I want to listen to real time all the tweets which has #abc #def hashtags for example,
preferred language is Java but raw API is great too
I couldn't find the documentation that describes it
I don't have experience with twitter4j, but what you'll need to utilize their Streaming API example.
From that you'll need to include filter method.
A more detailed example is found in this example
FilterQuery fq = new FilterQuery();
String keywords[] = {"ireland"};
fq.track(keywords);