I am getting a NullPointerException when trying to use the Service class - multithreading

Question

I am getting a NullPointerException which is as follows:
java.lang.NullPointerException
file:/K:/Learner/JavaFx2/ProductApplication/dist/run166129449/ProductApplication.jar!/com/product/app/view/viewsingle.fxml
at com.product.app.controller.ViewSingleController.initialize(ViewSingleController.java:70)
at javafx.fxml.FXMLLoader.load(Unknown Source)
at javafx.fxml.FXMLLoader.load(Unknown Source)
And my ViewSingleController is as follows:
package com.product.app.controller;
import com.product.app.model.Product;
import com.product.app.service.ViewProductsService;
import com.product.app.util.JSONParser;
import com.product.app.util.TagConstants;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.ResourceBundle;
import javafx.collections.ObservableList;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.ProgressIndicator;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextField;
import javafx.scene.layout.Region;
import javafx.stage.Stage;
import javax.swing.JOptionPane;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONObject;
/**
* FXML Controller class
*
* #author Arun Joseph
*/
public class ViewSingleController implements Initializable {
private static String action = "";
#FXML
private TextField txtID;
#FXML
private TextField txtName;
#FXML
private TextField txtPrice;
#FXML
private TextArea txtDesc;
#FXML
private Region veil;
#FXML
private ProgressIndicator p;
private ViewProductsService service = new ViewProductsService();
private JSONObject product = null;
private JSONParser parser = new JSONParser();
private int pid = 1;
public void setPid(int pid) {
this.pid = pid;
}
/**
* Initializes the controller class.
*/
#Override
public void initialize(URL url, ResourceBundle rb) {
veil.setStyle("-fx-background-color: rgba(0, 0, 0, 0.4)");
p.setMaxSize(150, 150);
p.progressProperty().bind(service.progressProperty());
veil.visibleProperty().bind(service.runningProperty());
p.visibleProperty().bind(service.runningProperty());
Product product = new Product();
service.start();
ObservableList<Product> products = service.valueProperty().get();
products.get(pid);
txtID.textProperty().set(String.valueOf(products.get(pid).getPid()));
//product = service.valueProperty().get().get(pid);
//txtID.setText(String.valueOf(product.getPid()));
txtName.textProperty().set(product.getName());
txtPrice.textProperty().set(String.valueOf(product.getPrize()));
txtDesc.textProperty().set(product.getDescription());
}
private SomeService someService = new SomeService();
#FXML
private void handleUpdateButtonClick(ActionEvent event) {
action = "update";
someService.start();
p.progressProperty().bind(service.progressProperty());
veil.visibleProperty().bind(service.runningProperty());
p.visibleProperty().bind(service.runningProperty());
}
#FXML
private void handleDeleteButtonClick(ActionEvent event) {
action = "delete";
someService.start();
p.progressProperty().bind(service.progressProperty());
veil.visibleProperty().bind(service.runningProperty());
p.visibleProperty().bind(service.runningProperty());
}
#FXML
private void handleCancelButtonClick(ActionEvent event) {
closeStage();
}
private void closeStage() {
ViewSingleController.stage.close();
}
private static Stage stage = null;
public static void setStage(Stage stage) {
ViewSingleController.stage = stage;
}
private class SomeService extends Service<String> {
#Override
protected Task<String> createTask() {
return new SomeTask();
}
private class SomeTask extends Task<String> {
#Override
protected String call() throws Exception {
String result = "";
int success = 0;
List<NameValuePair> params = new ArrayList<NameValuePair>();
switch (action) {
case "update":
params.add(new BasicNameValuePair("pid", txtID.getText()));
params.add(new BasicNameValuePair("name", txtName.getText()));
params.add(new BasicNameValuePair("price", txtPrice.getText()));
params.add(new BasicNameValuePair("description", txtDesc.getText()));
product = parser.makeHttpRequest(TagConstants.url_update_product_with_id, "POST", params);
success = product.getInt(TagConstants.TAG_SUCCESS);
if (success == 1) {
result = "Successfully Updated the product";
JOptionPane.showMessageDialog(null, result);
closeStage();
}
break;
case "delete":
params.add(new BasicNameValuePair("pid", txtID.getText()));
product = parser.makeHttpRequest(TagConstants.url_delete_product_with_id, "POST", params);
success = product.getInt(TagConstants.TAG_SUCCESS);
if (success == 1) {
result = "Successfully Deleted the product";
JOptionPane.showMessageDialog(null, result);
closeStage();
}
break;
}
return result;
}
}
}
}
Please help me on how to fix this null pointer problem really help required. Thank you in advance

Answer 1

Inspect the line ViewSingleController.java:70. Put a breakpoint there. Run the program in a debugger and see what variables/fields are null.

Answer 2

The Exception happens on line 70, as you can see from the StackTrace.
On line 70, you call:
txtPrice.textProperty().set(String.valueOf(product.getPrize()));
The NullPointerException means that you are trying to access a method of an object that does not exist. Here, this might be txtPrice, textProperty, product or getPrize.
Skimming over your code, I'd guess it might be txtPrice, because you only set it as a member variable via
private TextField txtPrice;
but you never initialize it. Thus, txtPrice is null and txtPrice.textProperty().set will probably throw the NullPointer.