Creating an Object in java outside of the init

问题

so for the game I'm creating I have a few classes that extend GameDriver.

Up until this point, on all the other classes I've been able to extend GameDriver and then In GameDriver I can do:

ArrayList<Card>  library = new ArrayList<Card>();

Today I started on the GameAI class and I extended GameDriver, and when I put:

GameAI Enemy = new GameAI();

In the same spot I put the other line of code (Right below public class GameDriver)

I get:

java.lang.StackOverflowError
at java.util.WeakHashMap.expungeStaleEntries(Unknown Source)
at java.util.WeakHashMap.getTable(Unknown Source)
at java.util.WeakHashMap.get(Unknown Source)
at java.awt.Component.checkCoalescing(Unknown Source)
at java.awt.Component.<init>(Unknown Source)
at java.awt.Container.<init>(Unknown Source)
at java.awt.Panel.<init>(Unknown Source)
at java.awt.Panel.<init>(Unknown Source)
at java.applet.Applet.<init>(Unknown Source)
at GameDriver.<init>(GameDriver.java:14)
at GameAI.<init>(GameAI.java:8)
at GameDriver.<init>(GameDriver.java:40)
at GameAI.<init>(GameAI.java:8)

If I put it in the public void init() of my applet, then it doesn't give an error on run, but then I wouldn't be able to access it from my other methods, am I over looking something? All nighters normally don't help my brain...

This is what the GameAI looks like as of right now:

public class GameAI extends GameDriver {

    public int life;
    public int energy;

    public void drawPhase(){

    }

    public GameAI(){
        life = 20;
        energy = 2;
    }
}

And then some bits of the GameDriver:

public class GameDriver extends Applet implements MouseMotionListener,MouseListener {

Graphics g; 
Image offscreen;
Dimension dim; 

int playerLife = 20;
int playerEnergy = 8;

int xMouse; 
int yMouse;
int lineThickness = 4;
int handSize = 6;
int currentHover;
boolean slotHover;
int currentSelected;
boolean slotClicked;
int currentHoverBoard;
boolean slotHoverBoard;
boolean slotClickedBoard;
int currentSelectedBoard;

boolean canPlace;
ArrayList<Card>  library = new ArrayList<Card>();
ArrayList<Card>  hand = new ArrayList<Card>();
ArrayList<Card>  playerBoard = new ArrayList<Card>();
GameAI Enemy;
int[] handBoxX = new int[handSize];
int[] handBoxY = new int[handSize];
int[] handBoxW = new int[handSize];
int[] handBoxH = new int[handSize];

int[] playerBoardX = new int[8];
int[] playerBoardY = new int[8];
int[] playerBoardW = new int[8];
int[] playerBoardH = new int[8];



public void init(){
    this.setSize(640, 480);
    dim = this.getSize();
    addMouseMotionListener(this);
    addMouseListener(this);
    createLibrary();
    drawFirstHand();
    printHand();


    GameAI Enemy = new GameAI();
    checkEnemy();



    offscreen = createImage(this.getSize().width,this.getSize().height);
    g = offscreen.getGraphics(); 
}

public void checkEnemy(){
    System.out.println(Enemy.energy);
}

... Alot more methods and stuff below, but nothing to do with the GameAI enemy

回答1:

You're creating a GameAI object inside of GameDriver, the class it extends. This will cause recursion to continue until you run out of memory.

Solution: don't do this. Your GameAI class should not extend GameDriver as that's the wrong way to share information and it simply won't work even if you didn't have this recursion nightmare. Instead give GameAI a GameDriver field and pass the GameDriver instance into GameAI through its constructor.

i.e.,

class GameAI {
   private GameDriver gameDriver;

   public GameAI(GameDriver gameDriver) {
      this.gameDriver = gameDriver;
   }

   //.... more code
}

Edit 2
If you want one GameAI object, you'd do

GameAI gameAi = new GameAI(this);

If you want an array or List of them, you'd do this in a loop.

来源：https://stackoverflow.com/questions/12027435/creating-an-object-in-java-outside-of-the-init

标签

java

oop

class