Information in Android Studio Flamingo



Posted by Clément Béra, Senior software program engineer

Information are a brand new Java characteristic for immutable knowledge service lessons launched in Java 16 and Android 14. To make use of information in Android Studio Flamingo, you want an Android 14 (API degree 34) SDK so the java.lang.Report class is in android.jar. That is obtainable from the “Android UpsideDownCake Preview” SDK revision 4. Information are basically lessons with immutable properties and implicit hashCode, equals, and toString strategies primarily based on the underlying knowledge fields. In that respect they’re similar to Kotlin knowledge lessons. To declare a Individual document with the fields String title and int age to be compiled to a Java document, use the next code:

@JvmRecord
knowledge class Individual(val title: String, val age: Int)

The construct.gradle file additionally must be prolonged to make use of the proper SDK and Java supply and goal. At the moment the Android UpsideDownCake Preview is required, however when the Android 14 remaining SDK is launched use “compileSdk 34” and “targetSdk 34” instead of the preview model.

android {
compileSdkPreview "UpsideDownCake"

defaultConfig {
targetSdkPreview "UpsideDownCake"
}

compileOptions {
sourceCompatibility JavaVersion.VERSION_17
targetCompatibility JavaVersion.VERSION_17
}
kotlinOptions {
jvmTarget = '17'
}
}

Information don’t essentially convey worth in comparison with knowledge lessons in pure Kotlin packages, however they let Kotlin packages work together with Java libraries whose APIs embody information. For Java programmers this enables Java code to make use of information. Use the next code to declare the identical document in Java:

public document Individual(String title, int age) {}

Apart from the document flags and attributes, the document Individual is roughly equal to the next class described utilizing Kotlin supply:

class PersonEquivalent(val title: String, val age: Int) {

override enjoyable hashCode() : Int {
return 31
* (31 * PersonEquivalent::class.hashCode()
+ title.hashCode())
+ Integer.hashCode(age)
}

override enjoyable equals(different: Any?) : Boolean {
if (different == null || different !is PersonEquivalent) {
return false
}
return title == different.title && age == different.age
}

override enjoyable toString() : String {
return String.format(
PersonEquivalent::class.java.simpleName + "[name=%s, age=%s]",
title,
age.toString()
)
}
}

println(Individual(“John”, 42).toString())
>>> Individual[name=John, age=42]

It’s doable in a document class to override the hashCode, equals, and toString strategies, successfully changing the JVM runtime generated strategies. On this case, the habits is user-defined for these strategies.

Report desugaring

Since information aren’t supported on any Android gadget in the present day, the D8/R8 desugaring engine must desugar information: it transforms the document code into code appropriate with the Android VMs. Report desugaring includes remodeling the document right into a roughly equal class, with out producing or compiling sources. The next Kotlin supply exhibits an approximation of the generated code. For the applying code measurement to stay small, information are desugared in order that helper strategies are shared in between information.

class PersonDesugared(val title: String, val age: Int) {
enjoyable getFieldsAsObjects(): Array<Any> {
return arrayOf(title, age)
}

override enjoyable hashCode(): Int {
return SharedRecordHelper.hash(
PersonDesugared::class.java,
getFieldsAsObjects())
}

override enjoyable equals(different: Any?): Boolean {
if (different == null || different !is PersonDesugared) {
return false
}
return getFieldsAsObjects().contentEquals(different.getFieldsAsObjects())
}

override enjoyable toString(): String {
return SharedRecordHelper.toString(
getFieldsAsObjects(),
PersonDesugared::class.java,
"title;age")
}

class SharedRecordHelper {
companion object {
enjoyable hash(recordClass: Class<*>, fieldValues: Array<Any>): Int {
return 31 * recordClass.hashCode() + fieldValues.contentHashCode()
}

enjoyable toString(
fieldValues: Array<Any>,
recordClass: Class<*>,
fieldNames: String
)
: String {
val fieldNamesSplit: Checklist<String> =
if (fieldNames.isEmpty()) emptyList() else fieldNames.cut up(";")
val builder: StringBuilder = StringBuilder()
builder.append(recordClass.simpleName).append("[")
for (i in fieldNamesSplit.indices) {
builder
.append(fieldNamesSplit[i])
.append("=")
.append(fieldValues[i])
if (i != fieldNamesSplit.measurement - 1) {
builder.append(", ")
}
}
builder.append("]")
return builder.toString()
}
}
}
}

