LinkedList with if statements? (Java)

So i got this one task to do, about LinkedList, you can take a look on my Main file

import java.util.*;

public class Main {
    public static void main(String[] args){
    
        ArrayList nokiaAL = new ArrayList();
        LinkedList phoneAL = new LinkedList();
        
        //input
        Smartphone a = new Smartphone("Nokia","Nokia 7 Plus",1300,260101);
        Smartphone b = new Smartphone("Samsung","Galaxy S8",900,220100);
        Smartphone c = new Smartphone("Xiaomi","Mi 10",1500,150031);
        Smartphone d = new Smartphone("Nokia","3310",250,101001);
        Smartphone e = new Smartphone("Samsung","Galaxy Y",400,774101);
        Smartphone f = new Smartphone("Apple","iPhone 7",1100,316300);
        
        phoneAL.insertAtFront(f);
        phoneAL.insertAtFront(e);
        phoneAL.insertAtFront(d);
        phoneAL.insertAtFront(c);
        phoneAL.insertAtFront(b);
        phoneAL.insertAtFront(a);
        
        //process
        Object r = (Object) phoneAL.getFirst();
        while (r != null) {
            System.out.print(" "+r);
            r = (Object) phoneAL.getNext();
        }
        
        //The conditions
        //If nokia + the price $1200+, it will save all the info about nokia
        //If brand samsung + model Galaxy Y, It will count the total of the phone
        Object obj;
        int countSamsung = 0;
        for(int i=0;i<phoneAL.size();i++){
            obj = phoneAL.get(i);
            Smartphone obj2 = (Smartphone) obj;
            if(obj2.getBrand().equalsIgnoreCase("Nokia")){
                nokiaAL.add(obj2);
            }
            if(obj2.getBrand().equalsIgnoreCase("Samsung")){
                if(obj2.getModel().equalsIgnoreCase("Galaxy Y")){
                    countSamsung++;
                }
            }
        }
        
        //output
        System.out.println("\n");
        System.out.println("Details about Nokia phone more than RM1200:"+nokiaAL.toString());
        System.out.println("Quantity of Samsung model Galaxy Y: " + countSamsung);
    }
}

I know how to print all the details in the LinkedList, the main point here is, you can't add or change anything of other .java files, you can only edit the Main.java file, is it even possible? here's my Smartphone and LinkedList code.

public class Smartphone {
    
    String brand;//e.g: Nokia, Samsung
    String model;//e.g: Lumia, Galaxy Y, Note S
    double price;
    int warranty;//warranty (in year)

    Smartphone() {
        
    }
    
public Smartphone(String a, String b, double c, int d){
    this.brand=a;
    this.model=b;
    this.price=c;
    this.warranty=d;
}    

public String getBrand(){
    return brand;
}

public String getModel(){
    return model;
}

public double getPrice(){
    return price;
}

public int getWarranty(){
    return warranty;
}

public String toString(){
    return "\n\nBrand: "+brand +"\nModel: "+ model +"\nPrice: $"+ price +"\nWarranty: "+ warranty;
    }
}

public class LinkedList 
{
   private Node first;
   private Node last;
   private Node current; 
   
    public LinkedList()
    {
        first = null;
                last = null;
                current = null;  
    }
    
    public boolean isEmpty(){   
            return (first == null); }   
    
    public void insertAtFront(Object insertItem){
            Node newNode = new Node(insertItem);
       
      
            if (isEmpty()){
        first = newNode;
        last = newNode;
      }else{
          newNode.next = first;
          first = newNode;
      }
    }
        public void insertAtBack(Object insertItem){
            Node newNode = new Node(insertItem);
        
        if(isEmpty()){
            first = newNode;
            last = newNode;
        }else{
            last.next = newNode;
            last = newNode;
        }
    }
        public Object removeFromFront(){
            Object removeItem = null;
        
        if(isEmpty()){
            return removeItem;
        }
        
        removeItem = first.data;
        
          if(first == last){
            first = null;
            last = null;
            }else
            first = first.next;
           
    return removeItem;
    }
    
    public Object removeFromBack(){
    Object removeItem = null;
        
      if(isEmpty())
      {
        return removeItem;
      }
        
      removeItem = last.data;
          
        if (first == last)
      {
         first = null;
         last = null;
      }else{
         current = first;
         while(current.next != last)
            current = current.next;
         last = current;
         last.next = null;
        }
        
      return removeItem;
     }
     
     public Object getFirst(){
        if(isEmpty())
          return null;
        else
        {
            current = first;
            return current.data;
        }
    }
     
     public Object getNext(){
        if(current == last)
          return null;
        else
        {
            current = current.next;
            return current.data;
        }
    }    
}

As I said before, I can print all the details of the phones, but how to really use it as conditions, like If-else statement? for example, if(obj.getBrand().equalsIgnoreCase("Nokia")){} , I can achieve this with ArrayList but since this is LinkedList task, So I'm still figuring this out without even know if its possible or not. I hope someone would understand this and able to help. TQ

here's my node code for the LinkedList

public class Node {
    Object data;
    Node next;
    
    Node(Object obj){
        data=obj;
    }
}