Stream API in Java

The Stream API is a powerful feature introduced in Java 8 that allows for functional-style operations on sequences of elements, such as collections. It provides a way to process data in a more expressive and concise manner compared to traditional iterative approaches. Here's a breakdown of its purpose, use cases, and advantages

What is Stream API?

• Streams: A stream is a sequence of elements that can be processed in parallel or sequentially. It does not store elements; instead, it operates on data from a source (like a collection, array, or I/O channel).
• Functional Operations: Stream operations are usually chained together and are either intermediate (like map, filter, and sorted) or terminal (like collect, forEach, and reduce).

Why Use Stream API?

1. Conciseness: Stream operations often require less code than traditional loops, making the code easier to read and maintain.
2. Functional Programming: It encourages a functional programming style, allowing you to write cleaner code by using lambdas and method references.
3. Parallel Processing: Streams can easily be parallelized with minimal changes to your code (using parallelStream()), which can lead to performance improvements in multi-core environments.
4. Lazy Evaluation: Streams are lazy; operations are not executed until a terminal operation is called. This can lead to performance optimizations.

Where to Use Stream API?

1. Data Transformation: When you need to transform collections, such as converting a list of objects into a list of their properties.
2. Filtering Data: For selecting specific elements from a collection based on conditions.
3. Aggregating Data: When you need to calculate aggregates like sums, averages, or counts.
4. Sorting Collections: Stream API can be used to sort elements in a collection in a concise manner.
5. Working with I/O: You can also use streams for processing data from files or network sources.

Example Usage

Here’s a simple example that demonstrates several Stream operations:

package com.example.demo.test;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class StreamExample {
	public static void main(String[] args) {
		List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "Diana");
		// Filter, transform, and collect
		List<String> filteredNames = names.stream().filter(name ->     name.startsWith("A")).map(String::toUpperCase)
				.collect(Collectors.toList());
		System.out.println(filteredNames);
	}
}        

output-

[ALICE]        

In this example, we filter names that start with 'A', transform them to uppercase, and collect the results into a list. This showcases the expressiveness and clarity of the Stream API.