Designing Graphical Interfaces - Beginning Java Programming: The Object-Oriented Approach

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Next, you'll need to add an action handler to the button. Again, the basic concepts are the same—

you need to catch interesting UI events and respond to them:

import javafx.application.Application;

import javafx.event.ActionEvent;

import javafx.event.EventHandler;

import javafx.scene.Group;

import javafx.scene.Scene;

import javafx.scene.control.Button;

import javafx.scene.control.Label;

import javafx.scene.control.TextField;

import javafx.scene.layout.VBox;

import javafx.scene.text.Font;

import javafx.stage.Stage;

import javafx.geometry.Pos;

import javafx.scene.layout.HBox;

import javafx.stage.Modality;

import javafx.stage.StageStyle;

public class BMICalculatorFX extends Application {

private Stage stage;

private final TextField txtMass = new TextField();

private final TextField txtHeight = new TextField();

private final Button btnCalc = new Button("Calculate BMI");

@Override

public void start(Stage stage) throws Exception {

this.stage = stage;

VBox vbox = new VBox(10);

Label lblTitle = new Label("BMI Calculator");

lblTitle.setFont(Font.font(18));

vbox.getChildren().add(lblTitle);

vbox.getChildren().add(new Label("Your mass (kg):"));

vbox.getChildren().add(txtMass);

vbox.getChildren().add(new Label("Your height (cm):"));

vbox.getChildren().add(txtHeight);

vbox.getChildren().add(btnCalc);

btnCalc.setOnAction(new EventHandler<ActionEvent>() {

@Override

public void handle(ActionEvent ev) {

double mass;

double height;

try {

mass = Double.parseDouble(txtMass.getText());

height = Double.parseDouble(txtHeight.getText());

} catch (NumberFormatException e) {

showMessage("Check your input.", "Error in number input");

Beginning Java Programming: The Object-Oriented Approach

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