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Table of contents
1.
Introduction
2.
Use of Stream in Java
3.
How to Create Java Stream?
4.
Syntax
5.
Java Stream Features
5.1.
Simplicity
5.2.
Flexibility
5.3.
Efficiency
5.4.
Parallel Processing
5.5.
Functional Style
6.
Different Operations On Streams
7.
Intermediate Operations
7.1.
Characteristics of Intermediate Operations
7.1.1.
Chaining
7.1.2.
Non-finalizing
7.1.3.
Lazy
7.2.
Important Intermediate Operations
7.2.1.
filter
7.2.2.
map
7.2.3.
sorted
8.
Terminal Operations
8.1.
Characteristics 
8.1.1.
Consuming
8.1.2.
Triggering
8.1.3.
Producing a Result
8.1.4.
Non-reusable
8.2.
Important Terminal Operations
8.2.1.
forEach
8.2.2.
collect
8.2.3.
reduce
9.
Benefit of Java Stream
9.1.
Error Reduction
9.2.
Enhanced Productivity
9.3.
Seamless Integration
9.4.
Improved Maintainability
9.5.
Readability
9.6.
Less Code
9.7.
Versatility
9.8.
Parallel Processing
9.9.
Functional Programming
10.
Example of Java Stream
11.
Important Points/Observations of Java Stream
11.1.
Streams are not data structures
11.2.
Streams are lazy
11.3.
Streams can be used only once
11.4.
Order matters
11.5.
Use parallel streams carefully
12.
Frequently Asked Questions
12.1.
Can I reuse a Java Stream after a terminal operation?
12.2.
How do I choose between a sequential and parallel stream?
12.3.
Are streams better than loops?
13.
Conclusion
Last Updated: Mar 27, 2024
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Java Stream

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Introduction

Java streams are like a smart tool in your coding toolbox that helps you handle lists or sets of data in a smooth, easy way. Imagine you have a bunch of tasks to do with your data - like sorting it, filtering out what you don't need, or doing some calculations. Java streams let you do all that in a straightforward, step-by-step manner without getting lost in complex code. 

Java Stream

In this article, we'll walk through what Java streams are, how to use them, and why they're helpful for coding projects. 

Use of Stream in Java

Java streams are a way to work with collections of data, like lists or arrays, in a very neat way. Before streams, if you wanted to do things like filter out certain elements from a list or combine elements in some way, you'd have to write loops and a lot of extra code. It was doable, but it could get complicated and hard to read, especially for big tasks.

With streams, you can do all these things in a more straightforward manner. For example, if you have a list of numbers and you only want the even ones, you can use a stream to filter them out with just one line of code. Streams make your code cleaner and easier to understand because they let you describe what you want to do with your data more directly.

They're especially useful when you're dealing with big collections of data and you need to do a lot of operations, like sorting, filtering, or mapping (which is applying some function to each element in the collection). Streams can handle all these tasks in a more efficient way, often with less code than the old loop-based methods.

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How to Create Java Stream?

Creating a Java Stream is pretty straightforward. It's like turning on a water tap but for your data. You start with a source, which can be a collection like a list or an array, and then you create a stream from it. Here's how you do it:

If you have a list of items, let's say a list of names, you can create a stream using the .stream() method attached to the list. It looks something like this:

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
Stream<String> namesStream = names.stream();


This line of code creates a stream that will let you work with the names in the list one by one.

For arrays, you can use Arrays.stream(array) to create a stream. If you have an array of numbers, for example, you'd do it like this:

int[] numbers = {1, 2, 3, 4, 5};
IntStream numbersStream = Arrays.stream(numbers);


And just like that, you've got a stream of numbers ready to be processed.

Syntax

In Java, streams have a specific way of writing code, which is known as syntax. The syntax for streams is designed to be clear and to the point, making it easier for you to tell the computer what you want to do with your data. Here's a basic outline of how it looks:

streamSource.operation().anotherOperation().finalOperation();

 

  • streamSource is where your stream starts. This could be a list, an array, or any other collection of data that you turn into a stream.
     
  • operation() represents the actions you want to perform on your data, like filtering, sorting, or mapping. You can chain together as many of these as you need.
     
