Question

I have a need to store a list of dynamically created objects in a way where they can all be retrieved and their methods called on demand.

As far as I can see for the list and creation, a HashMap fits my needs but i’m a bit puzzled on recalling the objects and calling their methods using the HashMap.

Just as a reference, let me give you a little code:

Here is the HashMap:

Map<String, Object> unitMap = new HashMap<String, Object>();

// here is how I put an object in the Map notice i'm passing coordinates to the constructor:
unitMap.put("1", new Worker(240, 240));
unitMap.put("2", new Worker(240, 240));

Now I need to create a method that retrieves every object in the hashmap and call a method from each object. is this possible or can the created objects only be referenced directly. If so, is there another way to call a method of all existing instances of a class dynamically (in other words, on user input)?

Answer 1

Sure. You can do this:

for (Object thing : unitMap.values()) {
    // use "thing" here
}

If you need the keys too, you can either get just the keys:

for (String key : unitMap.keySet()) {
    // use "key" here
}

or both the keys and values together:

for (Map.Entry<String, Object> entry : unitMap.entrySet()) {
    // use "entry.getKey()" and "entry.getValue()"
}

In all the above cases, each entry in the map is traversed one by one. So at the end of the loop, you’ll have processed all the entries in the map.