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Data in Android Studio Flamingo

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Data in Android Studio Flamingo



Data in Android Studio Flamingo

Posted by Clément Béra, Senior software program engineer

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

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

The construct.gradle file additionally must be prolonged to make use of the right SDK and Java supply and goal. At present the Android UpsideDownCake Preview is required, however when the Android 14 last 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'
}
}

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

public document Particular person(String title, int age) {}

Moreover the document flags and attributes, the document Particular person 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(Particular person(“John”, 42).toString())
>>> Particular person[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.

File desugaring

Since information are usually not supported on any Android system right now, the D8/R8 desugaring engine must desugar information: it transforms the document code into code suitable with the Android VMs. File desugaring entails remodeling the document right into a roughly equal class, with out producing or compiling sources. The next Kotlin supply reveals an approximation of the generated code. For the appliance code dimension 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.break 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.dimension - 1) {
builder.append(", ")
}
}
builder.append("]")
return builder.toString()
}
}
}
}

File shrinking

R8 assumes that the default hashCode, equals, and toString strategies generated by javac successfully signify the interior state of the document. Subsequently, 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 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 should write hold guidelines to tell the shrinker of the reflective use in order that it could protect the construction.

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

Particular person(“John”, 42).toString();

>>> Particular person[name=John, age=42]

>>> a[a=John]

>>> Particular person[b=John]

>>> a[name=John]

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

>>> Particular person[name=John, age=42]

Reflective use instances

Protect toString habits

Say you’ve got code that makes use of the precise printing of the document and expects it to be unchanged. For that you should hold the complete content material of the document fields with a rule corresponding to:

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

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

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

Nevertheless, when you solely need to protect the printing for the fields which might be really used, you’ll be able to let the unused fields to be eliminated or shrunk with allowshrinking:

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

With this rule, the compiler drops the age subject:

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

Protect document members for reflective lookup

If it’s essential reflectively entry a document member, you sometimes have to entry its accessor methodology. For that you should hold the accessor methodology:

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

Now if situations of Particular person are within the residual program you’ll be able to safely search for the existence of the accessor reflectively:

Particular person("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, it’s essential hold the sector itself:

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

Construct techniques and the File class

For those who’re utilizing one other construct system than AGP, utilizing information could require you to adapt the construct system. The java.lang.File class will not be 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.File can straight be rewritten by desugaring to reference RecordTag and nonetheless work (instanceof, methodology and subject signatures, and so on.).

Because of this every construct containing a reference to java.lang.File generates an artificial RecordTag class. In a state of affairs the place an software is break up in shards, every shard being compiled to a dex file, and the dex recordsdata 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 special output than the dex file. The dex merge step is then in a position to appropriately merge international synthetics to keep away from surprising runtime habits. Every construct system utilizing a number of compilation corresponding to sharding or intermediate outputs is required to help international synthetics to work appropriately. AGP totally helps information from model 8.1.

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