# Android Integration Guide

Star Tower Core is available on the Android platform, through Java/JNI bindings. In this guide we show how to use it.

### Prerequisites <a href="#prerequisites" id="prerequisites"></a>

* *Android Studio*
* *Android NDK Support plugin*

Android releases are hosted on GitHub packages, It needs authentication to download packages, please checkout this guide from GitHub for more details.

We recommend to create a non-expiring and readonly token for accessing GitHub packages, and add it to `local.properties` of your Android Studio project locally.

Generate a token [here](https://github.com/settings/tokens):![](/files/2yVrN3AgoFf9sjRgKLEX)

Add this dependency to build.gradle:

```
dependencies {
    implementation "FR.startower:starower-core:<latest_tag>"
}
```

Add `maven` and `credentials` (`local.properties` for local or system environment variables CI)

```

Properties properties = new Properties()
File localProps = new File(rootDir.absolutePath, "local.properties")
if (localProps.exists()) {
    properties.load(localProps.newDataInputStream())
} else {
    println "local.properties not found"
}

allprojects {
    repositories {
        maven {
            url = uri("https://maven.pkg.github.com/startower/wallet-core")
            credentials {
                username = properties.getProperty("gpr.user") as String?: System.getenv("GITHUB_USER")
                password = properties.getProperty("gpr.key") as String?: System.getenv("GITHUB_TOKEN")
            }
        }
    }
}
```

### Code Examples <a href="#code-examples" id="code-examples"></a>

In the following sections we show code examples for some common funcions.

#### Wallet Management <a href="#wallet-management" id="wallet-management"></a>

First thing we need is to load JNI library

```
init {
    System.loadLibrary("StarTowerWalletCore")
}
```

Creating or Importing a Multi-Coin HD Wallet

```
val wallet = HDWallet(128, "")
```

```
val wallet = HDWallet("ripple scissors kick mammal hire column oak again sun offer wealth
```

#### Transaction Signing <a href="#transaction-signing" id="transaction-signing"></a>

In general, when creating a new blockchain transaction, a wallet has to:

1. Put together a transaction with relevant fields (source, target, amount, etc.)
2. Sign the transaction, using the account private key. This is done by StarTower Core.
3. Send to a node for broadcasting to the blockchain network.

Ethereum Transaction Signing

Code example to fill in signer input parameters, perform signing, and retrieve encoded result:

```
val signerInput = Ethereum.SigningInput.newBuilder().apply {
    chainId = ByteString.copyFrom(BigInteger("01").toByteArray())
    gasPrice = BigInteger("d693a400", 16).toByteString() // decimal 3600000000
    gasLimit = BigInteger("5208", 16).toByteString()     // decimal 21000
    toAddress = dummyReceiverAddress
    transaction = Ethereum.Transaction.newBuilder().apply {
       transfer = Ethereum.Transaction.Transfer.newBuilder().apply {
           amount = BigInteger("0348bca5a16000", 16).toByteString()
       }.build()
    }.build()
    privateKey = ByteString.copyFrom(secretPrivateKey.data())
}.build()
val output = AnySigner.sign(signerInput, CoinType.ETHEREUM, Ethereum.SigningOutput.parser())
println("Signed transaction: \n${signerOutput.encoded.toByteArray().toHexString()}")
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://developer.startower.fr/get-started/developing-for-star-tower-wallet-platform/integration-guide/android-integration-guide.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.