance of hits and hits have an instance of the cards object...
so you get something like this
public class main {
private hits hits_instance
//constructor
main(){ hits_instance = new hits(); }
//this method will add your cards
public void addCards(){
// frame = whatever frame you are using
frame.add(hits_instance.getCards());
}
}
public class hits {
private cards cards_instance;
hits(){ cards_instance= new cards();}
public JLabel getCards() {return cards_instance.getCard(randomNumber);}
}