Stream API and Lambda Integration in Java

1. Introduction

Java 8 introduced two powerful features: the Stream API and Lambda expressions. These features allow developers to process collections of objects in a functional style, making code more concise and easier to read.

2. Key Concepts

• Stream: A sequence of elements supporting sequential and parallel aggregate operations.
• Lambda Expression: A concise way to represent a functional interface using an expression.
• Functional Interface: An interface with a single abstract method.

3. Stream API

The Stream API allows for functional-style operations on streams of elements, such as map, filter, and reduce. Here are some common operations:

• map: Transforms each element in the stream.
• filter: Filters elements based on a given predicate.
• reduce: Combines elements to produce a single result.

Example of using Stream API:

List names = Arrays.asList("Alice", "Bob", "Charlie");
List filteredNames = names.stream()
    .filter(name -> name.startsWith("A"))
    .collect(Collectors.toList());
System.out.println(filteredNames); // Output: [Alice]

4. Lambda Expressions

Lambda expressions provide a clear and concise way to represent a one-method interface using an expression. The syntax is as follows:

(parameters) -> expression

Example of a Lambda expression:

Runnable runnable = () -> System.out.println("Running in a thread");
new Thread(runnable).start();

5. Integration of Stream API and Lambda

Combining the Stream API with Lambda expressions is where the real power lies. You can use Lambda expressions to specify the operations performed on the elements of a stream.

Example:

List numbers = Arrays.asList(1, 2, 3, 4, 5);
int sum = numbers.stream()
    .filter(n -> n % 2 == 0) // Filter even numbers
    .mapToInt(n -> n) // Map to int
    .sum(); // Sum them up
System.out.println(sum); // Output: 6

6. Best Practices

• Use parallel streams for large datasets to improve performance.
• Prefer method references over Lambda expressions when possible for clarity.
• Avoid side effects in Lambda expressions to ensure predictability.

7. FAQ