Creating Charts in JavaFX - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 357

index for Java, C, and C++ in 2011, and add random values (between -2 and +2) to them for each year until 2020. The
resulting (year, number) pairs for Java constitute the Java Series, and the same holds for C and C++. As a result,
we have three series, each containing 10 pairs.
A major difference between a PieChart and an XYChart is the presence of an x axis and a y axis in the XYChart .
These axes are required when creating an XYChart , as can be observed from the following constructor.

XYChart (Axis<X> xAxis, Axis<Y> yAxis)

The Axis class is an abstract class extending Region (hence also extending Parent and Node ) with two subclasses:
CategoryAxis and ValueAxis . The CategoryAxis is used to render labels that are in the String format, as can be
observed from the class definition:

public class CategoryAxis extends Axis<java.lang.String>

The ValueAxis is used to render data entries that represent a Number . It is an abstract class itself, defined as follows.

public abstract class ValueAxis <T extends java.lang.Number> extends Axis<T>

The ValueAxis class has one concrete subclass, which is the NumberAxis :

public final class NumberAxis extends ValueAxis<java.lang.Number>

The differences between those Axis classes will become clear throughout the examples. We now show some
examples of the different XYChart implementations, starting with the ScatterChart . Some features common to all
XYChart s are also explained in the section on ScatterChart .

■ Because the Axis classes extend Region , they allow for applying the same Css elements as any other
Regions . this allows for highly customized Axis instances.

Note

Using the ScatterChart
An instance of the ScatterChart class is used to render data where each data item is represented as a symbol in a
two-dimensional area. As mentioned in the previous section, we will render a chart containing three series of data,
representing the hypothetical evolution of the TIOBE index for Java, C, and C++. We first show the code of a naive
implementation, and refine that to something more useful.

A Simple Implementation
A first implementation of our application using a ScatterChart is shown in Listing 8-5.

Listing 8-5. First Implementation of Rendering Data in a ScatterChart

package projavafx ;

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;