~/Desktop $ javac HelloWorld.java
HelloWorld.java:3: error: package javafx.application does not exist
import javafx.application.Application;
^
HelloWorld.java:4: error: package javafx.event does not exist
import javafx.event.ActionEvent;
^
HelloWorld.java:5: error: package javafx.event does not exist
import javafx.event.EventHandler;
^
HelloWorld.java:6: error: package javafx.scene does not exist
import javafx.scene.Scene;
^
HelloWorld.java:7: error: package javafx.scene.control does not exist
import javafx.scene.control.Button;
^
HelloWorld.java:8: error: package javafx.scene.layout does not exist
import javafx.scene.layout.StackPane;
^
HelloWorld.java:9: error: package javafx.stage does not exist
import javafx.stage.Stage;
^
HelloWorld.java:11: error: cannot find symbol
public class HelloWorld extends Application {
^
symbol: class Application
HelloWorld.java:17: error: cannot find symbol
public void start(Stage primaryStage) {
^
symbol: class Stage
location: class HelloWorld
HelloWorld.java:13: error: cannot find symbol
launch(args);
^
symbol: method launch(String[])
location: class HelloWorld
HelloWorld.java:16: error: method does not override or implement a method from a supertype
@

^
HelloWorld.java:19: error: cannot find symbol
Button btn = new Button();
^
symbol: class Button
location: class HelloWorld
HelloWorld.java:19: error: cannot find symbol
Button btn = new Button();
^
symbol: class Button
location: class HelloWorld
HelloWorld.java:21: error: cannot find symbol
btn.setOnAction(new EventHandler<ActionEvent>() {
^
symbol: class EventHandler
location: class HelloWorld
HelloWorld.java:21: error: cannot find symbol
btn.setOnAction(new EventHandler<ActionEvent>() {
^
symbol: class ActionEvent
location: class HelloWorld
HelloWorld.java:29: error: cannot find symbol
StackPane root = new StackPane();
^
symbol: class StackPane
location: class HelloWorld
HelloWorld.java:29: error: cannot find symbol
StackPane root = new StackPane();
^
symbol: class StackPane
location: class HelloWorld
HelloWorld.java:31: error: cannot find symbol
primaryStage.setScene(new Scene(root, 300, 250));
^
symbol: class Scene
location: class HelloWorld
18 errors