Creating Charts in JavaFX - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 361

Next, we want to add a title to the chart, and we want to have names near the symbols in the legend node. Adding
a title to the chart is no different from adding a title to the PieChart and is achieved by the code:
scatterChart.setTitle("Speculations");
By adding a name to the three instances of XYChart.Series , we add labels to the symbols in the legend node.
The relevant part of the getChartData method becomes
Series<Integer, Double> java = new Series<>();
Series<Integer, Double> c = new Series<>();
Series<Integer, Double> cpp = new Series<>();
java.setName("java");
c.setName("C");
cpp.setName("C++");
Running the application again after applying both changes results in output similar to that shown in Figure 8-8 .
Figure 8-8. ScatterChart with a title and named symbols
Until now, we used a NumberAxis for the xAxis . Inasmuch as years can be represented as Number instances,
that works. However, because we don't do any numerical operation on the years, and because the distance between
consecutive data entries is always one year, we can also use a String value to represent this information.
We now modify the code to work with a CategoryAxis for the xAxis . Changing the xAxis from a
NumberAxis to a CategoryAxis also implies that the getChartData() method should return an instance of
ObservableList<XYChart.Series<String, Double>>a nd that implies that the different elements in a single Series
should have the type XYChart.Data<String, Double> .
In Listing 8-6, the original code has been modified to use the CategoryAxis .