A Problem related to mysql database and nullpointerexception

问题

I made a JavaFX Application, and its GUI has these four following things:

A TextField, called name (takes in the username)
A PasswordField, called password (takes in the password)
A ToggleGroup, called gender (there's a method related to this ToggleGroup (male,female,other))
A TextField, called locationField (takes in the location name)

There is a sign up button at the bottom that takes all the data and saves it into the MySQL database

Here's the method related to the ToggleGroup

public String getGender() {
    String gen = "";
    if (male.isSelected()) {
        gen = "Male";
    } else if (female.isSelected()) {
        gen = "Female";
    } else if (other.isSelected()) {
        gen = "Other";
    }
    return gen;
}

Here's the eventhandler for the sign up button:

 @FXML
 public void signUP() throws SQLException{
    progress.setVisible(true);
    PauseTransition pt = new PauseTransition();
    pt.setDuration(Duration.seconds(3));
    pt.setOnFinished(e -> System.out.println("Sign Up Successful!"));
    pt.play();

String url = "jdbc:mysql://localhost:3306/genius";
    String user = "root";
    String password = "$Can$123";
    String sql = "insert into coders(names,password,gender,address)" + "values (?,?,?,?)";
    try {
        connection = DriverManager.getConnection(url, user, password);
        pst = connection.prepareStatement(sql);
        pst.setString(1, name.getText());
        pst.setString(2, password);
        pst.setString(3, getGender());
        pst.setString(4, locationField.getText());
        pst.executeUpdate();
    } catch (NullPointerException e) {
        e.printStackTrace();
    }
}

Here's the problem I'm facing: when I enter all the following details and then I click the signup button, it shows me this error:

java.lang.NullPointerException
at GaveUp/sample.SignUpController.signUP(SignUpController.java:83)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke
    (NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke
    (DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke
    (DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1784)
at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent
    (CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent
    (EventHandlerManager.java:238)
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:8879)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:200)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased
    (ButtonBehavior.java:206)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord
    .handleBubblingEvent (CompositeEventHandler.java:218)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent
    (CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent
    (EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent
    (EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent
    (CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent
    (BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent
    (EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent
    (BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent
    (EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent
    (BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent
    (EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3851)
at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run
    (GlassViewEventHandler.java:397)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run
    (GlassViewEventHandler.java:295)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2
    (GlassViewEventHandler.java:434)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock
    (QuantumToolkit.java:390)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent
    (GlassViewEventHandler.java:433)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:835)

Under the NullPointerException, there's a line which says:

at GaveUp/sample.SignUpController.signUP(SignUpController.java:83)

which is reffering to the lines of the sign up button method which says:

pst.setString(1, name.getText());
pst.setString(3, getGender());
pst.setString(4, locationField.getText());

How should I fix this error. Any help would be appreciated, Thank you!

来源：https://stackoverflow.com/questions/61150218/a-problem-related-to-mysql-database-and-nullpointerexception

标签

java

mysql

nullpointerexception

javafx-11

java-12