What are lambda expressions in Java and what role do they play?

Lambda expressions in Java are anonymous functions that allow passing code as data.

The role of lambda expressions:

• Simplification of code: They enable writing more concise and readable code, especially when working with functional interfaces.
• Functional programming: They support the paradigm of functional programming in Java, making it more flexible.
• Improved collection handling: Used in Stream API for operations like filtering, mapping, and reduction.
• Reduction of boilerplate code: They replace anonymous inner classes in many cases.

Example:

// Using an anonymous inner class
Runnable classicRunnable = new Runnable() {
    @Override
    public void run() {
        System.out.println("Hello from old way!");
    }
};

// Using a lambda expression
Runnable lambdaRunnable = () -> System.out.println("Hello from lambda!");

// Using a lambda with Stream API for filtering
List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
List<String> filteredNames = names.stream()
                                  .filter(name -> name.startsWith("A"))
                                  .collect(Collectors.toList());