BlueJ trouble or program trouble (Combining Arraylists)

I'm doing is on BlueJ and it won't work. I've waited for 15 min. It compiles and there's no error when I hit main(), but it just keeps loading. Is it my code (does it have a super slow runtime?). If it is my code, I think that it is the way I combined the two Arraylists. Is there a better way to combine the lists is ascending order?

Code :

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import java.util.Scanner;
import java.io.*; 
import java.util.ArrayList;
public class MergeInventoriesTester
{
   private ArrayList<Product> Store1;
   private ArrayList<Product> Store2;
 
 
   private Product store1;
   private static Product store2;
   public static void main() throws FileNotFoundException
   {
       ArrayList<Product> Store1 = new ArrayList<Product>();
       ArrayList<Product> Store2 = new ArrayList<Product>();
 
       getTextFile(Store1, Store2);
       mergeArrayLists(Store1, Store2);
   }
   public static void getTextFile(ArrayList<Product> Store1, ArrayList<Product> Store2)throws FileNotFoundException
   {
       String id;
       String quantity;
       String unitPerPrice;
       Scanner inF = new Scanner(new File("C:\\Users\\Caili\\Documents\\Sophmore\\AP Computer Science\\Chapter 14\\Store1.txt"));
 
       while(inF.hasNextLine())
       {
           id = inF.nextLine();
           quantity = inF.nextLine();
           unitPerPrice = inF.nextLine();
           Store1.add(new Product(id, quantity, unitPerPrice));
       }
 
       Scanner inE = new Scanner(new File("C:\\Users\\Caili\\Documents\\Sophmore\\AP Computer Science\\Chapter 14\\Store2.txt"));
       while(inE.hasNextLine())
       {
           id = inE.nextLine();
           quantity = inE.nextLine();
           unitPerPrice = inE.nextLine();
           Store2.add(new Product(id, quantity, unitPerPrice));
       }
 
 
   }
   public static void mergeArrayLists(ArrayList<Product> Store1, ArrayList<Product> Store2) throws FileNotFoundException
   {
       ArrayList<Product> Merged = new ArrayList<Product>();
       int a = 0;;
       int b = 0;
       while(a < Store1.size()&& b < Store2.size())
       {
            if(Store1.get(a).returnID().compareTo(Store2.get(B).returnID())==1)
            {
                 Merged.add(Store1.get(a));
                 a++;
            }
 
            if(Store1.get(a).returnID().compareTo(Store2.get(B).returnID())==-1)
            {
                 Merged.add(Store2.get(B));
                 b++;
            }
 
            if(Store1.get(a).returnID().compareTo(Store2.get(B).returnID())==0)
            {
                Merged.add(Store1.get(a));
                a++;
                b++;
            }
 
       }
       for(int i=0; i<Merged.size();i++)
        {
            Product person = Merged.get(i);
            System.out.println(person.returnID());
        }
 
   }
}

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Code :

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public class Product
{
   private String id;
   private double quantity;
   private double unitPerPrice;
   private double value;
   public Product(String num,String amount,String perPrice)
   {
       id = num;
       quantity = Double.parseDouble(amount);
       unitPerPrice = Double.parseDouble(perPrice);
   }
   public String returnID()
   {
       return id;
   }
}

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Quote:

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it just keeps loading

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Do you mean the program goes into a loop and stops responding?
Otherwise please explain what "keeps loading" means.

Add some println statements that will show where the program is executing.

If you wanna merge 2 lists, why dont you just use:
Collections.copy(destinationList, sourceList);

Does the copy method merge or overlay the destination list?