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Kiwi Utilities Library

Kiwi is a small set of utilities inspired by Guava.

Why the fruity name? Well, I like kiwis and guava is a fruit after all. That, and I didn't want to create 100th gdx-util(s) out there, to be honest.

Since LibGDX is using its own collections - without implementation of standard Java interfaces, for better and for worse - most Java collection utilities are somewhat useless. Or they are unavailable for GWT and/or contain a lot of unnecessary classes, which are pretty easy to mix up and import by mistake. Kiwi tries to change that, by having LibGDX-based utilities that could be at least partially useful in pretty much any GDX application.

This library aims to provide what is missing, while NOT trying to replace what you can already have. A third implementation of Optional (Guava, Java 8) would be redundant and unnecessary, for example. That's why most classes try to avoid name (and functionality) collisions with original Java utilities and Guava library - no point in reinventing the wheel or creating confusion.


The one package that kind of goes against what I've just said. Yeah.

  • Comparables: not as powerful as Guava, but it will save you some magic numbers in conditions.
  • Exceptions: utilities for management of exceptions.
  • Nullables: utilities for objects that might be null, mostly because Java 6 is missing official Objects utility. Again, you will probably be better off using optionals, but sometimes we do have to deal with unpleasant external APIs.
  • Strings: since Scene2D widgets often make use of custom StringBuilder class and might actually expect or return CharSequences from time to time, this class provides static utility methods consuming (mostly) CharSequence instances. They are still useful for regular strings, of course.
  • TimeUtilities: time conversion methods. Might be helpful for LibGDX timers and actions.


Ever wanted to refactor and split a method, but you needed to return at least two objects at once to make it work? Did you wonder why Java has generic utilities for collections, but misses these simple object containers? Well, you don't have to worry about that using Kiwi, as some simple immutable and mutable pairs and triples implementations are provided.

  • Tuple: interface of all tuples. Ensures that tuples are serializable and iterable, additionally to providing array-like access by index and utility methods (like contains).
  • DoupleTuple, TripleTuple: these two extend the basic interface, providing additional access methods.
  • Pair, Triple: immutable tuples. Use where possible.
  • MutablePair, MutableTriple: as you can guess, mutable tuples. Use when necessary.
  • SingleTuple: interface for a tuple wrapping around a single object.
  • Single, MutableSingle: immutable and mutable single object wrappers. Useful when you need to pass a single object as an iterable.

All tuple implementation classes contain static factory methods to avoid awkward Java 6 generics syntax.


These packages depend on LibGDX and are the core of this library.

  • GdxUtilities: generic application utilities that were hard to classify. If you're sick of manually glClearing, putting screen width and height/input data into vector or checking if application has the correct platform type, you will like this class.
  • AbstractApplicationListener: ApplicationAdapter replacement with render implementation that will clear the screen with black color and call abstract render(float deltaTime) method that you're forced to override (which any sensible graphical application should do anyway). Aims to reduce boilerplate code a little and let you focus on the game logic rather than OpenGL calls.
  • InputAwareApplicationAdapter: combines ApplicationAdapter and InputAdapter: implements ApplicationListener and InputProcessor with empty methods. Allows to easily set up application listeners that also listen to user input.
  • InputAwareApplicationListener: updated version of InputAwareApplicationAdapter. Similarly to AbstractApplicationListener, automatically clears the screen and calls render(float deltaTime). create() method invokes initiate() (where you should move your application creation code) and then sets this listener as application's main InputProcessor for extra utility.


  • Disposables: static utility methods for disposable objects. No more manual iterating over resources or null checks before disposing - this is all handled for you. Note that some objects might throw exceptions when disposing multiple times (or for whatever reason) and some silencing disposing methods are also provided if you really don't care why the exceptions are thrown.
  • StatefulDisposable: extends Disposable interface with a utility check method isDisposed().
  • Asset: a utility interface for an enum containing multiple assets. A sample implementation is provided - AbstractInternalAsset (although it is advised to be copied and used by an enum, since enums cannot extend).