  • finalOperation() is usually the step where you collect your results or perform an action that ends the stream, like printing out the values.
     

Here's an example of using a stream with a list of numbers to filter out the even ones and print them:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
numbers.stream()           // Turns the list into a stream
       .filter(n -> n % 2 == 0)  // Keeps only the even numbers
       .forEach(System.out::println); // Prints each remaining number


In this code:

.stream() turns the list numbers into a stream.

.filter(n -> n % 2 == 0) removes any number that's not even.

.forEach(System.out::println) takes each number that made it through the filter and prints it out.

Java Stream Features

Java Streams come packed with features that make them super useful for working with collections of data. Here are a few key features that stand out:

Simplicity

Streams make it simpler to perform complex data operations with minimal code. You can filter, sort, and transform data using simple, readable commands.

Flexibility

You can use streams with any collection of data, like lists or arrays, making them versatile tools in your programming kit.

Efficiency

Streams are designed to be efficient, especially when working with large datasets. They use a technique called "lazy evaluation," which means they only process data when it's absolutely necessary.

Parallel Processing

One of the coolest things about streams is their ability to process data in parallel. This means they can split the data into chunks and work on each chunk simultaneously, speeding up the processing time.

Functional Style

Streams work well with Java's functional programming features, like lambda expressions. This allows for clear and concise code that's focused on the "what" rather than the "how" of data processing.

Different Operations On Streams

In Java streams, you can perform a bunch of different operations to manipulate your data. These operations are mainly divided into two types: Intermediate Operations and Terminal Operations.

Intermediate Operations

These operations help you shape your stream without finishing it. Think of them as steps in a recipe that prepare your ingredients but don't complete the dish. They're called "intermediate" because you can chain multiple of these operations one after the other. Examples include filter, which removes elements based on a condition, and map, which transforms each element in the stream.

Characteristics of Intermediate Operations

Chaining

You can link these operations one after another to perform complex tasks in a streamlined way.

Non-finalizing

They don't end the stream. You can keep using more operations after them.

Lazy

They wait until a terminal operation is applied before they actually do anything. This saves time by only processing what's needed.

Important Intermediate Operations

filter

Picks out elements that match a condition. For example, filtering a list of numbers to only include the even ones.

map

Changes each element in the stream to something else. Like turning a list of names into a list of their lengths.

sorted

Arranges the elements in a certain order, either the natural order or one you specify.

Terminal Operations

These operations end the stream. They're like the final step in your recipe that serves the dish. Once you apply a terminal operation, the stream is consumed and can no longer be used. Common terminal operations include forEach, which does something with each element of the stream, and collect, which gathers the final results into a collection.

Characteristics 

Consuming

Terminal operations consume the stream, meaning that once a terminal operation is applied, the stream cannot be used anymore. It's like the final checkout in a shopping process; once you're done, you leave the store.

Triggering

They trigger the execution of all the preceding operations in the stream pipeline. Unlike intermediate operations, which are lazy and wait around, terminal operations get things moving. It's like pressing the "play" button on a series of actions.

Producing a Result

Every terminal operation produces a result. This could be a value, like a sum or an average, a collection of elements, or even nothing at all (in cases where the operation's purpose is to cause an effect, such as printing out each element).

Non-reusable

Once a terminal operation has been applied and the stream has been consumed, you cannot reuse the same stream. If you need to perform operations on the same data again, you'll have to create a new stream.

Important Terminal Operations

forEach

This operation goes through each element of the stream and does something with it, like printing it out. It's a way to take action on your data.

collect

Gathers the elements into a collection, like a list or a set. This is super useful when you want to get your data out of the stream and work with it in a more traditional way.

reduce

This combines all elements in the stream into a single result. For example, you can use reduce to add up a bunch of numbers.

Terminal operations are crucial because they trigger the processing of all the intermediate operations you've set up. They bring everything together and give you the final output you've been working towards.

Benefit of Java Stream

Java stream have many benefits, like -: 

Error Reduction

By using streams, you're likely to reduce the chance of errors in your code. Since streams encourage a more declarative approach to data processing, where you specify what you want to achieve without having to spell out how it's done step by step, there's less room for mistakes like off-by-one errors in loops or incorrect conditionals.

