Is it possible to use Java 8 for Android development?

При поиске в Интернете неясно, поддерживается ли Java 8 для разработки под Android или нет.

Прежде чем я загружу / настрою Java 8, может ли кто-нибудь указать мне на какую-либо "официальную" документацию, в которой говорится, поддерживается Java 8 для разработки под Android или нет.

ОБНОВЛЕНИЕ 2017/11/04 - Android Studio 3.0 теперь имеет встроенную поддержку Java 8. gradle-retrolambda теперь она больше не нужна. Посмотреть https://developer.android.com/studio/write/java8-support.html

Приведенная выше ссылка также содержит инструкции по миграции, если вы используете gradle-retrolambda. Оригинальный ответ ниже:

Android не поддерживает Java 8. Он поддерживает только до Java 7 (если у вас есть kitkat) и по-прежнему не имеет invokedynamic, только новый синтаксический сахар.

Если вы хотите использовать лямбды, одну из основных функций Java 8 в Android, вы можете использовать gradle-retrolamba. Это зависимость сборки gradle, которая интегрирует retrolambda, инструмент, который преобразует байт-код Java 8 обратно в Java 6/7. В принципе, если вы настроите компилятор в Android Studio на компиляцию байт-кода Java 8, тем самым разрешив лямбды, он преобразует его обратно в байт-код Java 6/7, который затем, в свою очередь, преобразуется в байт-код dalvik. Это хак на случай, если вы хотите опробовать некоторые функции JDK 8 в Android вместо официальной поддержки.

java 8

Android поддерживает все функции языка Java 7 и подмножество функций языка Java 8, которые зависят от версии платформы.

Чтобы проверить, какие функции Java 8 поддерживаются

Используйте функции языка Java 8

Мы решили добавить поддержку функций языка Java 8 непосредственно в текущий набор инструментов javac и dx и отказаться от набора инструментов Jack. В этом новом направлении существующие инструменты и плагины, зависящие от формата файла класса Java, должны продолжать работать. В дальнейшем возможности языка Java 8 будут изначально поддерживаться системой сборки Android. Мы планируем запустить это как часть Android Studio в ближайшие недели, и мы хотели как можно раньше поделиться с вами этим решением.

Будущее поддержки языковых функций Java 8 на Android

Пользователи Eclipse:

Для старых разработчиков, предпочитающих Eclipse, Google прекращает поддержку Eclipse Android Developer tools

если вы установили Java 8 JDK, то попробуйте, если возникнут какие-либо проблемы, попробуйте установить компилятор как 1.6 в Eclipse из меню window → Настройки → Java → Компилятор. Java 7 тоже будет работать:

Java 7 or higher is required if you are targeting Android 5.0 and
higher.

install multiple JDK and try.

You can indeed use gradle-retrolamba gradle build dependency to use Java 8 for Android Development.

Below is the complete guide that I have recently followed to run lambda expressions for Android development. The original source of this guide is mentioned at the end.

In this guide, a method for bringing some Java 8 features into
Android Development Tools will be demonstrated, specifically aiming at
Eclipse IDE. However, steps which will be described throughout this guide might also be adapted to Google’s new uprising development
environment, Android Studio. It is based on the community edition of
popular IntelliJ Idea IDE by JetBrains and it has recently been
upgraded to its ‘beta’ version by Google in early July 2014, slightly
before this guide was written. Eclipse will remain as the prominent
development environment, at least for a while, and considering the
fact that most Android projects have been developed using Eclipse, a
method for bringing new Java 8 features like lambda expressions into
ADT seems to be quite useful for developers.

Android Development is based on a custom Java implementation called
Apache Harmony Project which was terminated back in 2011. The most
commonly used Java syntax in Android Development is Java 6 (v1.6) and
Java 7 (v1.7) is also partially supported on the KitKat edition
(Android 4.4.+). Therefore, Java 8 features like lambda expressions
cannot be used directly in the Android App Development without
applying some tweaks into the development tools. Luckily, these
constructs are basically some ‘syntactic sugar’ enhancements which
give developers the shortcomings of things like ‘anonymous classes’
and they can be translated into Java 6 or Java 7 classes.

A recent approach for translating a Java 8 source code into lower Java
versions is called RetroLambda. This library makes developers run
Java 8 code with lambda expressions on Java 7 or even lower.
Unfortunately, Java 8 features other than lambda expressions are not
supported by RetroLambda for now but the concept of lambda expressions
is the biggest leap on Java 8 platform and it’s a great tool for
Android developers anyway.

Details about this library can be found on its GitHub page:

https://github.com/orfjackal/retrolambda#getting-started

Also, a Gradle plugin for RetroLambda created by another developer
allows Gradle-based builds to be implemented in Java or Android
Projects. However, the developer only mentions about integrating this
plugin into Android Studio environment. Details can be found on its
GitHub page:

https://github.com/evant/gradle-retrolambda

Using these infrastructures within an Eclipse-based development
environment cannot be approached directly but it’s doable and will be
demonstrated throughout this guide.

