Observables

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RxJava Useful Resources

RxJava - Mathematical Operators

Quiz

Following are the operators which operates on entire items emitted by an Observable.

Sr.No.	Operator & Description
1	concat Emits all items from multiple Observable without interleaving.
2	count Counts all items and emit the result.
3	reduce Apply a function on each item and return the result.
4	sum Evaluates sum of all items and emit the result.

Example - Usage of count operator

ObservableTester.java

package com.tutorialspoint;

import io.reactivex.rxjava3.core.Observable;

//Using count operator to operate on an Observable
public class ObservableTester  {
   public static void main(String[] args) {    
      String[] letters = {"a", "b", "c", "d", "e", "f", "g"};
      Observable.fromArray(letters)
         .count()   
         .subscribe(System.out::println);
   }
}

Output

Compile and Run the code to verify the following output −

Example - Usage of reduce operator

ObservableTester.java

package com.tutorialspoint;

import io.reactivex.rxjava3.core.Observable;

//Using reduce operator to get sum of numbers
public class ObservableTester  {
   public static void main(String[] args) {    
      Observable.just(1,2,3,4,5,6,7)
         .reduce(0, (a,b) -> a + b) 
         .subscribe(s -> System.out.println("Sum: " + s));
   }
}

Output

Compile and Run the code to verify the following output −

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