What are lambda expressions in Java?

A lambda expression in Java is an anonymous function that allows you to pass blocks of code as objects. It provides a concise way to implement functional interfaces (interfaces with a single abstract method).

Syntax of a lambda expression:

• List of parameters (can be empty).
• The -> operator.
• Expression body (can be an expression or a block of statements).

Examples:

// Lambda for the functional interface Runnable
Runnable task = () -> System.out.println("Hello from lambda!");

// Lambda for the functional interface Comparator<Integer>
Comparator<Integer> comparator = (a, b) -> a.compareTo(b);

// Lambda with a block of statements
Consumer<String> greeter = name -> {
    String message = "Hello, " + name + "!";
    System.out.println(message);
};

Key features:

• Anonymity: they have no name.
• Functional interfaces: used to implement functional interfaces.
• Conciseness: allow writing more compact code compared to anonymous classes.
• Variable capture: can capture effectively final local variables from the surrounding context.

Using lambda expressions improves code readability and simplifies working with APIs oriented towards functional programming, such as the Stream API.