MonthViewSkin: Assigning null to a primitive. (V11.12.3)

[baumeister]

I'm getting exceptions in MonthViewSkin$MonthDayEntriesPane.update(MonthViewSkin.java:675) because the return value of a map lookup is assigned to an int even though it may be null:

Trace:

Cannot invoke "java.lang.Integer.intValue()" because the return value of "java.util.Map.get(Object)" is null
at impl.com.calendarfx.view.MonthViewSkin$MonthDayEntriesPane.update(MonthViewSkin.java:675)
at impl.com.calendarfx.view.MonthViewSkin$MonthDayEntriesPane.lambda$new$0(MonthViewSkin.java:632)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Unknown Source)

[baumeister]

Confirmed to still exist in 11.12.6.

I assume this is some sort of threading synchronization issue involving positionMap as it not always appears but can be very easily reproduced by clicking on the previous/next button in quick succession. It also happens randomly otherwise though.

Outside of analyzing the threading problem, a possible fix is to simply avoid the NPE in MonthDayEntriesPane:update, so changing

int position = positionMap.get(Objects.requireNonNull(entry.getId(), "entry ID is missing, entry type = " + entry.getClass().getName() + ", entry title = " + entry.getTitle()));
maxPosition = Math.max(maxPosition, position);

to

Integer position = positionMap.get(Objects.requireNonNull(entry.getId(), "entry ID is missing, entry type = " + entry.getClass().getName() + ", entry title = " + entry.getTitle()));
if (position!=null) 
    maxPosition = Math.max(maxPosition, position);

[baumeister]

Test case to reproduce:

import java.time.LocalDate;
import java.time.LocalTime;
import java.util.Random;
import java.util.UUID;

import com.calendarfx.model.Calendar;
import com.calendarfx.model.Calendar.Style;
import com.calendarfx.model.CalendarSource;
import com.calendarfx.model.Entry;
import com.calendarfx.view.CalendarView;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Priority;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;


public class FxCalendarTest extends Application {
	@Override
	public void start(Stage stage) {
		final VBox box = new VBox();
		final Scene scene = new Scene(box);
		stage.setScene(scene);
		Calendar calendarIncomplete = null;
		Calendar calendarComplete = null;
		CalendarView calendarView = new CalendarView();
		calendarIncomplete = new Calendar("incomplete"); 
		calendarIncomplete.setStyle(Style.STYLE2); 
		calendarComplete = new Calendar("complete"); 
		calendarComplete.setStyle(Style.STYLE1); 

		CalendarSource myCalendarSource = new CalendarSource("Calendars"); 
		calendarView.getCalendarSources().clear();
		calendarView.getCalendarSources().addAll(myCalendarSource); 
		myCalendarSource.getCalendars().clear();
		myCalendarSource.getCalendars().addAll(calendarComplete,calendarIncomplete);

		calendarView.setRequestedTime(LocalTime.now());
		calendarView.setShowPrintButton(false);
		calendarView.setShowAddCalendarButton(false);
		calendarView.setShowSearchField(false);
		calendarView.setShowSearchResultsTray(false);
		calendarView.setShowSourceTray(false);
		calendarView.setShowSourceTrayButton(false);
		calendarView.setShowPageToolBarControls(false);
		calendarComplete.setReadOnly(true);
		calendarIncomplete.setReadOnly(true);
		calendarView.setShowPageSwitcher(true);
		calendarView.setCalendarVisibility(calendarIncomplete, true);
		calendarView.setCalendarVisibility(calendarComplete, true);
		for (int i=0;i<100;i++) {
			Entry e = new Entry();
			e.setTitle(UUID.randomUUID().toString());
			e.setId(UUID.randomUUID().toString());
			e.setFullDay(true);
			e.changeStartDate(LocalDate.of(2023, randomInt(3, 11), randomInt(1,29)));
			e.changeEndDate(e.getStartDate().plusDays(randomInt(2,10)));
			e.setCalendar(randomInt(1)==0? calendarIncomplete : calendarComplete);
		}
		VBox.setVgrow(calendarView,Priority.ALWAYS);
		box.getChildren().add(calendarView);
		calendarView.showMonthPage();

		stage.show();
	}

	public static void main(String[] args) {
		launch(args);
	}
	
	static private Random randomInt = new Random(System.currentTimeMillis());
	
	public static int randomInt(int max) {
		return randomInt.nextInt(max+1);
	}

	public static int randomInt(int min,int max) {
		return randomInt.nextInt(max-min+1)+min;
	}
}

Click a couple of times on month forward and/or backward button to cause the NPE