Data not getting displayed in Java FX Table when pressing button

Question

I am working with Table in Java FX. The code is below :

package addsubject;

import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.beans.property.SimpleStringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.TextField;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.control.cell.TextFieldTableCell;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.text.Font;
import javafx.stage.Stage;

public class AddSubject extends Application {

private TableView<Subject> table = new TableView<Subject>();
private final ObservableList<Subject> data
        = FXCollections.observableArrayList(new Subject("Mobile Computing", "5623"));
final HBox hb = new HBox();

public static void main(String[] args) {
    launch(args);
}

@Override
public void start(Stage stage) {
    Scene scene = new Scene(new Group());
    stage.setTitle("Add Subject");
    stage.setWidth(700);
    stage.setHeight(600);

    final Label label = new Label("Subject Details");
    label.setFont(new Font("Calibri", 20));

    table.setEditable(true);

    TableColumn sub = new TableColumn("Subject Name");
    sub.setMinWidth(400);
    sub.setCellValueFactory(
            new PropertyValueFactory<Subject, String>("sub"));
    sub.setCellFactory(TextFieldTableCell.forTableColumn());
    sub.setOnEditCommit(
            new EventHandler<TableColumn.CellEditEvent<Subject, String>>() {
                @Override
                public void handle(TableColumn.CellEditEvent<Subject, String> t) {
                    ((Subject) t.getTableView().getItems().get(
                            t.getTablePosition().getRow())).setSubName(t.getNewValue());
                }
            }
    );

    TableColumn code = new TableColumn("Subject Code");
    code.setMinWidth(150);
    code.setCellValueFactory(
            new PropertyValueFactory<Subject, String>("code"));
    code.setCellFactory(TextFieldTableCell.forTableColumn());
    code.setCellFactory(TextFieldTableCell.forTableColumn());
    code.setOnEditCommit(
            new EventHandler<TableColumn.CellEditEvent<Subject, String>>() {
                @Override
                public void handle(TableColumn.CellEditEvent<Subject, String> t) {
                    ((Subject) t.getTableView().getItems().get(
                            t.getTablePosition().getRow())).setSubCode(t.getNewValue());
                }
            }
    );

    table.setItems(data);
    table.getColumns().addAll(sub, code);

    final TextField addSubName = new TextField();
    addSubName.setPromptText("Subject Name");
    addSubName.setPrefWidth(350);

    final TextField addCode = new TextField();
    addCode.setPrefWidth(150);
    addCode.setPromptText("Subject Code");

    final Button addButton = new Button("Add");
    addButton.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent e) {
            data.add(new Subject(
                    addSubName.getText(),
                    addCode.getText()));
            addSubName.clear();
            addCode.clear();
        }
    });

    hb.getChildren().addAll(addSubName, addCode, addButton);
    hb.setSpacing(5);

    final VBox vbox = new VBox();
    vbox.setSpacing(10);
    vbox.setPadding(new Insets(10, 0, 0, 10));
    vbox.getChildren().addAll(label, table, hb);

    ((Group) scene.getRoot()).getChildren().addAll(vbox);

    stage.setScene(scene);
    stage.show();
}

public static class Subject {

    private final SimpleStringProperty sub;
    private final SimpleStringProperty code;

    private Subject(String subName, String subCode) {
        this.sub = new SimpleStringProperty(subName);
        this.code = new SimpleStringProperty(subCode);
    }

    public String getSubName() {
        return sub.get();
    }

    public void setSubName(String subName) {
        sub.set(subName);
    }

    public String getSubCode() {
        return code.get();
    }

    public void setSubCode(String subCode) {
        code.set(subCode);
    }
}
}

I will say its working.

1. When I run the code, the Table should contain one row of information which is stored in 'data'. It is not displayed in the table when I run the code. How can I make it displayed ?

2. Next thing is to add new data to the Table when the 'Add' button is pressed after filling the 2 TextFields. I filled the 2 Text Fields, pressed the button and nothing appeared in the Table. How can I make it appear ?

Answer 1

The PropertyValueFactories are wrong. For example

new PropertyValueFactory<Subject, String>("sub")

This means your data object should have a method getSub() to return the value. But yours is

public String getSubName() {
    return sub.get();
} 

Either rename the Getter to getSub() or use new PropertyValueFactory<Subject, String>("subName")

The same applies to subject code. You should read about JavaBeans naming conventions. Or this article on JavaFX Properties and Binding

Answer 2

Try implementing the following functions:

public StringProperty subProperty(){
    return sub;
}

public StringProperty codeProperty(){
    return code;
}

Why are these members final?