How do I import a populated ready-made ArrayList from another class in java?

I'm working with a large set of imported data and retrieving certain parts of it in the main method with 2 classes(WeatherStation, WeatherReading).The data is temperature readings at loads of weather stations(station id, name, lat, lon, year, time, temp etc) I made a third class (SoloSiteIds) whose sole purpose was to return a whole and complete ArrayList of the site ids with no duplication. But I cannot import the ArrayList from the other class into my main method. My SoloSiteIds class looks like this:

public class SoloSiteIds {

 static ArrayList <Integer> siteIds = new ArrayList <Integer>();
 

 public SoloSiteIds() {
 }
 
 public SoloSiteIds( ArrayList <Integer> siteIds) {
	 
	 String[] weatherData = WeatherData.getData();{ // get the weather data 
	 
		 for (int i = 1; i < weatherData.length; i++) {
				String line = weatherData[i];
				String[] elements = line.split(","); // Split the data at ",
				
				String siteid = elements[0]; // convert all the site id's at index 0 to integers
				int id = Integer.parseInt(siteid);
				if(!siteIds.contains(id)) {
					siteIds.add(id);
				}
	 
	 
	 this.siteIds=siteIds;



		 }
	
}
}

public static ArrayList<Integer> getSiteIds() {
	return siteIds;
}

public ArrayList<Integer> setSiteIds(ArrayList<Integer> siteIds) {
	return this.siteIds = siteIds;
}	

}

The main method where I am trying to import the ArrayList "siteIds" looks like this:

		WeatherStation thisStation = new WeatherStation (id, name, lat, lon);
	WeatherReading thisReading = new WeatherReading(year, month, date, hour, windSpeed, temp);
	SoloSiteIds siteList= new SoloSiteIds();
	


	
	String[] weatherData = WeatherData.getData();{ // get the weather data

		
		for (int i = 1; i < weatherData.length; i++) {
			String line = weatherData[i];
			String[] elements = line.split(","); // Split the data at ","	
			
	
			
				

					String siteid = elements[0]; // convert all the site id's at index 0 to integers
					id = Integer.parseInt(siteid);
					thisStation.setId(id);
					
					thisStation.setName(elements[1]);
					
					//parse the different elements into different data types
					
					String stringLat = elements[2];    
					lat= Double.parseDouble(stringLat);
					lat = thisStation.setLat(lat);
					lat=thisStation.setLat(lat);
						
					String stringLon = elements[3];
					lon= Double.parseDouble(stringLon);
					lat = thisStation.setLon(lon);
					lat=thisStation.setLon(lon);
					
					String stringTemp=elements[9];
					temp=Double.parseDouble(stringTemp);
					temp=thisReading.setTemp(temp);

Only the top part is relevant. I have tried lots of different variation of .set and .get using "thisList" instance and a new ArrayList like

ArrayList<Integer> siteIds = thisList.setSiteIds();
ArrayList<Integer> siteIds= SoloSiteIds.getSiteIds();
thisList=Siteids.setSiteIds();
thisList=SingleSoloSites.setSiteIds();

etc etc. This might look stupid but im just showing Ive tried numerous things and i am stuck
Thanks

I believe your problem is that you are initializing siteIds as an empty Arry list but you are not setting the data in a static way (the set Method is not static).

As far as I am aware of your situation, I belive that the SoloSiteIds class is unnescessary. I would solve your problem with an ArrayList declared in your main class and initialize with a getSoleIds() method also declared in your main class.
The getSoleIds() Method should contain the code currently in the SoleSiteIds initializer.