Consider this:
import javafx.stage.Stage;
import javafx.scene.Scene;

/**
 * @author moonko
 */

def circle: javafx.scene.shape.Circle = javafx.scene.shape.Circle {
        radius: 25.0
    }

def toolBar: com.javafx.preview.control.ToolBar = com.javafx.preview.control.ToolBar {
        layoutX: 6.0
        layoutY: 2.0
        items: [ circle ]
}

Stage {
    title: "Toolbar Test"
    scene: Scene {
        width: 250
        height: 80
        content: [
            toolBar
        ]
    }
}

Compile, run. Nothing is shown on stage.