What are lambda expressions in Java and what capabilities do they provide?

A lambda expression in Java is an anonymous function that does not belong to any class and can be passed as an object.

Syntax: (parameters) -> { body }

Capabilities:

1. Functional Interface: A lambda expression can be assigned to a variable of a functional interface type (an interface with a single abstract method).

   // Functional interface  
   @FunctionalInterface  
   interface MyInterface {  
       void myMethod();  
   }  
   
   // Using lambda expression  
   MyInterface lambda = () -> System.out.println("Hello from lambda!");  
   lambda.myMethod();  
   

2. Simplification of code writing: Replaces anonymous inner classes for implementing functional interfaces.

   // Before Java 8 (anonymous class)  
   Thread thread1 = new Thread(new Runnable() {  
       @Override  
       public void run() {  
           System.out.println("Old way");  
       }  
   });  
   
   // From Java 8 (lambda)  
   Thread thread2 = new Thread(() -> System.out.println("Lambda way"));  
   

3. Using in Stream API: Integrated with Stream API for performing operations on collections.

   List<String> names = Arrays.asList("Alice", "Bob", "Charlie");  
   names.stream()  
        .filter(name -> name.startsWith("A")) // Lambda expression  
        .forEach(System.out::println);        // Method reference lambda  
   

4. Deferred execution: Code inside the lambda expression executes only when the functional method is called.
5. Scope of variables: Lambda expressions can capture variables from the outer scope (local variables must be final or effectively final).

Advantage	Description
Conciseness of code	Reduces "verbosity" compared to anonymous classes.
Improved readability	Code becomes more concise and understandable.
Parallel processing	Supported by Stream API for parallel operations.