Hi guys,

From what I've searched up on google people are creating libraries to find differences between objects, I just want to be able to identify objects. Or rather find out if an object has an id.

The reason being, I'm trying to store an object inside of an array declared as an integer, so far I'm getting an error that's telling me the objects don't have IDs. which leads me to the question, how do I differentiate between objects ? one of the solutions I've looked at is by storing a value inside of a variable and basically creating your own ID for each object. Which kind of makes sense. But coming from GML each instance(java object) of an object(java class) has an id which is used for reference.

Why are you trying to store an object inside an array of integers? If you want to store an object into an array, the array needs to be declared with the same type as the object (or a supertype/interface of).

Also, what is the exact error message? If you are trying to store an object in an int array you should get an error saying that cannot assign object type to int or something similar, not that the object doesn't have an ID.

EDIT: also, related to the topic, you might find interesting to read about identity and equality in Java.

From what I've searched up on google people are creating libraries to find differences between objects, I just want to be able to identify objects. Or rather find out if an object has an id.

An object has a memory start address which is unique for each object. That is being used for identity checking (ie ==). The default implementation of "equals" also uses that (except for some standard objects like integers, reals, and strings, and such). By overriding "equals" you can have your own equality notion between objects. (However, given the kind of questions you ask, this is currently a little too far for now, so something to keep in mind for later.)

Edit: Sorry, I was talking total nonsense about equals: primitive types (int, double/float, and boolean) have no equals, and use == as equals. class-types (ie everything else than primitive types) have both == and equals, which may or may not check the same thing.

Here's my current code

package myPackage;


public class Server {
public static void main(String[] args) {


int Arr_Players_DB[] = new int [5]; //array object initialization


for (int i = 0; i < Arr_Players_DB.length ; i ++)
{
Arr_Players_DB[i] = -1; //Initialize array
}




for (int i = 0; i < Arr_Players_DB.length; i ++) // //populate array
{
Players_DB player = new Players_DB();
if (Arr_Players_DB[i] == -1)
{


Arr_Players_DB[i] = player;
}}}}

Why are you trying to store an object inside an array of integers? If you want to store an object into an array, the array needs to be declared with the same type as the object (or a supertype/interface of).

Also, what is the exact error message? If you are trying to store an object in an int array you should get an error saying that cannot assign object type to int or something similar, not that the object doesn't have an ID.

EDIT: also, related to the topic, you might find interesting to read about identity and equality in Java.

Error message is "Type mismatch: cannot convert from Players_DB to int"

Because I want a list, each list ID must be a reference to each object, each object holds variables which will equal to properties that I've assigned for each object. These will be for "Players" in the game in a server side application. So it makes sense that I should try and reference each object in an array.

The reason I've moved from using a 2D array for this is because Multidimensional Arrays in java require that each dimension be the same data type, which is a problem when I want to store "username String" and "password Integer"(for example).

I had a look at Identity and equality, all it's showing me is that objects can be referenced by creating a new object type and storing another object in that. Referencing yes..

So the idea then is when I create a new array

int Arr_Players_DB[] = new int [5]; //array object initialization

That the data type be that of an object, but that would work would it ?

You are posting a lot of threads, most of them on the same topic. Maybe it's time to slow down a little and work with tutorials and/or reading, instead of posting 6 threads in a single day?

They're all regarding java, and can be boiled down to reveal many similarities, how ever they are not the same. If you are not going to contribute to the topic then don't post. You are trying to be helpful, how ever let me help you understand that I am browsing the web while creating threads because it's things I've found on the web that don't make sense, specifically mentioned above regarding multidimensional arrays requiring the same data type which is when someone in that thread (not my thread) recommended referencing objects in arrays instead. So I'm not being lazy, or trying to make your day a little more difficult by scrolling by an additional 400 pixels to find a post worthy of your assistance. I'm trying to learn Java. So far this works for me.

From what I've searched up on google people are creating libraries to find differences between objects, I just want to be able to identify objects. Or rather find out if an object has an id.

An object has a memory start address which is unique for each object. That is being used for identity checking (ie ==). The default implementation of "equals" also uses that (except for some standard objects like integers, reals, and strings, and such). By overriding "equals" you can have your own equality notion between objects. (However, given the kind of questions you ask, this is currently a little too far for now, so something to keep in mind for later.)

Edit: Sorry, I was talking total nonsense about equals: primitive types (int, double/float, and boolean) have no equals, and use == as equals. class-types (ie everything else than primitive types) have both == and equals, which may or may not check the same thing.

