ICON

<p><strong>Espanicon </strong>is a validator on the ICON network. Their goal is to participate in the chain governance of the network and expand the ICON ecosystem by building projects in it and collaborating with other validators.</p><h2 id="header-0">Introduction</h2><p>A smart contract is a self-contained program that is stored and replicated on a blockchain network. When a contract is deployed to the blockchain, it becomes a part of the blockchain and is stored on every node in the network.</p><p>In the following guide we are going to explain in detail the process of:</p><ul><li>Setting up the development environment for writing a smart contract on ICON</li><li>Writing a sample smart contract that will work as a poll for people to cast a vote “Yes” or “No”.</li><li>Compile, optimize and deploy the smart contract.</li><li>And finally we are going to interact with the smart contract via RPC calls.</li></ul><h2 id="header-1">Setting up the development environment</h2><h3 id="prerequisites">Prerequisites</h3><p>For setting the development environment we need to install the following programs:</p><ul><li>Install OpenJDK, go, and goloop. <a href="https://docs.icon.community/concepts/computational-utilities/goloop/setup" rel="noopener noreferrer nofollow">Follow these instructions to install goloop</a> (this has instructions for OpenJDK, go and goloop).</li><li><a href="https://docs.gradle.org/current/userguide/installation.html" rel="noopener noreferrer nofollow">Install gradle</a></li></ul><p>For the smart contract deployment you can either choose to deploy on a testnet in the ICON Blockchain or run a local network.</p><p>If you want to deploy to a testnet you will need to have ICX in your selected testnet, for that you can use the following faucet:</p><ul><li><a href="https://faucet.iconosphere.io/" rel="noopener noreferrer nofollow">https://faucet.iconosphere.io/</a></li></ul><p>For setting up a local network, you can follow this guide</p><ul><li><a href="https://docs.icon.community/getting-started/how-to-run-a-local-network" rel="noopener noreferrer nofollow">https://docs.icon.community/getting-started/how-to-run-a-local-network</a></li></ul><h3 id="creating-the-project-workspace-with-gradle">Creating the project workspace with gradle</h3><p>We are going to be working on a folder named poll-contract inside our home folder, you can use any folder of your choice in your computer.</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>Inside the folder we are going to initialize a project using gradle. If you are unfamiliar with gradle please refer to <a href="https://docs.gradle.org/current/userguide/what_is_gradle.html" rel="noopener noreferrer nofollow">their documentation</a>.</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>The selected options are the following:</p><ul><li>Select type of project to generate: 2</li><li>Select implementation language: 3</li><li>Split functionality across multiple sub-projects?: 1</li><li>Select build script DSL: 1</li><li>Generate build using new APIs and behavior (some features may change in the next minor release)? (default: no) [yes, no] yes</li><li>Select test framework: 4</li><li>Project name (default: poll-contract): poll-contract</li><li>Source package (default: poll.contract): poll.contract</li></ul><p>The following folder structure will be created:</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>The build.gradle file is used to create <a href="https://docs.gradle.org/current/userguide/writing_build_scripts.html" rel="noopener noreferrer nofollow">build scripts</a>. In ICON, we use it to specify dependencies and write tasks.</p><p>After creating the workspace, you need to create one build.gradle file at the root of the project with the following code.</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>This specifies the project to use the <a href="https://github.com/icon-project/gradle-javaee-plugin" rel="noopener noreferrer nofollow">gradle javaee plugin</a> which is specifically created for smart contract development in ICON. Each subproject (in above tree structure, app folder) would have its own build.gradle file. There are 2 additional tasks you would need to add to optimize and deploy the jar file.</p><p>Edit the app/build.gradle file to have the following data:</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>In the optimizedJar task, mainClassName refers to the class which would be the entry point for the smart contract.</p><p>To avoid errors during compilation edit the app/src/test/java/poll/contract/AppTest.java file to have the following code:</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><h2 id="header-2">Writing and compiling the smart contract</h2><p>For this tutorial we are going to be creating a smart contract that would work as a poll, it allows for addresses to vote either “yes” or “no” and has methods to check an address vote and the vote count. After creating the smart contract we compile it, optimize the code for the ICON Blockchain and then deploy it to a local network in our computer.</p><h3 id="writing-the-smart-contract">Writing the smart contract</h3><p>Edit the app/src/main/java/poll/contract/App.java to have the following code:</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><h3 id="compiling-the-smart-contract">Compiling the smart contract</h3><p>To build the project and have it ready to deploy into the ICON Blockchain we run the following commands:</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>After running these commands the folder ./app/build/libs/ (along with an assortment of other files and folders) will be created by gradle with the following content:</p><p>-&gt; View code <a href="https://icon.community/tutorials/java-tutorial-part-1-setting-development-environment-and-writing-smart-contract/" rel="noopener noreferrer nofollow">here</a>.</p><p>The file that we are going to deploy into the ICON Blockchain is poll-contract-optimized.jar.</p><h2 id="header-3">Further Resources</h2><ul><li>Smart contracts in the official docs: <a href="https://docs.icon.community/icon-stack/smart-contracts" rel="noopener noreferrer nofollow">https://docs.icon.community/icon-stack/smart-contracts</a></li><li>Java score examples: <a href="https://github.com/icon-project/java-score-examples" rel="noopener noreferrer nofollow">https://github.com/icon-project/java-score-examples</a></li><li>Javaee scorex: <a href="https://github.com/icon-project/javaee-scorex" rel="noopener noreferrer nofollow">https://github.com/icon-project/javaee-scorex</a></li><li>javaee module source: <a href="https://github.com/icon-project/goloop/tree/master/javaee/api/src/java/score" rel="noopener noreferrer nofollow">https://github.com/icon-project/goloop/tree/master/javaee/api/src/java/score</a></li><li>Chain score sample: <a href="https://github.com/icon-project/goloop/blob/master/testsuite/java/foundation/icon/test/score/ChainScore.java" rel="noopener noreferrer nofollow">https://github.com/icon-project/goloop/blob/master/testsuite/java/foundation/icon/test/score/ChainScore.java</a></li><li>javaee api docs: <a href="https://www.javadoc.io/doc/foundation.icon/javaee-api/latest/index.html" rel="noopener noreferrer nofollow">https://www.javadoc.io/doc/foundation.icon/javaee-api/latest/index.html</a></li><li>javaee unittest api docs: <a href="https://www.javadoc.io/doc/foundation.icon/javaee-unittest/0.9.7/index.html" rel="noopener noreferrer nofollow">https://www.javadoc.io/doc/foundation.icon/javaee-unittest/0.9.7/index.html</a></li><li>javaee unittest source: <a href="https://github.com/icon-project/javaee-unittest" rel="noopener noreferrer nofollow">https://github.com/icon-project/javaee-unittest</a></li></ul>

Java Tutorial Part 1: Setting Development Environment and Writing Smart Contract

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ICON Network

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