Report shrinking

R8 assumes that the default hashCode, equals, and toString strategies generated by javac successfully symbolize the inner state of the document. Due to this fact, if a subject is minified, the strategies ought to replicate that; toString ought to print the minified title. If a subject is eliminated, for instance as a result of it has a relentless worth throughout all situations, then the strategies ought to replicate that; the sector is ignored by the hashCode, equals, and toString strategies. When R8 makes use of the document construction within the strategies generated by javac, for instance when it seems to be up fields within the document or inspects the printed document construction, it is utilizing reflection. As is the case for any use of reflection, you will need to write hold guidelines to tell the shrinker of the reflective use in order that it might probably protect the construction.

In our instance, assume that age is the fixed 42 throughout the applying whereas title isn’t fixed throughout the applying. Then toString returns totally different outcomes relying on the foundations you set:

Individual(“John”, 42).toString();

>>> Individual[name=John, age=42]

>>> a[a=John]

>>> Individual[b=John]

>>> a[name=John]

>>> a[a=John, b=42]

>>> Individual[name=John, age=42]

Reflective use instances

Protect toString habits

Say you have got code that makes use of the precise printing of the document and expects it to be unchanged. For that you will need to hold the complete content material of the document fields with a rule comparable to:

-keep,allowshrinking class Individual
-keepclassmembers,allowoptimization class Individual { <fields>; }

This ensures that if the Individual document is retained within the output, any toString callproduces the very same string as it might within the authentic program. For instance:

Individual("John", 42).toString();
>>> Individual[name=John, age=42]

Nevertheless, if you happen to solely need to protect the printing for the fields which are really used, you possibly can let the unused fields to be eliminated or shrunk with allowshrinking:

-keep,allowshrinking class Individual
-keepclassmembers,allowshrinking,allowoptimization class Individual { <fields>; }

With this rule, the compiler drops the age subject:

Individual("John", 42).toString();
>>> Individual[name=John]

Protect document members for reflective lookup

If you have to reflectively entry a document member, you sometimes must entry its accessor methodology. For that you will need to hold the accessor methodology:

-keep,allowshrinking class Individual
-keepclassmembers,allowoptimization class Individual { java.lang.String title(); }

Now if situations of Individual are within the residual program you possibly can safely search for the existence of the accessor reflectively:

Individual("John", 42)::class.java.getDeclaredMethod("title").invoke(obj);
>>> John

Discover that the earlier code accesses the document subject utilizing the accessor. For direct subject entry, you have to hold the sector itself:

-keep,allowshrinking class Individual
-keepclassmembers,allowoptimization class Individual { java.lang.String title; }

Construct techniques and the Report class

Should you’re utilizing one other construct system than AGP, utilizing information could require you to adapt the construct system. The java.lang.Report class isn’t current till Android 14, launched within the SDK from “Android UpsideDownCake Preview” revision 4. D8/R8 introduces the com.android.instruments.r8.RecordTag, an empty class, to point {that a} document subclass is a document. The RecordTag is used in order that directions referencing java.lang.Report can instantly be rewritten by desugaring to reference RecordTag and nonetheless work (instanceof, methodology and subject signatures, and so forth.).

Because of this every construct containing a reference to java.lang.Report generates an artificial RecordTag class. In a state of affairs the place an software is cut up in shards, every shard being compiled to a dex file, and the dex information put collectively with out merging within the Android software, this might result in duplicate RecordTag class.

To keep away from the problem, any D8 intermediate construct generates the RecordTag class as a world artificial, in a unique output than the dex file. The dex merge step is then capable of appropriately merge international synthetics to keep away from surprising runtime habits. Every construct system utilizing a number of compilation comparable to sharding or intermediate outputs is required to assist international synthetics to work appropriately. AGP absolutely helps information from model 8.1.

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