Streams in Java 8

Streams!!! A Java Interface to perform certain set of operations on bunch of items/data/elements serially or parallel.

It is a functional or declarative style of programming in java. streams doesn’t store any data with it so we can’t get a data by address or index.

Streams can be created on Collections, Arrays, or I/O resources.

Mode of Streams:-

The way of creation of initial stream will result 2 different streams. it can be Serial or Parallel.

1. Serial → streams()

it just work like for loop, one by one on single thread.

2. Parallel → parallelStream()

it will run on multiple threads.

import java.util.ArrayList;
import java.util.List;

public class StreamsUnderstanding{

    public static void main(String[] args) {
        List<Integer> productList = new ArrayList<Integer>();
        productList.add(1000);
        for (int i = 0; i < 6; i++) {
            int lastvalue = productList.get(i);
            productList.add(lastvalue+1000);
        }
        
        System.out.println("Input List --> "+productList);
        
        List serialList = new ArrayList();
        productList.stream().filter(p->p>3000).forEach(s->{
              System.out.println("Thread Name --> "+Thread.currentThread().getName());
                serialList.add(s);
            });
        System.out.println("Serial Stream --> "+serialList);
        List parallelList = new ArrayList();
        productList.parallelStream().filter(p->p>3000).forEach(s->{
             System.out.println("Thread Name --> "+Thread.currentThread().getName());
                parallelList.add(s);
            });
        
         System.out.println("Parallel Stream --> "+parallelList);
        }
    }
--------------------------------------------------------------------
Output:-
--------------------------------------------------------------------
Input List --> [1000, 2000, 3000, 4000, 5000, 6000, 7000]
Thread Name --> main
Thread Name --> main
Thread Name --> main
Thread Name --> main
Serial List --> [4000, 5000, 6000, 7000]
Thread Name --> ForkJoinPool.commonPool-worker-3
Thread Name --> ForkJoinPool.commonPool-worker-3
Thread Name --> main
Thread Name --> ForkJoinPool.commonPool-worker-2
Parallel List --> [5000, 4000, 6000, 7000]

Conversion of Streams:-

After the initial creation of Streams, it can be converted from Parallel to Sequential or vice versa..

/**
* sequential() - will convert Parallel stream to Serial Stream.
* parallel() - will convert Serial stream to Parallel Stream.
**/

Stream Operations:-

1. Intermediate
2. Terminal

Intermediate Operations:-

• it will return a new stream always.
• Statefull(Maintain whether visited or not) and stateless
• It is lazy

Terminal Operations:-

1. it is eager.

2. when the terminal operator is initiated stream pipeline will be executed sequentially or parallel.

Stream Pipeline:-

A stream pipeline consists of a source (such as a Collection, an array, a generator function, or an I/O channel); followed by zero or more intermediate operations such as Stream.filter or Stream.map; and a terminal operation such as Stream.forEach or Stream.reduce.

Stream Pipeline

Short-Circuits in Streams:-

Streams has couple of methods to disturb normal flow of intermediate and terminal operations. Examples:- limit(), findFirst(), findAny().