general irksome headbanging problem!

[Mike Smike]

Hi buddies!

Right, I have a problem. I've made a game with 100 squares, and in each square are units. There can be any number of Cavalry and Infantry. I have an abstract class 'FightingUnit' from which Cavalry and Infactry extend. Infantry have a max strength of 1, whereas Cavalry can have 2.

The problem is this! When there is just one cavalry unit left on a square, the total strength is 2. But if that unit loses just 1 strength, he should be left with 1. The unit does infact lose 1 strength but so does every other cavalry unit on the board belonging to that player!!! Below is my code:

public ArrayList adjustFUs(ArrayList fUnits, int oldStrength, int newStrength)
    {
        if(newStrength <= 0)
        {
            return empty;
        }
        else
        {
            int strengthLost = oldStrength - newStrength;
            Iterator units = fUnits.iterator();                        
            while(units.hasNext() && strengthLost > 0)
            {
                System.out.println("in the while loop. Units hasnext");
                FightingUnit fU = (FightingUnit)units.next();
                String fUType = fU.getType();
                if(fUType.equals("Cavalry"))
                {
                    int anFUStrength = fU.getStrength();
                    int newFUStrength = anFUStrength - 1;
                    if(newFUStrength == 0)
                    {
                        units.remove();
                    }
                    else
                    { 
                        fU.setStrength(newFUStrength);
                    }
                }          
                else //fU is a FootSoldier
                {
                    units.remove();
                }
                strengthLost--;
            }
            return fUnits;
        }
    }  

The problem is the line

fU.setStrength(newFUStrength);

I think! It calls the method setStrength which is declared in the FightingUnit class. But it calls it for every Cavalry unit on the entire board, not just the one losing strength

How can I do it so that just the strength value of that one unit changes and not the entire army. The strength must be set correctly as the method used in the interface to display strenght relies on this.

Hope someone can help

Thanks guys

Mike

[Nigel Browne]

As I guess you have a 10*10 grid, you should be storing the position of each of your fighting units. Therefore I would expect a method along the lines of adjustFUHealthAt(int [][]position, int unitType, int adjustment).

HTH
[ November 24, 2004: Message edited by: Nigel Browne ]

[Mike Smike]

Hmmm not quite. The board is a single ArrayList and each item in the list contains an ArrayList of Fighting Units, which can be any number of either Cavalry or Infantry. The strenght for each square is calculated by iterating through the Fighting Unit arraylist, and adding up the strengths. Therefore, the strength of a wounded cavalry unit needs to be set lower than a health cavalry unit.

A calvary unit is constructed like this

public class Cavalry extends FightingUnit
{
    public Cavalry(Player p)
    {
        super(p, "Cavalry", 2, 2, 1);
        /*
         * Type = Cavalry
         * Strength = 2
         * Speed = 2                 
         * Range = 1
         */
    }
}
     

I need to somehow change the strength for individual units...

Any ideas??

[Simon Birch]

It sounds like you actually have 1 Cavalry object, and that object is being referenced from each square where the player has Cavalry.

What code do you use to create new Cavalry objects?

Sorry if I'm suggesting something you have already looked into.

[Nigel Browne]

I suggest that at each position on your board you create two queues one for cavalry and one for infantry. As damage is done to your queue of cavalry, for example they take 5 damage points, you would check the health of the cavalry unit at the front of your queue, if for example that unit has only one health point left, it is popped off the front of the queue (it dies) and then the health of the next unit on the queue is checked and so on until all the damage points are allocated and units are popped off the front of the queue or it's health is decreased. This will require a method which allows the player to assign which type of unit to apply damage to.
Also it allows for units to be added to the back of the queue but the last unit to take damage will always receive it first.

[Ernest Friedman-Hill]

Originally posted by Simon Birch:
It sounds like you actually have 1 Cavalry object, and that object is being referenced from each square where the player has Cavalry.

Or another possibility is that the "strength" member in FightingUnit is static.

[Mike Smike]

Yes I do have 1 Cavalry object that is referenced from each square. I create them using the following method for example

 public void setTroopsOne()
    {
        FootSoldier footFU1 = new FootSoldier(playerOne);
        Cavalry cavalryFU1 = new Cavalry(playerOne);
        ArrayList p1FootFUs = new ArrayList();
        ArrayList p1CavalryFUs = new ArrayList();
        p1FootFUs.add(footFU1);
        p1CavalryFUs.add(cavalryFU1);        
        SquareData p1Foot = new SquareData(p1FootFUs);
        SquareData p1Cavalry = new SquareData(p1CavalryFUs);
        for(int i = 0; i < 10; ++i)
        {
            gameBoard.set(i, p1Cavalry);
        }            
        for(int i = 10; i < 20; ++i)
        {
            gameBoard.set(i, p1Foot);
        }
    }  

That initialises them onto the board. The FightingUnit constructor is as follows :

public abstract class FightingUnit  
{
    // instance variables
    Player owner;
    String type;    
    protected int strength;
    int speed;
    int range;
        
    public FightingUnit(Player owns, String typ, int str, int sp, int rng)
    {
        owner = owns;
        type = typ;
        strength = str; 
        speed = sp;
        range = rng;
    }  

So if the strength variable is static, how can I change it for just one unit?

Thanks for all your help guys!

[Simon Birch]

Sorry about the delayed response, I suddenly remembered I had a home to go to!!

Anyway, object variables in Java contain references to objects. So two, or more, variables can point to the same object. Modifying the state of the object using one of the variables will be visible by accessing the object through the other variable.

SomeObject o1 = new SomeObject();
SomeObject o2 = o1;
o1.someProperty = 23;
System.out.println(o2.someProperty);

The above code will print out 23 (assuming the SomeObject class has been defined)

So, your code creates some new objects here

        FootSoldier footFU1 = new FootSoldier(playerOne);
        Cavalry cavalryFU1 = new Cavalry(playerOne);
        ArrayList p1FootFUs = new ArrayList();
        ArrayList p1CavalryFUs = new ArrayList();

The rest of the code uses those objects, and never creates any new ones, so you end up with lots of references to a single object. As soon as you change the strength through one reference, you can see the change through all the other references.

You need to create 1 Cavalry or FootSoldier object for each 'piece' on the board. Try this

 public void setTroopsOne()
    {
        for(int i = 0; i < 10; ++i)
        {
          FootSoldier footFU1 = new FootSoldier(playerOne);
          Cavalry cavalryFU1 = new Cavalry(playerOne);
          ArrayList p1FootFUs = new ArrayList(footFU1);
          ArrayList p1CavalryFUs = new ArrayList(cavalryFU1);
          SquareData p1Foot = new SquareData(p1FootFUs);
          SquareData p1Cavalry = new SquareData(p1CavalryFUs);
          gameBoard.set(i, p1Foot);
          gameBoard.set(i, p1Cavalry);
        }
    } 

Does that make sense?

[Mike Smike]

Yeah that makes loads of sense!! Thanks for spelling it out so clearly for me. I still seem to have fundamental misunderstandings with Java :roll:

I'll give it a go now.

Thanks again for speedy response and great advice



Mike