1Use in Kotlin {#flatbuffers_guide_use_kotlin}
2==============
3
4## Before you get started
5
6Before diving into the FlatBuffers usage in Kotlin, it should be noted that
7the [Tutorial](@ref flatbuffers_guide_tutorial) page has a complete guide to
8general FlatBuffers usage in all of the supported languages (including K).
9
10This page is designed to cover the nuances of FlatBuffers usage, specific to Kotlin.
11
12You should also have read the [Building](@ref flatbuffers_guide_building)
13documentation to build `flatc` and should be familiar with
14[Using the schema compiler](@ref flatbuffers_guide_using_schema_compiler) and
15[Writing a schema](@ref flatbuffers_guide_writing_schema).
16
17## Kotlin and FlatBuffers Java code location
18
19Code generated for Kotlin currently uses the flatbuffers java runtime library. That means that Kotlin generated code can only have Java virtual machine as target architecture (which includes Android). Kotlin Native and Kotlin.js are currently not supported.
20
21The code for the FlatBuffers Java library can be found at
22`flatbuffers/java/com/google/flatbuffers`. You can browse the library on the
23[FlatBuffers GitHub page](https://github.com/google/flatbuffers/tree/master/
24java/com/google/flatbuffers).
25
26## Testing FlatBuffers Kotlin
27
28The test code for Java is located in [KotlinTest.java](https://github.com/google
29/flatbuffers/blob/master/tests/KotlinTest.kt).
30
31To run the tests, use [KotlinTest.sh](https://github.com/google/
32flatbuffers/blob/master/tests/KotlinTest.sh) shell script.
33
34*Note: These scripts require that [Kotlin](https://kotlinlang.org/) is installed.*
35
36## Using the FlatBuffers Kotlin library
37
38*Note: See [Tutorial](@ref flatbuffers_guide_tutorial) for a more in-depth
39example of how to use FlatBuffers in Kotlin.*
40
41FlatBuffers supports reading and writing binary FlatBuffers in Kotlin.
42
43To use FlatBuffers in your own code, first generate Java classes from your
44schema with the `--kotlin` option to `flatc`.
45Then you can include both FlatBuffers and the generated code to read
46or write a FlatBuffer.
47
48For example, here is how you would read a FlatBuffer binary file in Kotlin:
49First, import the library and generated code. Then, you read a FlatBuffer binary
50file into a `ByteArray`. You then turn the `ByteArray` into a `ByteBuffer`, which you
51pass to the `getRootAsMyRootType` function:
52
53~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.kt}
54 import MyGame.Example.*
55 import com.google.flatbuffers.FlatBufferBuilder
56
57 // This snippet ignores exceptions for brevity.
58 val data = RandomAccessFile(File("monsterdata_test.mon"), "r").use {
59 val temp = ByteArray(it.length().toInt())
60 it.readFully(temp)
61 temp
62 }
63
64 val bb = ByteBuffer.wrap(data)
65 val monster = Monster.getRootAsMonster(bb)
66~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
67
68Now you can access the data from the `Monster monster`:
69
70~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.kt}
71 val hp = monster.hp
72 val pos = monster.pos!!;
73~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
74
75
76
77## Differences between Kotlin and Java code
78
79Kotlin generated code was designed to be as close as possible to the java counterpart, as for now, we only support kotlin on java virtual machine. So the differences in implementation and usage are basically the ones introduced by the Kotlin language itself. You can find more in-depth information [here](https://kotlinlang.org/docs/reference/comparison-to-java.html).
80
81The most obvious ones are:
82
83* Fields as accessed as Kotlin [properties](https://kotlinlang.org/docs/reference/properties.html)
84* Static methods are accessed in [companion object](https://kotlinlang.org/docs/reference/classes.html#companion-objects)View as plain text