Java Functional Programming Techniques

1. Introduction

Functional programming in Java is a programming paradigm that treats computation as the evaluation of mathematical functions. It avoids changing state and mutable data, focusing instead on the use of functions as first-class citizens.

2. Key Concepts

• First-Class Functions: Functions are treated like any other variable.
• Higher-Order Functions: Functions that take other functions as parameters or return them.
• Immutability: Once created, data cannot be changed.
• Function Composition: Combining simple functions to build more complex ones.

3. Lambda Expressions

Lambda expressions are a key feature in Java 8 that allows you to create anonymous functions. They enable you to write concise and readable code for functional interfaces.

Runnable runnable = () -> System.out.println("Hello, World!");
runnable.run();

In the above example, a Runnable interface is implemented using a lambda expression.

4. Streams API

The Streams API is a powerful feature introduced in Java 8 that allows you to process collections of objects in a functional way.

List names = Arrays.asList("John", "Jane", "Jack");
List filteredNames = names.stream()
    .filter(name -> name.startsWith("J"))
    .collect(Collectors.toList());

System.out.println(filteredNames); // Output: [John, Jane, Jack]

This code filters names that start with "J" using the Streams API.

5. Optional Class

The Optional class is a container object which may or may not contain a value. It is used to avoid null references and NullPointerExceptions.

Optional optionalName = Optional.ofNullable(getName());
optionalName.ifPresent(name -> System.out.println("Name: " + name));

In this example, the name is printed only if it is present.

6. Best Practices

• Use lambda expressions for concise code when working with functional interfaces.
• Prefer using streams for bulk data operations over traditional loops.
• Utilize the Optional class to handle nullable values gracefully.
• Avoid side effects in functions to maintain immutability.

7. FAQ