TextArea getter from controller class gives NullPointerException - javafx

Question

i have a simple javafx FXML app
that has a button and a textArea
I am trying to write to the textArea from another
class (not the controller)
without sending the textArea
to that class ,
i added a getter on my controller class,
and on the writingClass i created an object of the ControllerClass
and then trying to write to the textArea ,
i am getting a java.lang.NullPointerException and java.lang.reflect.InvocationTargetException
what am i doing wrong ???
//Controller.java
package sample;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.TextArea;
public class Controller {
#FXML
Button myButton;
#FXML
TextArea myTextArea;
WriteToTextArea writeToTextArea;
public TextArea getMyTextArea() {
return myTextArea;
}
public void buttonPressed() {
writeToTextArea = new WriteToTextArea();
writeToTextArea.writeThis("trying To Write To TextArea");
}
}
//WriteToTextArea.java
package sample;
import javafx.scene.control.TextArea;
public class WriteToTextArea {
private Controller objectController;
private TextArea textArea;
public WriteToTextArea() {
objectController = new Controller();
textArea = new TextArea();
textArea = objectController.getMyTextArea();
}
public void writeThis(String whatToWrite) {
textArea.setText(whatToWrite);
}
}

Answer 1

The textArea is initialized in the controller by the FXMLLoader when the FXML file is loaded. It is only initialized in the controller, and won't be initialized in other instances of the same class (what would it be initialized to?). So when you create a new Controller instance with
objectController = new Controller();
the textArea in that instance is null, so when you call
textArea.setText(whatToWrite);
you get a null pointer exception.
You need the WriteToTextArea instance to have a reference to the controller itself, not some arbitrary instance of the same class. You can do this by passing a reference to the controller to the WriteToTextArea constructor:
package sample;
import javafx.scene.control.TextArea;
public class WriteToTextArea {
private Controller objectController;
private TextArea textArea;
public WriteToTextArea(Controller objectController) {
this.objectController = objectController ;
textArea = objectController.getMyTextArea();
}
public void writeThis(String whatToWrite) {
textArea.setText(whatToWrite);
}
}
and then in the controller code
public void buttonPressed() {
writeToTextArea = new WriteToTextArea(this);
writeToTextArea.writeThis("trying To Write To TextArea");
}