How to check if textfield is empty?

Y_Lakdime picture Y_Lakdime · Sep 30, 2015 · Viewed 67.6k times · Source

for my JavaFx application I want to check if the TextFields are empty, and if so, alert the user. These are the TextFields:

VBox fields = new VBox();  
Text usernametext = new Text("User name");
TextField user_name = new TextField();
Text firstnametext = new Text("First name");
TextField first_name = new TextField();
Text lastnametext = new Text("Last name");
TextField last_name = new TextField();
Text ibantext = new Text("IBAN");
TextField iban = new TextField();
Text passwordtext = new Text("Password");
TextField password = new TextField();
Text confirmpasstext = new Text("Confirm password");
TextField confirmpass = new TextField();
Button createBtn = new Button("Create account");

for now i just wanted to test the validation on one textfield. this is my validation function that is linked to the createBtn:

public void validation(){                

    if(user_name.getText().trim().isEmpty()){
        Alert fail= new Alert(AlertType.INFORMATION);
        fail.setHeaderText("failure");
        fail.setContentText("you havent typed something");
        fail.showAndWait();
    } else {
        Alert alert = new Alert(AlertType.INFORMATION);
        alert.setHeaderText("Succes");
        alert.setContentText("Account succesfully created!");
        alert.showAndWait();
    }
}

But I get this error message as i press the 'Create Account' button:

Exception in thread "JavaFX Application Thread" 

java.lang.NullPointerException
    at opdracht1.Opdracht1.validation(Opdracht1.java:36)
    at opdracht1.Opdracht1$2$1.handle(Opdracht1.java:103)
    at opdracht1.Opdracht1$2$1.handle(Opdracht1.java:98)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Node.fireEvent(Node.java:8411)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$355(GlassViewEventHandler.java:388)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)

Thanks in advance!

Answer

Alexander Ortiz picture Alexander Ortiz · Sep 30, 2015

First of all, check if user_name is not null. If it is not, you are setting a null text value to the JavaFX component somewhere in your code.

if(user_name.getText().trim().isEmpty()){

In any case, applying the trim() to a null value is what causes your exception. You should not need this (see Uluk Biy's comment to this answer), but considering you created a user_name TextField, you must check first if the getText() method is not null.

Something like this should do the trick:

if (user_name.getText() == null || user_name.getText().trim().isEmpty()) {
     // your code here
}