What is JShell?

Small overview of fupcoming first official Java REPL
31 August 2017   570

JShell is Java’s first official REPL (READ-EVAL-PRINT-LOOP) tool. It is part of JDK 9 is going to be released in September 2017.

JShell REPL creates a simple programming environment in the command line that can:

  • read user's input
  • evaluate it
  • print the result
  • repeat the cycle

It works similar to Python interpreter or other JVM languages that have a REPL like Scala, Kotlin and Groovy.

You can write Java language expressions and statements in the JShell REPL, and they will be evaluated on their own without having to wrap them in classes or methods.

Let's take a look how to start with JShell.

As mentioned above, JShell is a part of upcoming Java 9. But eraly access is already available. 

When JDK 9 is installed, type jshell in your terminal to start a JShell session -

$ jshell
|  Welcome to JShell -- Version 9
|  For an introduction type: /help intro


An interactive JShell session will be started and JShell will greet you with a welcome message.

Learn more with this tutorial

What is Web3j?

Small review of lightweight Java and Android library for integration with Ethereum clients
15 December 2017   831

What is webj3?

web3j is a lightweight, highly modular, reactive, type safe Java and Android library for working with Smart Contracts and integrating with clients (nodes) on the Ethereum network:

web3j architecture
Web3j Architecture

This allows you to work with the Ethereum blockchain, without the additional overhead of having to write your own integration code for the platform.

According to the developers, these are the features:

  • Complete implementation of Ethereum's JSON-RPC client API over HTTP and IPC
  • Ethereum wallet support
  • Auto-generation of Java smart contract wrappers to create, deploy, transact with and call smart contracts from native Java code (Solidity and Truffle definition formats supported)
  • Reactive-functional API for working with filters
  • Ethereum Name Service (ENS) support
  • Support for Parity's Personal, and Geth's Personal client APIs
  • Support for Infura, so you don't have to run an Ethereum client yourself
  • Comprehensive integration tests demonstrating a number of the above scenarios
  • Command line tools
  • Android compatible
  • Support for JP Morgan's Quorum via web3j-quorum

It has five runtime dependencies:

  • RxJava for its reactive-functional API
  • OKHttp for HTTP connections
  • Jackson Core for fast JSON serialisation/deserialisation
  • Bouncy Castle (Spongy Castle on Android) for crypto
  • Jnr-unixsocket for *nix IPC (not available on Android)

It also uses JavaPoet for generating smart contract wrappers.

Lear more at GitHub.