Introduction
Skateboarding is an exciting sport that requires good equipment for an enjoyable experience. Skateboard Designer is a JavaFX application designed to help users select skateboard parts and compute the cost. This article will discuss the critical parts of the code that make this application work.
About the Code
The Skateboard Designer has four categories of products: Decks, Truck Assemblies, Wheels, and Miscellaneous items. Each category is represented by a Java Map that stores the product name as the key and the product price as the value. These Maps are static and are initialized using the static block. It ensures that the Maps are loaded when the class is loaded into the memory, and they are ready for use by other parts of the application.
private static final Map<String, Double> DECKS = new HashMap<>();
private static final Map<String, Double> TRUCK_ASSEMBLIES = new HashMap<>();
private static final Map<String, Double> WHEELS = new HashMap<>();
private static final Map<String, Double> MISC_ITEMS = new HashMap<>();The UI of the application is created in the start() method. The method creates four HBox and VBox containers to hold the ComboBoxes, ListView, and the Labels for the sub-total, tax, and total values. The ComboBoxes are created using the ComboBox class, and the ListView is created using the ListView class. The SelectionMode property of the ListView is set to MULTIPLE to allow the user to select multiple items.
....
Label misc = new Label("Miscellaneous");
ListView<String> miscListView = new ListView<>(FXCollections.observableArrayList(MISC_ITEMS.keySet())); miscListView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);The Bindings class in the javafx.beans.binding package is used to compute the sub-total, tax, and total values based on the selected items in the ComboBoxes and the ListView. The createDoubleBinding() method is used to create a DoubleBinding that computes the sub-total value based on the selected items. The multiply() and add() methods are used to compute the tax and total values, respectively. The Bindings.format() method is used to format the text of the sub-total, tax, and total Labels.
DoubleBinding subtotal = Bindings.createDoubleBinding(() ->
{
double deckPrice = DECKS.getOrDefault(deckComboBox.getValue(), 0.0);
double truckPrice = TRUCK_ASSEMBLIES.getOrDefault(truckComboBox.getValue(), 0.0);
double wheelsPrice = WHEELS.getOrDefault(wheelsComboBox.getValue(), 0.0);
return deckPrice + truckPrice + wheelsPrice + miscListView.getSelectionModel().getSelectedItems().stream()
.mapToDouble(MISC_ITEMS::get)
.sum();
}, deckComboBox.valueProperty(), truckComboBox.valueProperty(), wheelsComboBox.valueProperty(), miscListView.getSelectionModel().getSelectedItems());
DoubleBinding tax = Bindings.multiply(0.07, subtotal);
DoubleBinding total = (DoubleBinding) Bindings.add(subtotal, tax);
subTotalLabel.textProperty().bind(Bindings.format("Subtotal: $%.2f", subtotal));
taxLabel.textProperty().bind(Bindings.format("Tax (7%%): $%.2f", tax));
totalLabel.textProperty().bind(Bindings.format("Total: $%.2f", total));Why Use Bindings?
Bindings are a powerful feature in JavaFX that allow you to create a live link between the value of a property and the value of an expression. This means that when the value of property changes, the expression that depends on that property is automatically updated. Bindings are useful for creating reactive user interfaces, where changes made to one part of the interface automatically update other parts of the interface.
For example, instead of manually updating the text of a label every time a related value changes, you can use a binding to automatically update the label when the value changes. This can make the code easier to understand and less error-prone.
In addition, bindings can also improve performance by reducing the amount of unnecessary computation. By using bindings to only update the UI when necessary, you can avoid unnecessary updates and improve the responsiveness of your application.
The purpose of using bindings in this code is to provide a convenient way to keep track of the cost of all the different components that the user selects for their skateboard. Instead of manually calculating the total cost every time a component is added or removed, we can use bindings to automatically update the cost whenever any of the component selection changes.
The code creates three DoubleBindings – subtotal, tax, and total – and binds them to the values of different components selected by the user, using the createDoubleBinding() and multiply() methods from the Bindings class. The sub-total is calculated by adding up the cost of the deck, truck assembly, wheels, and any miscellaneous items that are selected. The tax is then calculated as 7% of the sub-total, and the total is calculated by adding the sub-total and tax.
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Challenges
When using bindings, it can be difficult to track exactly how the values are being updated, especially when there are multiple bindings involved. Bindings create a dynamic relationship between values, and any changes made to one value can impact the others. This can make it challenging to understand the precise cause and effect of changes to values.
Debugging can also be tricky when using bindings, especially if there are complex calculations involved. If a bug is introduced in the code that affects the binding, it can be difficult to isolate and fix the problem. It can also be challenging to debug binding-related issues that arise due to interactions between different parts of the code.
Another challenge of using bindings is ensuring that they are set up correctly. Bindings can be difficult to configure correctly, and if they are not set up correctly, they can lead to unexpected behavior or errors at runtime. For example, if a binding is created incorrectly, it may cause an infinite loop or prevent the values from updating correctly.
Conclusion
It’s worth noting that bindings can be particularly useful when dealing with complex UIs that require frequent updates based on user input. By binding UI components to underlying data models, developers can create dynamic and responsive applications that are easy for users to interact with.
However, as with any tool, it’s important to use bindings judiciously and consider the potential downsides, such as debugging difficulties and unexpected behavior. Before implementing bindings, developers should carefully consider the specific requirements of their application and weigh the benefits and drawbacks.
The Skateboard Designer application provides a practical example of how to use bindings effectively in a real-world application. By using Maps to store product information and ComboBoxes and ListView to allow users to select items, the application creates a dynamic and user-friendly UI that responds to user input in real-time.
Overall, the Skateboard Designer application is a great example of how to use JavaFX and the javafx.beans.binding package to create dynamic and responsive UIs. By carefully considering the use of bindings and using them judiciously, developers can create applications that are both performant and user-friendly.
Reference
T. Gaddis and G. Muganda, Starting Out with Java – From Control Structures through Data Structures, 4th Edition, 330 Hudson Street, NY NY 10013: Pearson, 2019.
