Packages 
Package Description
org.bitcoin  
org.bitcoin.crawler  
org.bitcoin.protocols.payments  
org.bitcoinj.core
The core package contains classes for network messages like Block and Transaction, peer connectivity via PeerGroup, and block chain management.
org.bitcoinj.core.listeners  
org.bitcoinj.crypto
The crypto package contains classes that work with key derivation algorithms like scrypt (passwords to AES keys), BIP 32 hierarchies (chains of keys from a root seed), X.509 utilities for the payment protocol and other general cryptography tasks.
org.bitcoinj.jni  
org.bitcoinj.kits
High level wrapper APIs around the bitcoinj building blocks.
org.bitcoinj.net
Classes handling low level network management using either NIO (async io) or older style blocking sockets (useful for using SOCKS proxies, Tor, SSL etc).
org.bitcoinj.net.discovery
Classes that know how to discover peers in the P2P network using DNS or HTTP.
org.bitcoinj.params
Network parameters encapsulate some of the differences between different Bitcoin networks such as the main network, the testnet, regtest mode, unit testing params and so on.
org.bitcoinj.protocols.payments
The BIP70 payment protocol wraps Bitcoin transactions and adds various useful features like memos, refund addresses and authentication.
org.bitcoinj.script
Classes for working with and executing Bitcoin script programs, as embedded in inputs and outputs.
org.bitcoinj.signers
Transaction signers know how to calculate signatures over transactions in different contexts, for example, using local private keys or fetching them from remote servers.
org.bitcoinj.store
Block stores persist blockchain data downloaded from remote peers.
org.bitcoinj.uri
Parsing and handling of bitcoin: textual URIs as found in qr codes and web links.
org.bitcoinj.utils
Formatting monetary amounts, representing exchange rates, a program for loading Bitcoin Core saved block files, a class to control how bitcoinj uses threads and misc other utility classes that don't fit anywhere else.
org.bitcoinj.wallet
Classes that support the Wallet, which knows how to find and save transactions relevant to a set of keys or scripts, calculate balances, and spend money: the wallet has many features and can be extended in various ways, please refer to the website for documentation on how to use it.
org.bitcoinj.wallet.listeners