Marking a Location

Programming Questions

dlillard5

in Programming Questions • 1 year ago

What is the best way to mark a location as occupied? in the past I've used get(), but this is harder to maintain if I have different classes, and seems like a shortcut. Is it better to mark each location with a class or an array? If i use a class then you end up with (width*height) amount of classes which isn't good for performance. I hope that's clear enough. Any help is appreciated

Replies(7)

jbum

Re: Marking a Location

1 year ago

I assume you are asking how to keep track of a small number of cells that occupy a large two dimensional grid.

Assuming this is correct, you could use either an ArrayList or a HashMap, both of which only store objects for the number of occupied cells, versus every possible cell address.

The ArrayList is better if you will often iterate through the objects one by one. The HashMap is better if you want to frequently check if a particular cell is occupied - you can look up the cell by it's address (key).

dlillard5

Re: Marking a Location

1 year ago

Late response here...

Yes, I am trying to keep track of a small number of cells in a large 2d grid.

If I use a HashMap, I need to give it a key and a value. I want the key to be it's location, but I only can use one variable for the key (right?).

Do I need to give every location a 1d number?

PhiLho

Re: Marking a Location

1 year ago

You can put the location in a PVector, and use it as key.

dlillard5

Re: Marking a Location

1 year ago

HashMaps are just bewildering to me...

The following code won't run. I think all the syntax is correct (except for maybe line 10). What do I need to change?

HashMap hm=new HashMap();
void setup(){
size(500,500);
background(0);
}
void mouseReleased(){
hm.put(new PVector(mouseX,mouseY),1);
}
Iterator i = hm.entrySet().iterator();
while(i.hasNext()) {
Map.Entry me = (Map.Entry)i.next();
print(me.getKey() + "is occupied");
}

PhiLho

Re: Marking a Location

1 year ago

Well, your code just won't compile... You cannot put code in the wild (at the global level) when you define a function.
Here it a working version.

HashMap<PVector, Integer> hm = new HashMap<PVector, Integer>();
void setup() {
size(500, 500);
background(0);
}
void draw() {}
void mouseReleased() {
hm.put(new PVector(mouseX, mouseY), 1);
}
void keyPressed()
{
println("\n---\n");
Iterator i = hm.entrySet().iterator();
while (i.hasNext()) {
Map.Entry me = (Map.Entry) i.next();
println(me.getKey() + " is occupied");
}
}

The typing of the hash map isn't necessary here, but can be useful in other code.

dlillard5

Re: Marking a Location

1 year ago

Perfect thanks! That's a cool trick with the \n also... What do you mean the typing of the hash map isn't necessary?

PhiLho

Re: Marking a Location

1 year ago

I added <PVector, Integer> because it is good practice, but in the code above, it isn't really used.

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