Stream is one of the most important and commonly used concepts in java. Streams are powerful and flexible, providing a mechanism for reading and writing data, and allowing you to build your own solution to handle a specific problem.

This article will help you understand what stream actually is, as well as its implementation in Java.

What Is Stream In Java And Its Types?

The is a new package in Java 8 that provides additional functionality. This package supports functional-style operations on elements through classes, interfaces, and enums. By importing the package, you can use stream.

A Java stream typically supports multiple devices, including keyboards, networking sockets, and disk files. Thus, it is convenient to handle various types of I/O operations similarly.

Streams in java fall into two basic types: byte streams and character streams. Byte stream classes allow inputs and outputs of bytes, while character stream classes allow inputs and outputs of characters.

Features of Streams in Java

The features of the stream are as follows:

  • There are no elements stored in the stream. Using a pipeline of computational operations, it conveys elements from a source (a data structure, an array, or an I/O channel).
  • The function is the essence of the stream. Stream operations do not alter their source. For instance, if you filter a Stream obtained from a collection, rather than removing elements from the collection from which the stream gets obtained, you end up with a new Stream without the filtered elements.
  • As a lazy evaluation system, streams evaluate code only when needed.
  • A stream only visits its elements once. For each source element to get revisited, a new stream must get generated.

Different Operations On Streams

Following are some of the operations that you can perform on Streams to get better values.

Intermediate Operations


This method returns a stream of elements after being applied to the specified function.

List num = Arrays.asList(2,3,4,5);
List sqr =>x*x).collect(Collectors.toList());


By using the filter method, you can select elements according to a predicate.

List name = Arrays.asList("Reflect","Collect","Streamline");
List output=>s.startsWith("S")).collect(Collectors.toList());


To sort the stream, we use the sorted method.

List name = Arrays.asList("Reflect","Collect","Streamline");
List output =;

Terminal Operations


Collection methods return the results of intermediate operations performed on a stream.

List num = Arrays.asList(2,3,4,5,3);
Set square =>x*x).collect(Collectors.toSet());


ForEach iterates through the stream element by element.

List number = Arrays.asList(2,3,4,5);>x*x).forEach(y->System.out.println(y));


When a stream contains multiple elements, the reduce method reduces them to one value. A BinaryOperator is passed as a parameter to reduce the method.

List number = Arrays.asList(2,3,4,5);
int even =>x%2==0).reduce(0,(ans,i)-> ans+i);

Initially, ans has 0 as its value, and I get added to it.

Java Stream Example

Filtering Collections with Streams. In this example, we are filtering data using a stream.

import java.util.*; 
class Product
    int id; 
    String name; 
    float price; 
    public Product(int prod_id, String prod_name, float prod_price) { = prod_id; = prod_name; 
        this.price = prod_price; 

public class JavaStreamExample
    public static void main(String[] args) { 
        List<Product> product_List = new ArrayList<Product>(); 
        //Adding Products 
        product_List.add(new Product(1,"HP Smart Laptop",28000f)); 
        product_List.add(new Product(2,"Sony Smart Laptop",20000f)); 
        product_List.add(new Product(3,"Lenevo Smart Laptop",32000f)); 
        product_List.add(new Product(4,"Xiaomi Smart Laptop",25000f)); 
        product_List.add(new Product(5,"Apple Smart Laptop",90000f)); 
        List<Float> productPriceList2 
                                    .filter(p -> p.price > 25000)// filtering data 
                                    .map(p->p.price)        // fetching price 
                                    .collect(Collectors.toList()); // collecting as list 


[28000.0, 32000.0, 90000.0]

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Stream operations are one of the most powerful tools in the Java collection framework. They provide many benefits with high performance, multiple functions support, and easier-to-understand abstraction over data sets.
The benefit of the stream is that it allows data processing to be performed lazily. This is the main reason why the Java Stream API is used so often within collection pipelines, whenever you need pre-calculating some processing on each element