Hate null checks while creating lazy variables? Good, so do I. While such objects might be much easier to use with Java 8 (where you can create a provider/supplier with a simple lambda), I think it's still much more acceptable than having a bunch of ifs and non-final variables, where they actually could be final.

  • Lazy: basic class of a lazy variable wrapper. Allows to create a final reference to a wrapped, lazy object that will be initiated (or assigned) on the first get() call thanks to the passed provider object. This class also contains static utility factory methods. If you really don't want to use providers, but do need a base implementation, extend this class (giving it a type you need), pass null to super constructor and override getObjectInstance() method to provide your own object creation implementation.
  • DisposableLazy: extends Lazy; wraps around a disposable object and implements Disposable interface for additional utility.
  • ConcurrentLazy: extends Lazy; safe to use by multiple threads.
  • DisposableConcurrentLazy: extends DisposableLazy; safe to use by multiple threads.

Utility classes for lazy objects. Create - or give access to, depending on implementation - an instance of a object on each call.

  • ObjectProvider: functional interface with one, no-parameter method - provide. Implementation of this interface is often required by lazy objects and allows to initiate an object as soon as its needed, rather than at once.
  • ReflectionObjectProvider: an implementation of ObjectProvider that uses reflection to construct objects with public, no-argument constructors. Note that the objects have to be reflected and this implementation might not be the best choice if the provider is used very often (for example, when it comes to lazy collections). Works on GWT, but you do have to include used classes for reflection.
  • ArrayObjectProvider, MapObjectProvider, SetObjectProvider: stateless implementations of ObjectProvider interface that do not use reflection. They allow to create LibGDX collections.
  • SingletonProvider: wraps around a single object, returning it on each provide() call. Utility for creating local singletons.


LibGDX collections utilities. To avoid collisions with Guava and Java API, these classes start with Gdx.

  • GdxArrays: utilities for LibGDX array collections. Includes array type conversions, common operations, null-safe checks and factory methods.
  • GdxLists: utilities for LibGDX list collections: PooledLinkedList and SortedIntList. Includes factory methods, null-safe utilities and custom, reusable PooledLinkedList iterators (since it does not implement Iterable interface).
  • GdxMaps: utilities for LibGDX maps. Conversions are limited since there is no map interface in LibGDX, but it should be enough for most needs.
  • GdxSets: utilities for LibGDX sets. Not as powerful as Guava, but you do get union and intersect.

Since disposable and immutable collections provide all static factory methods, these are not included in GdxCollections utilities.


Utilities for holding multiple assets. On dispose() call, these collections dispose of all their children that are not null.

  • DisposableArray: Array extension implementing Disposable interface.
  • DisposableObjectMap: ObjectMap extension implementing Disposable interface.
  • DisposableObjectSet: ObjectSet extension implementing Disposable interface.

All of these classes come with static factory methods.


Semi-immutable collections extending most common LibGDX containers. Due to original API, true immutability was not fully possible.

  • ImmutableArray: Array extension with overshadowed public variables, iterators with blocked remove() method and overridden modifying operations. Still mutable when casted to an Array and accessing public variables (items, size) - but as long as only methods are used, you're safe.
  • ImmutableObjectMap: ObjectMap extension with overshadowed public variables and overridden modifying operations. Mutable through iterators (which accessed private variables and could not have been easily reproduced) or casting to ObjectMap and accessing size variable. As long as you use public methods and standard for-each loops, you're safe.
  • ImmutableObjectSet: ObjectSet extension with overshadowed public variables and overridden modifying operations. Mutable through iterators (which accessed private variables and could not have been easily reproduced) or casting to ObjectSet and accessing size variable. As long as you used public methods and standard for-each loops, you're safe.

All of these classes come with static factory methods.


Similarly to Lazy utility containers, lazy collections create objects as soon as they are needed using ObjectProviders. Especially useful for collections of collections.

  • LazyArray: creates objects on get(int index) if the value associated with the index is null. Never throws out of bounds exception for reasonable indexes (non-negative).
  • LazyObjectMap: creates objects on get(Object key) if the key is not present in the map. Never returns null if its provider is properly implemented.


