The bitcoinj library is a Java implementation of the Bitcoin protocol, which allows it to maintain a wallet and send/receive transactions without needing a local copy of Bitcoin Core. It comes with full documentation and some example apps showing how to use it.
To get started, it is best to have the latest JDK and Gradle installed. The HEAD of the `master` branch contains the latest development code and various production releases are provided on feature branches.
If you are using Gradle 4.10 or later, the build will automatically include the JavaFX-based `wallettemplate` module. The outputs are under the `build` directory.
Alternatively, just import the project using your IDE. http://www.jetbrains.com/idea/download/[IntelliJ] has Gradle integration built-in and has a free Community Edition. Simply use `File | New | Project from Existing Sources` and locate the `build.gradle` in the root of the cloned project source tree.
The *bitcoinj* `wallettool` subproject includes a command-line Wallet Tool (`wallet-tool`) that can be used to create and manage *bitcoinj*-based wallets (both the HD keychain and SPV blockchain state.) Using `wallet-tool` on Bitcoin's test net is a great way to learn about Bitcoin and *bitcoinj*.
NOTE: These instructions are for macOS/Linux, for Windows use the `wallettool/build/install/wallet-tool/bin/wallet-tool.bat` batch file with the equivalent Windows command-line commands and options.
If you want to develop or test your app with a https://jitpack.io[Jitpack]-powered build of the latest `master` or `release-0.15` branch of *bitcoinj* follow the dynamically-generated instructions for that branch by following the correct link.