Preparation

This guide assumes that the reader has a basic understanding of Android Development and it is based on ADT version 22.6.2 because recent ADT version 23.0.2 seems to have problems like layout folder creation. Details about this issue can be found under the following link:

http://code.google.com/p/android/issues/detail?id=72591

Steps in this guide will be given for a Windows 8.1 64-bit development machine but they can easily be adapted to other platforms. The new build system Gradle will be used for build/clean processes and its installation procedure will also be provided. Also, both JDK 8 and JDK 7 must coexist on the development machine. Steps given below must be followed to install them:

• Go to JDK 8 early access preview page http://jdk8.java.net


• Download JDK 8u20 and install it. JRE 8 installation is not necessary and it can be skipped


• Go to JDK 7 latest stable release page http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html


• Download JDK 7u65 and install it. JRE 7 installation is again not necessary and it can be skipped


• Add JDK 8 home folder and JDK 8 bin folder to your %PATH% variable


• Create a new environment variable JAVA_HOME with the value of the path of JDK 8 home folder


• Create a new environment variable JAVA8_HOME again with the value of the path of JDK 8 home folder


• Create a new environment variable JAVA7_HOME with the value of the path of JDK 7 home folder


• Open a terminal window and run java -version command and verify that Java 8 is up and running


• Run javac -version command in the same window and verify that JDK 8 Java compiler is also up and running

Now, ADT-22.6.2 must be downloaded from the following link:

http://dl.google.com/android/adt/22.6.2/adt-bundle-windows-x86_64-20140321.zip

• Download ADT and unzip its contents into a folder, e.g. D:\adt


• Define a new environment variable called ANDROID_HOME with the value of the path of your ADT installation folder, e.g. D:\adt\sdk


• Add your Android SDK Platform Tools and Android SDK Tools folders, e.g. D:\adt\sdk\tools and D:\adt\sdk\platform-tools, to your %PATH% variable


• Create a shortcut to Eclipse IDE if you like. It is located under your ADT installation folder, e.g. D:\adt\eclipse


• Run Eclipse IDE and create a workspace, e.g. D:\adt\workspace


• Click on the Android SDK Manager button which is located on the toolbar


• Select Android SDK Build tools Rev. 19.1 and Android Support Library only. Un-select everything else and install these two packages.

If everything goes well, ADT will be up and running.

The installation of the following tools is also highly recommended:

• Eclipse Kepler Java 8 Support: It makes Eclipse recognize new Java 8 syntax extensions and makes you get rid of annoying red dots in your Java code editor. It might be installed through Help -> Install New Software in Eclipse. Enter http://download.eclipse.org/eclipse/updates/4.3-P-builds/ into the Work with field and continue to install it.

  
  



• Nodeclipse/Enide Gradle: It is mainly used to highlight Groovy language keywords. Groovy is used as the DSL for Gradle build scripts. This plugin can be installed through Eclipse Marketplace. However, Eclipse within ADT-22.6.2 does not come along with Eclipse Marketplace Client. Therefore, you will first need to install Eclipse Marketplace Client by means of Install New Software tool in Eclipse. Enter http//:download.eclipse.org/mpc/kepler/ into the Work with field and continue to install it. After installing Eclipse Marketplace Client, you may search for Nodeclipse/Enide Gradle in the Eclipse Marketplace Client and install it.

  
  



• Genymotion Virtual Device: It is a great replacement of the default Android Virtual Device which comes along with ADT. AVD is annoyingly cumbersome and it keeps on crashing for no reason. Genymotion makes you prepare Android VD's using CyanogenMod images which are executed by Oracle VirtualBox. Its single user license is for free and it can be downloaded from http://www.genymotion.com. Only a login is required and it can also be integrated into Eclipse. Details can be found under:

  
  

https://cloud.genymotion.com/page/doc/#collapse8

Below is a screenshot of an Android 4.3 based CyanogenMod virtual device,

It might be considered as a fully-fledge Android device running on a x86 or x64 based personal computer. In order to use Google services like Google PlayStore on this virtual device, a gapps image for the Android version that it uses must be flashed onto the device. A proper gapps image for the device might be downloaded from CyanogenMod website:

http://wiki.cyanogenmod.org/w/Google_Apps

Gradle installation is optional since it is also provided by Android SDK itself but its separate installation is highly recommended. Installation of it might be conducted by following these steps:

• Go to Gradle web site: http://www.gradle.org/

  
  



• Click Downloads

  
  



• Under Previous Releases choose version 1.10 and download either gradle-1.10-all.zip or gradle-1.10-bin.zip

  
  



• Unzip its contents into a folder, e.g. D:\adt\gradle

  
  



• Define a new environment variable called GRADLE_HOME with the value of the path of your Gradle installation folder, e.g. D:\adt\gradle

  
  



• Add your Gradle binaries folder, e.g. D:\adt\gradle\bin, to your %PATH% variable

  
  



• Open a terminal window and run gradle -v command and verify that it`s up and running
  If you have come up to this point successfully then it means that you are ready to create your first Android App using Java 8 features.

