Twitter4J is an unofficial Java library for the Twitter API. With Twitter4J, you can easily integrate your Java application with the Twitter service. Twitter4J is an unofficial library. For more information, visit Twitter4J homepage
What you can do with Twitter4J:
Updating status : You can update "What are you doing?" via Twitter.updateStatus() method.
Getting Timeline :Twitter.get****Timeline() returns a List of friends or specified user's home timeline.
Sending / Receiving Direct Messages : You can send and receive direct messages via Twitter.sendDirectMessage() / Twitter.getDirectMessages().
Search for Tweets : You can search for Tweets using Query class and Twitter.search(twitter4j.Query) method. This method allows specific tweets to be downloaded by specifying the keywords in the search query. With this search API, downloading can be limited. The search API only able to find tweets which are posted between 6-9 days in the past. Moreover, with this API, there is a limit of 1500 tweets (maximum) can be retrieved at a time.
Streaming API : TwitterStream class has several methods prepared for the streaming API. All you need is to have a class implementing StatusListener. Twitter4J will do creating a thread, consuming the stream. More tweets are retrieved than using search API and the number of tweets is unlimited.