Peebl Peebl - 2 months ago 10
Java Question

Easy way to add 3 different types of Objects to one ArrayList with one method?

This is a copy from an assignment I've done, so apologizes for some of the Norwegian commenting.

My question is:

I have an items ArrayList which holds Objects from the classes Item, Swords, Potions. (Potions & Swords are subclasses of Items). And I have 3 different methods to add these Objects to the ArrayList.

My question is Simple actually. Is there a (simple, I'm new and learning still) way for me to add all Items and Subclasses of Item to the ArrayList without having 3 different methods which look all alike. (addItem, addSword, addPotion), all close to the bottom of the code.

I'd want something like this ( not thought through, just wrote something)

public void addItem(String typeofItem){
item = new typeofItem;
items.add(item);
}


There is alot more to the code, but i feel like this is whats relevant.

public class Player
{
// Fields -------
private String name;
private String type;
private int health;
private ArrayList<Item> items = new ArrayList<>();
private Item item;
private Swords sword;
private Potions potion;
private Checker valid;
private int maxCarry;
private int gold;
private int currentWeight;
// ----------------

/**
* Klassens konstruktør. Players health vil alltid settes til 100.
*
* @param name Player navn
* @param type Player type
* @param goldValue Players starting gold
* @param setMaxWeight Players max carry weight
*/
public Player (String name, String type, int goldValue, int setMaxWeight) {
valid = new Checker(); // Creates a checker object to do String and integer checks

this.name = valid.checkString(name); // Setter player name, etter å ha sjekka at den ikke er tom
this.type = checkType(type); // Setter type, etter å ha processet den
health = 100; // Health skal alltid starte som 100
maxCarry = valid.checkInt(setMaxWeight); // Sets max carry weight
currentWeight = 0; // Start vekten til player
gold = valid.checkInt(goldValue); // setter goldbeholding etter å ha sjekka at den ikke er negativ
}

/**
* En metode for å selge ett Item objekt, reduserer gold og øker weight ved kjøp.
*
* @param item Item object to sell
*/
private void buyItem(Item item)
{
// Temporary values given from items methods getweight and getvalue to be used in a mutation
int tempWeight;
int tempValue;
tempWeight = item.getWeight();
tempValue = item.getValue();
// Checks if the item meets te conditions to be bought (enough gold, and can be carried)
if (checkConditions(tempValue, tempWeight)) {
// Adds the item to ArrayList if conditions met and updates gold and weight
items.add(item);
currentWeight += tempWeight;
gold -= tempValue;
}
}

/**
* Method to calculate if given value and weight is accepted to perform a purchase (total gold > 0 && total weight < maxWeight)
*
* @param value Gold value of item
* @param weight Weight of item
* @return boolean Returns true if conditions met
*/
private boolean checkConditions(int value, int weight)
{
if (!(gold >= value))
{
System.out.println("You don't have enough gold!");
return false;
} else {
if (!(weight + currentWeight <= maxCarry)){
System.out.println("You'll be too heavy carry this item!");
return false;
} else {
// All conditions met
return true;
}
}
}

/**
* Adds an item to player inventory (uses method buyItem to process the item as a purchase)
*
* @param itemName String to name item
* @param itemDesc String to describe item
* @param itemValue int to declare items value
* @param itemWeight int to declare items Weight
* @param itemAction String to give item an action
*/
public void addItem(String itemName, String itemDesc, int itemValue, int itemWeight, String itemAction)
{
// A Player generated item, which needs all parameters to specify it
item = new Item(itemName, itemDesc, itemValue, itemWeight, itemAction);
buyItem(item);
}

/**
* Randomly generates a Sword object and adds it to players inventory (uses buyItem to process)
* @see Swords#Swords
*/
public void addSword()
{
sword = new Swords();
buyItem(sword);
}

/**
* Randomly generates a Potion object and adds it to players inventory (uses buyItem to process)
* @see Potions#Potions
*/
public void addPotion()
{
potion = new Potions();
buyItem(potion);
}

Answer

You can create something called a Factory class. A factory class's responsibility is to generate instances of a type of item for you.

https://www.tutorialspoint.com/design_pattern/factory_pattern.htm

Essentially you wrap the method you talk about in a class and return a new instance of that object.

public class ItemFactory{

    public static Item addItem(String typeofItem){
        switch(typeofItem){
             case "Sword":
                return new Sword();
             case "Potion":
                return new Potion();
             ...
            default:
               //put any code here that is like the "else" of an if-else block
              return null;
        }
    }

}

Then when you need to add a new item of a specific type:

buyItem(ItemFactory.addItem("Sword"));