1, Definition

• In this article I will introduce to you about 1 type of object in RxJava. Although not as common as the Observable or the Observer, it combines the combined strength of both. That is the Subject.
• By the way, I have just returned to apply them and also to revise, in this article I will introduce to everyone about Subject types in RxJava. RxJava provides us with 4 types of Subjects:
  • Publish Subject.
  • Replay Subject.
  • Behavior Subject.
  • Async Subject.
• Subjects are objects in RxJava that can interact with other components such as an Observable and an Observer. In short, it carries the power of both:
  • Because the subject is an observer, it can subscribe to one or more observables.
  • Because the Subject is Observable, it can pass items to the Observer by re-emmiting or emit new items.
• Learning them through examples is an easy way to understand.
• Admit:
  • Observable: teachers. Teachers teach students lessons.
  • Observer: student. Students will follow the teacher’s lessons.

2, Subject types

2.1 Publish Subject

• If the student enters the classroom late, he only wants to listen at the time when he enters the classroom.

2.2 Replay Subject

• If the student enters the classroom late, he wants to listen to the beginning of the lecture.

2.3 Async Subject

• If the student enters the classroom at any one time, he just wants to hear the last thing.

2.4 Behavior Subject

• If the student was late, he just wanted to hear the nearest thing.

3, Summary

• Subject is less commonly used than Observable and Observer but is also very powerful and useful in many cases like Publish Subject used in Search.
• Hopefully the brief article will help everyone understand Subject better.