web3j-android error: static interface method calls are not supported at language level 1.7

Question

I get this error

static interface method calls are not supported at language level 1.7

when having

Web3j web3j = Web3j.build(new HttpService(url));

documentation here says for Android you should use this instead of Web3j.build():

Web3jFactory.build(new HttpService());

But Web3jFactory isn't there. I have no such file for the import that should be (what I found if correct)

import org.web3j.protocol.Web3jFactory;

Here my build.gradle (reduced to relevant information)

apply plugin: 'java'

repositories {
    google()
    jcenter()
}

dependencies {
    implementation 'org.web3j:core:3.3.1-android'
    implementation group: 'org.web3j', name: 'infura', version: '3.3.1'
}

Answer 1

In the latest version of the web3j-android library 'org.web3j:core:4.1.0-android', org.web3j.protocol.Web3jFactory is indeed removed. However, the documentation still says we should use it. I believe they haven't updated the documentation yet.

Instead, we should actually use the regular one:

Web3j web3j = Web3j.build(new HttpService(url));

*Note: This method is a static interface method and it's only supported in Java 8 or version 1.8

So, if your android project is still using Java 7, be sure to update your android plugin and enable Java 8 like this https://developer.android.com/studio/write/java8-support. The error will be gone and you are good to go.

Else, you could also head over to the error that says not supported, press alt+enter and select 'Set language level to 8...'

https://ethereum.stackexchange.com/a/49371/50785 is not the permanent solution I think...

Answer 2

If you use kotlin version you may code like this:

private var web3: Web3j? = Web3j.build(HttpService("https://ropsten.infura.io/v3/youtoken"))
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val web3ClientVersion = web3!!.web3ClientVersion().sendAsync().get()
        val clientVersion = web3ClientVersion.getWeb3ClientVersion()
        print("Connected to Ethereum client version: $clientVersion")
    }

Answer 3

I got around this problem by using this code instead which is also what Web3j.build() does if you call it

Web3j web3j = new JsonRpc2_0Web3j(httpServiceProvider.getService(url));

But meanwhile it even works with Web3jFactory for some reason!?

So if you run in this problem you can use the code above as workaround and I guess you can also leave it like that as permanent solution

Answer 4

This fixed it for me: https://developer.android.com/studio/write/java8-support. The layout is relatively similar to the newest versions of AndroidStudio.