Is it good practice to often use instanceof?

Question

The scenario. I\'m writting game-related code. In that game a Player(its also a class) has a list of Item. There are other types of items that inhe

Answer 1

Let's say I am writing some inventory code:

public void showInventory(List items) {
    for (Item item : items) {
        if (item instanceof ContainerItem) {
            // container display logic here
        }
        else if (item instanceof WeaponItem) {
            // weapon display logic here
        }
        // etc etc
    }
}

That will compile and work just fine. But it misses out on a key idea of object oriented design: You can define parent classes to do general useful things, and have child classes fill in specific, important details.

Alternate approach to above:

abstract class Item {
    // insert methods that act exactly the same for all items here

    // now define one that subclasses must fill in themselves
    public abstract void show()
}
class ContainerItem extends Item {
    @Override public void show() {
        // container display logic here instead
    }
}
class WeaponItem extends Item {
    @Override public void show() {
        // weapon display logic here instead
    }
}

Now we have one place to look, the show() method, in all our child classes for inventory display logic. How do we access it? Easy!

public void showInventory(List items) {
    for (Item item : items) {
        item.show();
    }
}

We are keeping all the item-specific logic inside specific Item subclasses. This makes your codebase easier to maintain and extend. It reduces the cognitive strain of the long for-each loop in the first code sample. And it readies show() to be reusable in places you haven't even designed yet.