Lambdas and Functional Interfaces

Java has supported the functional programming paradigm since version 8.

Functional Interfaces

A functional interface is an interface that has exactly one abstract method. They are usually marked with @FunctionalInterface.

@FunctionalInterface
public interface Operacion {
    int ejecutar(int a, int b);
}

Lambda Expressions

Lambdas are a concise way to implement a functional interface without creating a full class.

Syntax: (parameters) -> expression

// Example of a lambda for adding
Operacion suma = (a, b) -> a + b;
System.out.println(suma.ejecutar(5, 3)); // 8

Stream API and Applications

Lambdas are very powerful when used with collections:

• forEach: Iterates over elements.
• filter: Filters elements based on a condition.
• map: Transforms elements.
• anyMatch / allMatch: Checks conditions.

Example:

List<Integer> numeros = Arrays.asList(1, 2, 3, 4, 5, 6);
List<Integer> pares = numeros.stream()
    .filter(n -> n % 2 == 0)
    .collect(Collectors.toList());
// Result: [2, 4, 6]