Enhanced Productivity

When you're working with streams, you can achieve more with less code, which boosts your productivity. The streamlined syntax and powerful operations available with streams mean you spend less time writing boilerplate code and more time focusing on the logic specific to your application.

Seamless Integration

Streams integrate seamlessly with the rest of the Java language and its APIs. This means you can easily combine streams with other features of Java, like Optional, the Collections Framework, and new features introduced in later Java versions, making your code more modern and aligned with current Java best practices.

Improved Maintainability

Code that's easier to read and understand is also easier to maintain. With streams, your data processing logic is more transparent, making it simpler for you or others to modify and extend your code in the future without introducing bugs.

Readability

Streams can make your code easier to read & understand. With streams, what you're trying to do with your data is clear & straightforward.

Less Code

Often, you can do complex tasks with less code compared to older methods. This makes your programs shorter & cleaner.

Versatility

You can use streams with any kind of collection of data, like lists, sets, or arrays. This makes them very flexible tools.

Parallel Processing

Streams can easily handle data in parallel, which means they can process big chunks of data faster by using multiple cores of your computer's CPU.

Functional Programming

Streams work well with Java's functional programming features, like lambda expressions. This lets you write more declarative code, focusing on the "what" rather than the "how."

Example of Java Stream

To show how Java streams work in practice, let's look at a simple example. Imagine you have a list of names, and you want to find out which ones start with the letter "A" and print them out. Here's how you could do it using a Java stream:

First, we create a list of names:

List<String> names = Arrays.asList("Alice", "Bob", "Alex", "Charlie", "Amanda");


Now, we use a stream to filter and print the names that start with "A":

names.stream()                          // Convert the list to a stream
     .filter(name -> name.startsWith("A"))  // Use filter to keep only names that start with "A"
     .forEach(System.out::println);         // Print each name that made it through the filter


This code snippet will output:

Alice
Alex
Amanda


In this example, .stream() turns our list of names into a stream. .filter(name -> name.startsWith("A")) is an intermediate operation that keeps only the names starting with "A". Finally, .forEach(System.out::println) is a terminal operation that prints out each name in the resulting stream.

Important Points/Observations of Java Stream

When working with Java streams, there are a few important points and observations that can help you use them more effectively. Here's what you should keep in mind:

Streams are not data structures

They don't store data like a list or array. Instead, they carry data from a source through a pipeline of operations.

Streams are lazy

Many stream operations won't start until they're needed. This means that if you set up a stream pipeline but don't use a terminal operation to end it, no processing happens.

Streams can be used only once

After a terminal operation is applied, the stream is considered consumed and can't be used again. If you need to process the same data again, you'll need to create a new stream.

Order matters

The order in which you arrange your intermediate operations can affect the performance of your stream pipeline. For example, it's usually more efficient to filter your data before mapping it.

Use parallel streams carefully

Parallel streams can improve performance by using multiple threads, but they can also make your code more complex and lead to unexpected results if not used carefully.

Frequently Asked Questions

Can I reuse a Java Stream after a terminal operation?

No, you can't reuse a Java Stream after a terminal operation has been applied. Once a terminal operation runs, the stream is considered consumed and closed. If you need to process the same data again, you'll need to create a new stream from your data source.

How do I choose between a sequential and parallel stream?

The choice between using a sequential or parallel stream depends on the context. Sequential streams are straightforward and suitable for less complex or smaller datasets. Parallel streams can speed up processing for large datasets but may introduce complexity and overhead. It's often best to start with a sequential stream and consider parallelism only if you're dealing with a significant amount of data and have identified a performance bottleneck.

Are streams better than loops?

Streams offer a more declarative and often more readable approach to data processing compared to traditional loops. They can lead to less code and fewer opportunities for errors. However, loops might still be preferable in scenarios where you need more control over the processing or when working with very simple cases where the overhead of streams isn't justified. The best choice depends on the specific needs of your task and your personal or team's coding preferences.

Conclusion

Java streams are a powerful feature that can make working with collections of data more manageable, readable, and efficient. By understanding and utilizing streams, you can perform complex data processing tasks with less code, reducing the chance of errors and improving the readability of your code. Remember, streams work by taking a source of data and carrying it through a series of operations, ultimately producing a result without the need for manual iteration using loops.

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