This is similar to the link provided by Avalandor, there's an image which shows that each object holds a space within memory. What's new is that you're saying they have unique start addresses, I don't think It's suppose to get that complicated to find these addresses just to make a list of objects that can be referenced.

int Arr_Players_DB[] = new int [5]; //array object initialization

So, what you are doing here is create an array that holds Integer values,
you then go on to try an assign a non-integer value to it.

Players_DB Arr_Players_DB[] = new Players_DB [5]; //array object initialization

Is how it should be written to create an array that holds the class you are trying to put into it.


So far though, you seem to be jumping into things pretty randomly (having read and posted some replies in your other topics) They are all fairly starter topics but seemingly jumping around a bit.

I would suggest if you want to learn java pick up something like https://www.amazon.co.uk/Beginning-Java-Programming-Oriented-Approach/dp/1118739493 this book, as it would provide a much more structured approach to learning the language / programming in general.

Leaving out the many glaring holes and problems in the code that wont work by changing the array :D but yeah.. the code above really was just terribly written

Yes the problem is that I don't understand the syntax for the 'new' keyword which is what I'm currently looking up.

What is happening in the code you've provided ? Is it allocating 5(6) slots within the Arr_Players_DB[] Array, creating a new Players_DB object then adding it to the array ?

I see you're not initializing the array size before hand.

There are two ways to approach learning, There is the learn everything about something and then there's learning only what is relevant to the applications it's needed for. The one makes you more capable with a larger area of understanding, while takes longer and you may learn things that you'll never use, how ever may learn things that you may use, it's a gamble. The other is setting a goal, and over coming barriers on the way to that goal.

The way I would suggest my approach to someone over their approach is by establishing pros and cons with both manners, the reason I say suggest is because it's not always the case that you understand the other persons method. I'm going to stick with learning what is relevant, yes I am all over the place at the moment, but eventually the gap will be closed the more sense I can make of these relevant points.

Thank you for the information so far, there's something new at every avenue, right now I'm stumped with how I want to reference objects in an array, in your code it looks like you're creating the objects at the same time as assigning them to an array. which looks like the way I want to go about it.

So what the code provided does is it create a new array and allocates enough memory to hold 5 objects of Players_DB class.

it doesnt populate any of the members at all, so right now the array has no instances of Players_DB in it, you would have to add those by doing a

Players_DB_Arr[0] = new Players_DB();

or something along those lines for each of the indexes in the Array. And then obviously if you want to access those objects later you can by using their index again.

package myPackage;
import java.util.*;


public class Server {
public static void main(String[] args) 
{


List list_Players_DB = new ArrayList();


Players_DB Player = new Players_DB();
list_Players_DB.add(Player);
Players_DB Player1 = new Players_DB();
list_Players_DB.add(Player);
list_Players_DB.add("hmm");
for (int i=0; i < list_Players_DB.size();i ++)
{


System.out.println("Players_DB Object REF:" + list_Players_DB.get(i));
}




}
}

package myPackage;
import java.util.*;


public class Server {
public static void main(String[] args) 
{


List list_Players_DB = new ArrayList();


Players_DB Player = new Players_DB();
Player.player_id = 0;
list_Players_DB.add(Player.player_id);
Players_DB Player1 = new Players_DB();
Player1.player_id = 1;
list_Players_DB.add(Player1.player_id);
list_Players_DB.add("hmm");
for (int i=0; i < list_Players_DB.size();i ++)
{


System.out.println("Players_DB Object REF: " + list_Players_DB.get(i));
}




}
}

for (int i=0; i < list_Players_DB.size();i ++)
{
String obj_ref = list_Players_DB.get(i);
System.out.println(obj_ref.player_id);
}

Okay! So I tried out your method, this is giving me the results I want YES! XD

package myPackage;
import java.util.*;


public class Server {
public static void main(String[] args) 
{
//attempt 1
List list_Players_DB = new ArrayList();

System.out.println("Attempt 1:");
Players_DB Player = new Players_DB();
Player.player_id = 0;
list_Players_DB.add(Player.player_id);
Players_DB Player1 = new Players_DB();
Player1.player_id = 1;
list_Players_DB.add(Player1.player_id);
list_Players_DB.add("hmm");
for (int i=0; i < list_Players_DB.size();i ++)
{


System.out.println("Players_DB Object REF: " + list_Players_DB.get(i));
}




///Attempt 2


List<Players_DB> players = new ArrayList<Players_DB>();


players.add( new Players_DB());
players.add( new Players_DB());


Players_DB what = players.get(0);
Players_DB what1 = players.get(1);
System.out.println("");
System.out.println("");
System.out.println("Attempt 2:");
System.out.println(what);
System.out.println(what1);


}
}

Here's the results: