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I worked with web3js(JavaScript) and used web3.eth.Contract with 2 params (json, address) and successfully got contract object. Now I started to work with web3j(Java) and don`t understand how I have to work now. How can I do this ?

  • Like java and javascript are totally unrelated languages, web3j is different from the javascript library with similar name. I'd suggest to start reading web3j's documentation at docs.web3j.io. – Ismael Sep 3 at 16:44
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    Yes, I found this documentation, but it doesn`t clarify what exactly I have to do. It seems to me, that I need to deploy somehow a contract via Solidity or Truffle. Both of them I did not use before. So, how can I deploy a contract having json and address - that is a question) May be someone has an example ? – Alexander_K Sep 4 at 7:25
  • Last time I did something with java you had to use some utility to convert json file to a smart contract wrapper. Then use that wrapper to deploy instances or interact with deployed instances, see docs.web3j.io/getting_started/…. Sorry, but I did use very little of web3j so I can't help much there. – Ismael Sep 4 at 16:58
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I found a solution

I installed epirus wrapper, then I generated java package with command epirus solidity generate

-a=/root/my_json.abi -o=/root/ -p=my_java

(before I changed extension of my file from json to abi). After getting this package, I could use smart contract object with his methods from json file.

Also, after installation of epirus and before generating package I used this commands

JAVA_HOME=$(dirname $( readlink -f $(which java) ))
JAVA_HOME=$(realpath "$JAVA_HOME"/../)
export JAVA_HOME

sudo update-alternatives --config java

Don`t know exactly what they do, but without them I could not use epirus.

To check if epirus ready to generate I used command

epirus -V 

It returns version of wrapper. If not - use two commands above.

Ismael, thank you for the direction)

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