Docs: Added Java 8 and Jack coverage for N Preview
Change-Id: I6eaf7f5115c1d3117eefaf7cb0cbeddaa46ad437
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Adarsh Fernando
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docs/html/preview/j8-jack.jd
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docs/html/preview/j8-jack.jd
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page.title=Using Java 8 Language Features
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page.keywords="android N", "Java 8", "Jack"
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@jd:body
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<div id="qv-wrapper">
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<div id="qv">
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<h2>
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In this document
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</h2>
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<ol>
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<li>
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<a href="#supported-features">Supported Java 8 Language Features and APIs</a>
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</li>
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<li>
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<a href="#configuration">Enabling Java 8 Features and the Jack Toolchain</a>
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</li>
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</ol>
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<h2>
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See also
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</h2>
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<ol>
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<li>
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<a class="external-link" href=
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"https://source.android.com/source/jack.html">Jack (Java Android Compiler
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Kit)</a>
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</li>
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</ol>
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</div>
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</div>
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<p>
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The N Developer Preview introduces newly supported Java 8 language features
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that you can use when developing apps that target the Preview. To start using
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these features, you need to download and set up Android Studio 2.1 (preview)
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and the N Preview SDK, which include the required Jack toolchain and updated
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Android Plugin for Gradle.
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</p>
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<p>
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To learn how to set up Android Studio for the Preview, <a href=
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"{@docRoot}preview/setup-sdk.html">read the guide</a>. If you instead want to
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simply test your app's forward-compatibility, follow the guide to <a href=
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"{@docRoot}preview/run-app.html">run your app on
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the N Preview</a>.
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</p>
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<p>
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This document will discuss the new language features supported in the
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Preview, how to properly set up your project to use them, and any known
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issues you may encounter.
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</p>
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<p class="note">
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<strong>Note:</strong> Using the new Java 8 language features is not a
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requirement for developing apps that target the N Developer Preview. After
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following the set up instructions in the <a href=
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"{@docRoot}preview/setup-sdk.html">Preview guide</a>, you may use
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the Java 7 language features already supported by Android 6.0 (API level 23)
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and below.
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</p>
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<h2 id="supported-features">
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Supported Java 8 Language Features and APIs
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</h2>
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<p>
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Android does not currently support all Java 8 language features. However, the
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following features are now available when developing apps targeting the N
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Developer Preview:
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</p>
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<ul>
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<li>
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<a class="external-link" href=
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"https://docs.oracle.com/javase/tutorial/java/IandI/defaultmethods.html">Default
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and static interface methods</a>
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</li>
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<li>
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<a class="external-link" href=
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"https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html">
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Lambda expressions</a>
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</li>
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<li>
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<a class="external-link" href=
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"https://docs.oracle.com/javase/tutorial/java/annotations/repeating.html">Repeatable
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annotations</a>
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</li>
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<li>
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<a class="external-link" href=
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"https://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html">
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Method References</a>
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</li>
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<li>
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<a class="external-link" href=
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"https://docs.oracle.com/javase/tutorial/java/IandI/interfaceAsType.html">Type
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Interface</a>
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</li>
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</ul>
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<p>
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Additionally, the following Java 8 language feature APIs are now available
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with the Preview:
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</p>
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<ul>
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<li>Reflection and language-related APIs:
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</li>
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<li style="list-style: none; display: inline">
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<ul>
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<li>{@code java.lang.FunctionalInterface}
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</li>
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<li>{@code java.lang.annotation.Repeatable}
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</li>
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<li>{@code java.lang.reflect.Method.isDefault()}
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</li>
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<li>and Reflection APIs associated with repeatable annotations, such as
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{@code AnnotatedElement.getAnnotationsByType(Class)}
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</li>
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</ul>
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</li>
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<li>Utility APIs:
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</li>
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<li style="list-style: none; display: inline">
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<ul>
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<li>{@code java.util.function}
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</li>
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</ul>
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</li>
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</ul>
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<p class="note">
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<strong>Note:</strong> The N Developer Preview bases its implementation of
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lambda expressions on anonymous classes. This approach allows them to be
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backwards compatible and executable on earlier versions of Android. To test
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lambda expressions on earlier versions, remember to go to your {@code
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build.gradle} file, and set {@code compileSdkVersion} and {@code
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targetSdkVersion} to 23 or lower.
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</p>
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<h2 id="configuration">
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Enabling Java 8 Features and the Jack Toolchain
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</h2>
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<p>
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In order to use the new Java 8 language features, you need to also use the
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new <a class="external-link" href=
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"https://source.android.com/source/jack.html">Jack toolchain</a>. This new
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Android toolchain compiles Java language source into Android-readable dex
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bytecode, has its own {@code .jack} library format, and provides most tool chain
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features as part of a single tool: repackaging, shrinking, obfuscation and
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multidex.
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</p>
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<p>Here we compare the two toolchains used to build Android DEX files:</p>
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<ul>
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<li>Legacy: javac ({@code .java} > {@code .class}) > dx ({@code
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.class} > {@code .dex})
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</li>
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<li>Modern: Jack ({@code .java} > {@code .jack} > {@code .dex})
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</li>
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</ul>
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<h3>
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Configuring Gradle
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</h3>
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<p>
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To enable the Java 8 language features and Jack for your project, enter the
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following in your module-specific {@code build.gradle} file:
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</p>
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<pre>
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android {
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...
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defaultConfig {
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...
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jackOptions {
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enabled true
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}
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}
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compileOptions {
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sourceCompatibility JavaVersion.VERSION_1_8
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targetCompatibility JavaVersion.VERSION_1_8
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}
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}
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</pre>
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<h3>
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Known Issues
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</h3>
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<p>
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Instant Run, introduced in Android Studio 2.0 (Beta), does not currently work
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with Jack and will be disabled while using the new toolchain.
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</p>
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<p>
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Since Jack does not generate intermediate class files when compiling an app,
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tools that depend on these files do not currently work with Jack. Some examples of
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these tools are:
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</p>
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<ul>
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<li>Lint detectors that operate on class files
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</li>
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<li>Tools and libraries that require the app’s class files (e.g. JaCoCo and Mockito)
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</li>
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</ul>
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If you find other problems while using Jack, <a class="external-link" href=
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"http://tools.android.com/filing-bugs">please report bugs</a>.
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