  • PooledList: PooledLinkedList done right. This is a LinkedList equivalent that pools its nodes and caches its iterator (limiting GC). As opposed to PooledLinkedList, this implementation allows to share a common node pool across multiple list instances and implements Iterable (which is more than desired for collections).


  • Preference: utility interface for common preference operations. Advised to be implemented by an enum to provide static access to each of application's preferences. Comes with an example implementation - PreferenceWrapper.
  • ApplicationPreferences: utility container for application's preferences. Manages a map of cached preferences to avoid reading preferences multiple times and ensure that the returned Preferences object for the given path is always the same and in sync.


  • Reflection: class with static utilities that make LibGDX reflection a bit less awkward to use.
  • Annotations: utilities for annotation processing.


  • Actors: simple, common utility methods for Scene2D actors.
  • Alignment: wraps around Align class to provide human-(instantly-)readable alignment checking methods.
  • Padding: utility container for paddings and spacings. Makes it easier to keep static padding settings, without having to create multiple variables.
  • InterfaceSkin: utility container that provides static access to UI skin.
  • Tooltips: simple utilities for the new LibGDX official tooltips.


When you cannot or don't want to use actions or tweening utilities.

  • ColorRange: utility for simple color transitions.
  • FloatRange: utility for simple float number transitions. Might be useful for color's alpha.


  • LetterboxingViewport: combination of ScreenViewport and FitViewport, which changes its world size on screen resize and attempts to keep chosen aspect ratio by applying letterboxing. Honors screen density (pixel per inch ratio) and should look acceptable on both desktop and mobile devices. Very convenient for GUIs, as it will not unnecessarily scale the assets when resized.
  • Viewports: static utilities for working with LibGDX viewports.


LibGDX does provide logging utilities with Application methods and simple com.badlogic.gdx.utils.Logger class, but they both lack arguments support and features we might know from standard loggers, like including class name and current time. Kiwi loggers are slightly more complex, while trying to add as little overhead as possible. Typical usage examples:


        // Turning off debug logging:
        // Turning on info logging:;
        // Turning on error logging:
        // Completely turning off logging:
        // Note that all levels are turned on by default.

        // Including current time in logs:
        // Using asynchronous loggers (not advised unless justified):
        // Using simple class names instead of full names:

Obtaining a logger:

        private static final Logger LOGGER = LoggerService.forClass(MyClass.class);
        // Non-static logger reference, very convenient in abstract classes:
        protected final Logger logger = LoggerService.forClass(getClass());
        // Note that loggers are cached; if you try to obtain multiple loggers
        // for the same class, the same instance will be returned each time.


        try {
          logger.debug("Logging a debug message!");
"Logging an info message with some params: {0}, {1}, {2}.", someVar, 5, someOtherVar);
        } catch (Exception exception) {
          logger.error(exception, "Exception!");
          logger.debug(exception, "Exception thrown, some extra data: {0} and {1}.", someVar, someOtherVar);
        // Exception as the first argument is a design choice; otherwise var-args of
        // logging arguments could not be used.

Example logs:

        logger.debug("Some message.");
        // [DEBUG] com.github.czyzby.ExampleClass: Some message.

        LoggerService.logTime(true);"Kiwi is {0}.", "useful");
        // [INFO]  com.github.czyzby.ExampleClass (Mon Nov 02 14:21:31 CET 2015): Kiwi is useful.

        logger.error(new RuntimeException("Example."), "Exception thrown!");
        // [ERROR] com.github.czyzby.ExampleClass (Mon Nov 02 14:21:31 CET 2015): Exception thrown!
        // java.lang.RuntimeException: Example.
        //   at --stack goes here--

Loggers delegate logging calls to current Application instance, so they should work on every platform.


gdx-kiwi is available through the official project creator tool: gdx-setup (in third party extensions). However, its version might not be up to date.

Core project Gradle dependency:

        compile "com.github.czyzby:gdx-kiwi:$libVersion.$gdxVersion"

$libVersion is the current version of the library, usually following MAJOR.MINOR schema. $gdxVersion is the LibGDX version used to build (and required by) the library. You can check the current library version here - or you can use the snapshots.

GWT module:

        <inherits name="" />