BehaviorSubject emits the most recent item it has observed and then all subsequent observed items to each subscribed Observer.

Class Declaration

Following is the declaration for io.reactivex.subjects.BehaviorSubject<T> class −

public final class BehaviorSubject<T>
extends Subject<T>

BehaviorSubject Example

Create the following Java program using any editor of your choice in, say, C:> RxJava.

ObservableTester.java

import io.reactivex.subjects.BehaviorSubject;
public class ObservableTester  {
   public static void main(String[] args) {   
      final StringBuilder result1 = new StringBuilder();
      final StringBuilder result2 = new StringBuilder();         
      BehaviorSubject<String> subject =  BehaviorSubject.create(); 
      subject.subscribe(value -> result1.append(value) ); 
      subject.onNext("a"); 
      subject.onNext("b"); 
      subject.onNext("c"); 
      subject.subscribe(value -> result2.append(value)); 
      subject.onNext("d"); 
      subject.onComplete();
      //Output will be abcd
      System.out.println(result1);
      //Output will be cd being BehaviorSubject 
      //(c is last item emitted before subscribe)
      System.out.println(result2);
   }
}

Verify the Result

Compile the class using javac compiler as follows −

C:RxJava>javac ObservableTester.java

Now run the ObservableTester as follows −

C:RxJava>java ObservableTester

It should produce the following output −

abcd
cd