Hjälp med felmeddelande, JAVA

1#:-Jag håller för att lösa en övning i JavaFX.

Jag ska göra tre knappar, Update, Add och Delete. Så länge jag har gjort Add- och Delete-knappar. Add fungerar ok. Men när jag trycker på Delete-knapp då får jag fel meddelande 'NullPointerException'. Min kod är bild på två separat filer. En filen som har ’main’ command line metod som kör programmet (UPPGIFT4D_Personhanteraren.java) och den andra filen som anropar som objekt av den första (Person.java). Här kommer det båda två filer i tur ordning och den felmeddelande efter:

1#:-FIL (UPPGIFT4D_Personhanteraren.java):

package application;

import java.util.Arrays;

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.geometry.*;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.control.TableView.TableViewSelectionModel;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.*;
import javafx.scene.text.*;
import javafx.stage.Stage;

/**
* @author Carlos 12/19/2020
*
*/
public class UPPGIFT4D_Personhanteraren extends Application {

private final TableView<Person> table = new TableView<>();
private final ObservableList<Person> personManagerList = FXCollections.observableArrayList();

final VBox root = new VBox();

public static void main(String[] args) {
System.out.println("UPPGIFT#4:- JavaFX with Serialition. This program will"
+ "management the people behavior:\n");

Application.launch();

}

//Define the button cell.

@SuppressWarnings("unchecked")

@Override
public void start(Stage stage) {

stage.setTitle("JavaFX GridPane and Table LAYOUT");

/**
* TODO Turn on multi-row selection for the TableView.
*/
TableViewSelectionModel tsm = table.getSelectionModel();
tsm.setSelectionMode(SelectionMode.MULTIPLE);

stage.setWidth(800);
stage.setHeight(800);

table.setEditable(true);

table.setColumnResizePolicy(TableView.CONSTRAINED_RESIZE_POLICY);
table.setPlaceholder(new Label("No visible columns and/or data exist."));

/**
* § Connection 'GridPane' with 'Table'
*/
GridPane gridPaneTable = this.createGridPane();// § Connection 'GridPane' with 'Table'

root.setSpacing(5);
root.setPadding(new Insets(10, 0, 0, 10));
root.getChildren().addAll(gridPaneTable, table);

root.setSpacing(5);

root.setStyle("-fx-padding: 10; -fx-border-style: solid inside;"
+ "-fx-border-width: 2;"
+ "-fx-border-insets: 5;"
+ "-fx-border-radius: 5;"
+ "-fx-border-color: blue;");

/**
* TO CREATE: Create the Scene.
*/
Scene scene = new Scene(root);

final Label label = new Label("");
label.setFont(new Font("Arial", 20));

table.setEditable(true);

TableColumn<Person, String> firstNameCol = new TableColumn("First Name");
firstNameCol.setMinWidth(100);
firstNameCol.setCellValueFactory(new PropertyValueFactory<>("firstName"));

TableColumn lastNameCol = new TableColumn("Last Name");
lastNameCol.setMinWidth(100);
lastNameCol.setCellValueFactory(new PropertyValueFactory<>("lastName"));

TableColumn aGeCol = new TableColumn("Age");
aGeCol.setMinWidth(100);
aGeCol.setCellValueFactory(new PropertyValueFactory<>("email"));

table.setItems(personManagerList);

/**
* ADD: Add columns to the TableView.
*/
table.getColumns().addAll(firstNameCol, lastNameCol, aGeCol);

final TextField addFirstName = new TextField();
addFirstName.setPromptText("First Name");
addFirstName.setMaxWidth(firstNameCol.getPrefWidth());

final TextField addLastName = new TextField();
addLastName.setMaxWidth(lastNameCol.getPrefWidth());
addLastName.setPromptText("Last Name");

final TextField addAge = new TextField();
addAge.setMaxWidth(aGeCol.getPrefWidth());
addAge.setPromptText("Age");

stage.setScene(scene);

stage.show();

}

@SuppressWarnings({ "rawtypes", "unchecked" })
public GridPane createGridPane() {

GridPane grid = new GridPane();
grid.setPadding(new Insets(10));
grid.setHgap(10);
grid.setVgap(10);

