Why am I getting a Null Pointer Exception when I add data on ArrayList in JavaFX

Question

So I am trying to create a javafx program where I can sign up as a patient. I don't know how to save data yet so I will be using an array list. I have declared an arraylist of patient on the sign up controller class and created a method to store data. But whenever I try to run the program I always get the "Find why this could be null". I don't know what is the reason behind this.

Here is my code:

public void signUpClicked() throws IOException {
    boolean isEmpty = false;
    if(namePt.getText().equals("")){
        namePt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        namePt.setStyle(null);
    }
    if(agePt.getText().equals("")){
        agePt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        agePt.setStyle(null);
    }
    if(genderPt.getText().equals("")){
        genderPt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        genderPt.setStyle(null);
    }
    if(addressPt.getText().equals("")){
        addressPt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        addressPt.setStyle(null);
    }
    if(emailPt.getText().equals("")){
        emailPt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        emailPt.setStyle(null);
    }
    if(usernamePt.getText().equals("")){
        usernamePt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        usernamePt.setStyle(null);
    }
    if(passwordPt.getText().equals("")){
        passwordPt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        passwordPt.setStyle(null);
    }
    if(confirmPasswordPt.getText().equals("")){
        confirmPasswordPt.setStyle("-fx-border-color: red; -fx-border-width: 2px;");
        signUpWarningPt.setText("Incomplete information!");
        isEmpty=true;
    }
    else {
        signUpWarningPt.setStyle(null);
        confirmPasswordPt.setStyle(null);
    }
    if(!isEmpty && checkPassword(passwordPt.getText(),confirmPasswordPt.getText())){
        recordLoginInfo(usernamePt.getText(),passwordPt.getText(),"PatientLoginInfo.txt");
        addPatientInfo(namePt.getText(),agePt.getText(),genderPt.getText(),addressPt.getText(),usernamePt.getText(),passwordPt.getText());
        setDetails();
    }
}

This is the variables I created:

static ArrayList<Patient> patientList;

    @FXML private TextField namePt;
    @FXML private TextField agePt;
    @FXML private TextField genderPt;
    @FXML private TextField addressPt;
    @FXML private TextArea concernsPt;
    @FXML private TextField emailPt;
    @FXML private TextField usernamePt;
    @FXML private TextField passwordPt;
    @FXML private TextField confirmPasswordPt;
    @FXML private Button signupBtnPt;
    @FXML private Button closeBtnPt;
    @FXML private Hyperlink patientLoginLink;
    @FXML private Label signUpWarningPt;

This is the method I created for adding data on the arraylist:

 public void addPatientInfo(String name, String age, String gender, String address,String username, String password){
        Patient p = new Patient(name,age,gender,address,username,password);
        patientList.add(p);
    }

Here is the patient class:

public class Patient implements Serializable {
    private String name;
    private String age;
    private String gender;
    private String address;
    
    private String username;
    private String password;
   

    public Patient(String name, String age, String gender, String address, String username, String password) {
        this.name = name;
        this.age = age;
        this.gender = gender;
        this.address = address;
        this.username = username;
        this.password = password;
    }
}

And lastly the error message I always get:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1862)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1729)
    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:8889)
    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$3(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1859)
    ... 46 more
Caused by: java.lang.NullPointerException: Cannot invoke "java.util.ArrayList.add(Object)" because "Controllers.PatientSignupController.patientList" is null
    at Controllers.PatientSignupController.addPatientInfo(PatientSignupController.java:118)
    at Controllers.PatientSignupController.signUpClicked(PatientSignupController.java:111)
    ... 57 more

patientList must be initialized, `patientList = new ArrayList()` — Igmer Rodriguez, May 24 '21 at 14:32
@James_D above the signUpClicked() method it is on the sign up class. — akolangto, May 24 '21 at 14:33
There's nowhere in the code you posted that you created/initialized the list. — James_D, May 24 '21 at 14:34
oh that's it! I always forget to initialize array lists. My bad i am only a beginner — akolangto, May 24 '21 at 14:36
If you've seen the mistake before, just [reading the stack trace](https://stackoverflow.com/q/3988788/2775450) will point you to the exactly what's wrong, and you can fix it without all the extra work of posting here. — James_D, May 24 '21 at 14:46

Why am I getting a Null Pointer Exception when I add data on ArrayList in JavaFX

0 Answers0