سلام وقت بخیر بهروز جان

احتمالا جایی که حلقه for رو زدی در قسمت شرط جایی رو اشتباه تایپ کردی 

کد مربوطه رو ارسال کن تا این مورد رو بررسی کنم و راهنمایی بهتری داشته باشم

سلام پوریا جان 

این کد mainActivity :

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private RequestQueue requestQueue;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);
        View fabAddItemStudents = findViewById(R.id.fab_main_students);
        fabAddItemStudents.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this,AddNewStudentsActivity.class));
            }
        });
        StringRequest request = new StringRequest(Request.Method.GET,
               "http://expertdevelopers.ir/api/v1/experts/student" , new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
//              Log.i(TAG, "onResponse: " + response);
                try {
                List<Students> studentsList = new ArrayList<>();
                JSONArray jsonArrayAll = new JSONArray(response);
                for (int i = 0; i < response.length(); i++) {
                    Students students = new Students();
                   JSONObject jsonObjectItem = jsonArrayAll.getJSONObject(i);
                        students.setId(jsonObjectItem.getInt("id"));
                        students.setFirstName(jsonObjectItem.getString("first_name"));
                        students.setLastName(jsonObjectItem.getString("last_name"));
                        students.setCourse(jsonObjectItem.getString("course"));
                        students.setScore(jsonObjectItem.getInt("score"));
                  //  String date= jsonObjectItem.getString("created_at").substring(0,jsonObjectItem.getString("created_at").indexOf(" "));
                        students.setCreateDate(jsonObjectItem.getString("created_at"));
                        studentsList.add(students);
                    }
                    Log.i(TAG, "onResponse: "+studentsList.size());
                    RecyclerView recyclerView = findViewById(R.id.recycler_view_main_students);
                    recyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this,RecyclerView.VERTICAL,false));
                    recyclerView.setAdapter(new StudentAdapter(studentsList));
                }catch (JSONException e){
                    Log.e(TAG, "onResponse: " +e.toString() );
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e(TAG, "onErrorResponse: " +error.toString() );
            }
        });
        request.setTag(TAG);
        request.setRetryPolicy(new DefaultRetryPolicy(10000,3,2));
        requestQueue = Volley.newRequestQueue(this);
        requestQueue.add(request);
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        requestQueue.cancelAll(TAG);
    }
}