  
  

Demo App

A simple app will be created to demonstrate the usage of the tools which were described in the previous section.
You may simply follow the steps given below to get an insight on using lambda expressions in Android Developer Tools:

• Run Eclipse IDE and create a new Android App by selecting File -> New -> Other -> Android -> Android Application Project


• Fill in the form that comes up as shown below:

• Simply click the Next button on the following forms and click the Finish button on the last one. Wait till ADT finishes loading up the project

  
  



• Right-click on the project and select New -> Folder and name it builders

  
  



• Right-click on the gen (Generated Java Files) folder and delete it. Gradle will generate the same files for us soon and we will add them into the projects build path. The gen` folder created by the default Ant builder is no longer needed and the artifacts under that folder will be obsolete

  
  



• Create following batch files under the builders folder:

  
  

  - gradle_build.cmd
  - gradle_post_build.cmd
  - gradle_clean.cmd
  

  
  



• Fill in these batch files as follows:

  
  

gradle_build.cmd:

gradle_post_build.cmd:

gradle_clean.cmd:

• Un-select Project -> Build Automatically menu option


• Right-click on the project and select Properties -> Builders and un-select all default builders provided by ADT


• Click the New button in the same window and select Program and click OK


• New builder configuration window will appear. Fill in its tabs as follows:

Main Tab of the new Builder Configuration

Refresh Tab of the new Builder Configuration

Environment Tab of the new Builder Configuration

Build Options Tab of the new Builder Configuration

• Create the second builder called Gradle_Post_Build that uses gradle_post_build.cmd as its program. All other settings of this builder must exactly be the same with the previously created builder. This builder will be responsible for copying the artifacts created by the build process into the bin folder.


• Create the third builder called Gradle_Cleaner that uses gradle_clean.cmd as its program. Only Run the builder setting in the final tab must be set as During a Clean. All other settings of this builder must exactly be the same with the first builder. This builder will be responsible for cleaning the artifacts created by the build process as the name suggests.

New Builders of the HelloLambda Project

• Right-click on the project and select Export


• Select Android -> Generate Gradle Build Files and click Next


• Select the project in the next window and click Finish


• Go to your project's root folder and delete the files gradlew and gradlew.bat. Also delete gradle folder


• Switch back to Eclipse and select Project -> Clean menu option. Fill in the form that shows up as follows:

Clean Project Window

• Click OK and wait till the cleaning process completes


• Add the Java code snippet given below right after the call to setContentView function in your MainActivity class:

• Change the beginning of the build.gradle file till the sourceCompatibility section as follows:

• Right-click on the project and select Properties -> Java Compiler option and set all compliance levels to Java 8. This will make Eclipse recognize new Java 8 constructs like lambda expressions.


• Click No in the notification window


• Right-click on the project and select Build project. Eclipse will start building the project.

Build Process

• Right-click on the project and go to Properties -> Java Build Path. Add the following folders to the build path (also shown in below image):

  
  
  
  
  • build\source\buildConfig\debug
  
  
  • build\source\r\debug
  
  
  
  

Eclipse will now be able to recognize R.java and buildConfig.java files and it will not display any red dots which denote errors related to the resource files of the project.

• Create a new Run Configuration for your Android target platform by right-clicking on the project and then selecting Run As -> Run Configurations. For instance, this demo application looks like shown below on the Genymotion VD:

HelloLambda Application

You may observe in the LogCat window that the code snippet with a simple lambda expression works properly

Source: Using Java 8 Lambda Expressions in Android Developer Tools

Follow this link for new updates. Use Java 8 language features

Old Answer

As of Android N preview release Android support limited features of Java 8 see Java 8 Language Features

To start using these features, you need to download and set up Android
Studio 2.1 and the Android N Preview SDK, which includes the
required Jack toolchain and updated Android Plugin for Gradle. If you
haven't yet installed the Android N Preview SDK, see Set Up to Develop
for Android N.

Supported Java 8 Language Features and APIs

Android does not currently support all Java 8 language features.
However, the following features are now available when developing apps
targeting the Android N Preview:

Default and static interface methods

Lambda expressions (also available on API level 23 and lower)

Repeatable annotations

Method References (also available on API level 23 and lower)

There are some additional Java 8 features which Android support, you can see complete detail from Java 8 Language Features

Update

Note: The Android N bases its implementation of lambda expressions on
anonymous classes. This approach allows them to be backwards
compatible and executable on earlier versions of Android. To test
lambda expressions on earlier versions, remember to go to your
build.gradle file, and set compileSdkVersion and targetSdkVersion to
23 or lower.

Update 2

Now Android studio 3.0 stable release support Java 8 libraries and Java 8 language features (without the Jack compiler).