# 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):![](https://1817686354-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FbrS1XyBOhxXAZTMGmUZJ%2Fuploads%2Fm2sOoRtnXR8fJ5eLnEPs%2Fimage.png?alt=media\&token=80727b27-3f5d-4e03-bb3d-3827041ad451)

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()}")
```