Why does the stack size of an item in the inventory not change when used?

Question

Problem :

I have a problem with my program where, when I want to decrease the stack size of an item in the inventory by 1, it doesn't change, when a certain button is pressed (eg 'space').

Expected Result :

What should happen is when 'space' is pressed, the stack size of the current item should change.

Code :

UseItem() :

if (coreEngine.getKeyManager().space) {
        useEnergy(Creature.DEFAULT_ENERGY_COST);
        inventory.useItem(inventory.getCurrentItem(), inventory.getCurrentSelection().getSlotID());
        CEMessage.printMessage("[stackSize]: " + inventory.getCurrentSelection().getCurrentStack());
        //stackSize of currentItem doesn't change when used
}

inventory.useItem() :

public void useItem(Item item, int slotIndex) {
    if (slotsList.get(slotIndex).getItem() == item) {
        slotsList.get(slotIndex).useItem(item); 
    }
}

slot.useItem() :

public void useItem(Item item) {
    currentStack = item.getStackSize();
    currentStack--;
}

getCurrentItem() :

public Item getCurrentItem() {
    return slotsList.get(currentSelection).getItem();
}

getCurrentSelection() :

public Slot getCurrentSelection() {
    return slotsList.get(currentSelection);
}

Answer 1

It is hard to answer without a little bit more of tests. in the following code :

public void useItem(Item item, int slotIndex) {
if (slotsList.get(slotIndex).getItem() == item) {
    System.out.println("reach here ?");
    slotsList.get(slotIndex).useItem(item); 
}}

If it does not print something on the console, it is surely because of slotsList.get(slotIndex).getItem() == item and it would mean that you are comparing two object of the same type but with different references (not the same instance of the class).

---

EDIT : Answer

Here is the right answer then. There are two steps. First, you go to your Item class and you create a methode like this :

public boolean equals(Item itemToCompare)

. In that method, what you have to do is to compare the value of the common attribute of all the Item objects that differenciate them. For example, if one item has a name, you have to do :

public boolean equals(Item itemToCompare) {
 if (this.name.equals(itemToCompare.name))
    return true;
 else
    return false;
  }

Answer 2

I believe the issue is here.

public void useItem(Item item) {
    currentStack = item.getStackSize();
    currentStack--;
}

Try this

public void useItem(Item item) {
    currentStack = item.getStackSize();
    item.setStackSize(currentStack - 1);
}

Integers are "immutable" which means once they are made they can't be altered. When you do i-- it's making a new Object or int value, not modifying the one that was there. So the stackSize value in item is still pointing at the old value.

---

Quick example of immutable versus mutable Objects

class MutableFoo {

    private Object bar;

    public void setBar(Object bar) {
        this.bar = bar;
    }

    public Object getBar() {
        return bar;
    }
}

In the above you can modify MutableFoo by using setBar .

class ImmutableFoo {

    private Object bar;

    ImmutableFoo(Object bar) {
        this.bar = bar;
    }

    public Object getBar() {
        return bar;
    }
}

In here however there is no way to modify ImmutableFoo , we can only use the constructor to set bar 's value so if we want to "modify" an ImmutableFoo we need to make a new one.

It's the difference between

Object bar = ...
MutableFoo mFoo = new MutableFoo();
mFoo.setBar(bar);
Object newBar = ...
mFoo.setBar(newBar);

and

Object bar = ...
ImmutableFoo iFoo = new ImmutableFoo(bar);
Object newBar = ...
iFoo = new ImmutableFoo(newBar); // Have to make a new ImmutableFoo.