how can i retrieve data from firestore and store it in a object class the a public list

Question

i am trying to retrieve data from firestore and add it to an object class Trade then adding trade to a public list then display, but its not displaying anything.

my list handler class:

public class ListHandler {
    public static List<Trade> ListTrades = new ArrayList<Trade>();
}

my trade obj class:

public class Trade implements Serializable {

    public Trade(String name, String surname, String description, String phone) {
        Name = name;
        Surname = surname;
        Description = description;
        Phone = phone;
    }

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        Name = name;
    }

    public String getSurname() {
        return Surname;
    }

    public void setSurname(String surname) {
        Surname = surname;
    }

    public String getDescription() {
        return Description;
    }

    public void setDescription(String description) {
        Description = description;
    }

    public String getPhone() {
        return Phone;
    }

    public void setPhone(String phone) {
        Phone = phone;
    }

    String Name, Surname, Description, Phone;

    public Trade() {

    }

my code for retrieving data:

public void onClick(View v)
    {
   
     getData();

        Intent Job = new Intent(Post.this,MainActivity.class);

        startActivity(Job);

    }
});
void getData(){
    db.collection("Posts").get().addOnCompleteListener(
            new OnCompleteListener<QuerySnapshot>() {
                @Override
                public void onComplete(@NonNull Task<QuerySnapshot> task) {
                    if(task.isSuccessful()){
                        //List<Trade> ListTrade = new ArrayList<Trade>();
                        for(QueryDocumentSnapshot document : task.getResult() ){
                            Log.d(TAG, document.getId() + "=>" + document.getData());

                            Map<String, Object> data = document.getData();

                            String Name = (String) data.get("Name");
                            String Surname = (String) data.get("Surname");
                            String Phone = (String) data.get("Phone");
                            String Description = (String) data.get("Description");

                            if(Name != null ){
                                Trade Service = new Trade(Name,Surname,Phone,Description);
                                ListHandler.ListTrades.add(Service);

                            }else{
                                Log.d(TAG, "Got Bad Data for " + document.getId() + " => " + document.getId());
                            }

                        }


                    }else{
                        Log.d(TAG, "Error getting document: ", task.getException());
                    }

                }
            });

my main class which displays:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    txtDisplay = findViewById(R.id.txtDisplay);

    btnPost1 = findViewById(R.id.btnPost);
    btnPost1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v)
        {
            Intent Job = new Intent(MainActivity.this,Post.class);

            startActivity(Job);
        }
    });

    if (!ListHandler.ListTrades.isEmpty())
    {  String Text ="" ;
        for (Trade Output: ListHandler.ListTrades)
        {
            Text+= Output.Name+"\n"+Output.Surname+"\n"+Output.Phone+"\n"+Output.Description+"\n\n";
        }
        txtDisplay.setText(Text);
    }



}