import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.stage.Stage;

public class StageSizeTest extends Application {
    @Override
    public void start(final Stage primaryStage) {
        final Scene scene = new Scene(new Label("test"));
        primaryStage.setScene(scene);
        primaryStage.sizeToScene();
        primaryStage.setWidth(1000);
        primaryStage.setHeight(1000);
        primaryStage.show();
        System.out.println(primaryStage.getWidth());
        System.out.println(primaryStage.getHeight());
    }
}