Text txt = new Text("PERSON MANAGER");
txt.setFont(Font.font("Dialog", FontWeight.BOLD, 12));

grid.add(txt, 0, 0, 1, 1);
grid.add(new Separator(), 0, 1, 3, 1);

grid.add(new Label("First name"), 0, 2, 1, 1);
TextField addFirstName;
grid.add(addFirstName = new TextField(), 1, 2, 1, 1);

grid.add(new Label("Last name"), 0, 3, 1, 1);
TextField addLastName;
grid.add(addLastName = new TextField(), 1, 3, 1, 1);

grid.add(new Label("Age"), 0, 4, 1, 1);
TextField addAge;
grid.add(addAge = new TextField(), 1, 4, 1, 1);

grid.add(new Separator(), 0, 5, 3, 1);

FlowPane fp = new FlowPane(Orientation.HORIZONTAL, 10, 10);
fp.setAlignment(Pos.CENTER_RIGHT);

Button updateButton;
Button addButton;
Button deleteButton;

fp.getChildren().addAll(updateButton = new Button("Update"),
addButton = new Button("Add"),
deleteButton = new Button("Delete"));
grid.add(fp, 0, 6, 3, 1);

/**
* PUT IN ACTION The ' Add' button.
*/
addButton.setOnAction((ActionEvent e) -> {
personManagerList.add(new Person(addFirstName.getText(),
addLastName.getText(),
addAge.getText()));
addFirstName.clear();
addLastName.clear();
addAge.clear();

});

/**
* The first way to delete action.
*/
deleteButton.setOnAction(new EventHandler() {

@Override
public void handle(Event e) {
// TODO Auto-generated method stub
deletePerson(); // ERROR...ERROR...ERROR...ERROR...ERROR...ERROR

}

});

return grid;

}

/**
* DECLARE 'deletePerson' method.
*/
public void deletePerson() {

TableViewSelectionModel<Person> tsm = table.getSelectionModel();//Original shows so 'TableViewSelectionModel tsm ='

// Check, if any rows are selected.
if (tsm.isEmpty()) {

System.out.println("Please select a row to delete.");
return;

}

// Get all selected row indices in an array.
ObservableList<Person> list = tsm.getSelectedItems();

// TODO
System.out.println("\nThe table elemens are: " + tsm.getSelectedItems());

Integer[] selectedIndices = new Integer[list.size()];

// Sort the array
Arrays.sort(selectedIndices);

// Delete rows (last to first)
for(int i = selectedIndices.length - 1; i >= 0; i--) {
//TODO Print out
System.out.println("\nThe table element are: " + selectedIndices[i].intValue());
tsm.clearSelection(selectedIndices[i].intValue());// ERROR...ERROR...ERROR
table.getItems().remove(selectedIndices[i].intValue());

}

}

}

2#:-FIL (UPPGIFT4D_Person.java):

package application;

import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

public class Person {

/**
* SOLUTION to the problem can not retrieve property.
*/
// private final SimpleStringProperty firstName; // SOURCE TO THE PROBLEM.
private StringProperty firstName = new SimpleStringProperty();
public final StringProperty firstNameProperty() {
return firstName;
}

public final String getFirstName() {
return firstName.get();
}

public final void SetFirstName(String value) {
firstName.set(value);
}

private final SimpleStringProperty lastName;
private final SimpleStringProperty email;

Person(String fName, String lName, String email) {

this.firstName = new SimpleStringProperty(fName);
this.lastName = new SimpleStringProperty(lName);
this.email = new SimpleStringProperty(email);

}

public String getFirsName() {
return firstName.getName();
}

public void setFirsName(String fName) {
this.firstName.setValue(fName);
}

public String getLastName() {
return lastName.get();
}

public void setLastName(String lName) {
this.lastName.set(lName);
}

public String getEmail() {
return email.get();
}
public void setEmail (String emailA) {
email.set(emailA);
}
}

3#:-Fel meddelande:

UPPGIFT#4:- JavaFX with Serialition. This program willmanagement the people behavior:

Please select a row to delete.
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at application.UPPGIFT4D_Personhanteraren.deletePerson(UPPGIFT4D_Personhanteraren.java:321)
at application.UPPGIFT4D_Personhanteraren$1.handle(UPPGIFT4D_Personhanteraren.java:219)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8886)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3856)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1851)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2584)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:409)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:299)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:447)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:412)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:446)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:832)

The table elemens are: [application.Person@2bb27d5]

Jag undrar vad denna felmeddelande betyder och varför?