Thread: Help making and iterating through ArrayList (Java Beginner)

I am trying to make a list that contains four variable (integer, double, double, string). I need to create two methods. One method to add another entry to the list (but only if the integer variable is unique in the list), and another method that removes a specified entry (again, based on integer variable) from the list. I am having a lot of trouble setting up the ArrayList so that I can iterate through it in order to implement these two methods (I've tried a bunch of approaches, but nothing seems to be doing the trick). I appreciate any help with what I'm doing wrong!

ArrayList collection=new ArrayList(); 	//initialization of trade collection
 
 
	public void addTrade(int identifier, double amount, double rate, String currency){
		//addTrade: inserts a single FXTrade instance into the collection
		for (int i = 0; i < collection.size(); i++){
			//ensure the instance is unique before adding to the list
 
			Object currElement = collection.get(i);
			if (currElement == collection(identifier, amount, rate, currency)){  //don't add the new trade instance if it's already in the collection
				continue;
			}else {
				collection.add(identifier, amount, rate, currency);
			}		
		}
	}
 
 
	public void removeTrade(int identifier){
		//removeTrade: removes a single FXTrade instance from the collection
 
		//search collection for requested trade; remove the requested trade (if it's in the collection)
		for (int i = 0; i < collection.size(); i++){
			if (collection.get(i)==identifier){
				collection.remove(i);
				break;  //once the trade is removed, stop iteration (uniqueness was checked in addTrade method)
			}
		}
	}

Could you give me an example of how to do that? I am trying to input and store those four pieces of information, and am stuck on how to go about doing it.