Getting the value inside the inner class

How will I get the value inside the inner class in Android Studio 4.0.1. I tried to declare a global variable but still it doesn't work. I also tried this one declaring a final array but I still cannot get the value

public class FetchData {
    private Context con;

    public FetchData(Context con){
        this.con = con;
    }

    public String getPatientIDFromDatabase(){
        final String[] id = {""};
        StringRequest strRequest = new StringRequest(Request.Method.POST, "http://192.168.254.199/projects/AndroidServers/TheMedicalGCs/GetPatientID.php",
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        try{
                            JSONObject jsonObject = new JSONObject(response);
                            id[0] = jsonObject.getString("PatientID");
                        }
                        catch (Exception e){
                            Toast.makeText(con, e.getMessage(), Toast.LENGTH_SHORT).show();
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(con, error.getMessage(), Toast.LENGTH_SHORT).show();
                    }
                }
        );
        Volley.newRequestQueue(con).add(strRequest);

        return id[0];
    }
}

I just want that method to return the value comes from the JSON.

You can declare that as a static variable,

static final String[] id = {""};

I have removed constructor for your classFetchData and moved it as parameter to method getPatientIDFromDatabase(Context context). So the looks like this.

public class FetchData {

    public static String getPatientIDFromDatabase(Context context) {

        final String[] id = {""};

        StringRequest strRequest = new StringRequest(Request.Method.POST,
                "http://192.168.254.199/projects/AndroidServers/TheMedicalGCs/GetPatientID.php",
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        try {
                            JSONObject jsonObject = new JSONObject(response);
                            id[0] = jsonObject.getString("PatientID");
                        } catch (Exception e) {
                            Toast.makeText(context, e.getMessage(), Toast.LENGTH_SHORT).show();
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(context, error.getMessage(), Toast.LENGTH_SHORT).show();
                    }
                }
        );
        Volley.newRequestQueue(context).add(strRequest);

        return id[0];
    }
}

Now let's the value it is returning from FetchData class, but if you want other classes to get access to the return value, you need to method as static. Which i already added above.

Now let's get string value from other class named HomeActivity:

String value = FetchData.getPatientIDFromDatabase(context)

I already fixed the problem by declaring the final String[] id = {""} into a member variable and declare it as private String id only. I remembered that you cannot access the variable that is not declared as final inside the inner class.

public class FetchData {
    private Context con;
    private String id;

    public FetchData(Context con){
        this.con = con;
    }

    public String getPatientIDFromDatabase(){
        StringRequest strRequest = new StringRequest(Request.Method.POST, "http://192.168.254.199/projects/AndroidServers/TheMedicalGCs/GetPatientID.php",
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        try{
                            JSONObject jsonObject = new JSONObject(response);
                            id = jsonObject.getString("PatientID");
                        }
                        catch (Exception e){
                            Toast.makeText(con, e.getMessage(), Toast.LENGTH_SHORT).show();
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(con, error.getMessage(), Toast.LENGTH_SHORT).show();
                    }
                }
        );
        Volley.newRequestQueue(con).add(strRequest);

        return id;
    }
}