JavaFX条形图元素上的Java 8流错误

Question

在JavaFXBarChart的getData()上使用流时，我收到以下错误

error: invalid method reference
                .map(XYChart.Series::getName);
                            ^ non-static method getName() cannot be referenced from a static context

 error: incompatible types: invalid method reference
                .map(XYChart.Series::getName);
                     ^ method getName in class Series<X,Y> cannot be applied to given types
      required: no arguments
      found: Object
      reason: actual and formal argument lists differ in length   where X,Y are type-variables:
    X extends Object declared in class Series
    Y extends Object declared in class Series

public class MainController{
        public BarChart barChart; // from fxml file
}

以下代码将成功打印条形图的类名

List<XYChart.Series> test = barChart.getData();
List<String> testList = test.stream().map(XYChart.Series::getName).collect(Collectors.toList());
System.out.println(testList);

然而，这段代码在编译时会失败

List<String> testList = barChart.getData().stream()
      .map(XYChart.Series::getName) // error line
      .collect(Collectors.toList()); 
System.out.println(testList);

为什么会抛出此错误，为什么只在第一个示例中抛出，而在后一个示例中不抛出？这两个代码示例之间的区别是什么

[使用Gradle和Java版本1.8.0_144运行]