Java Lambda Expressions, Method References & Functional Interfaces
Master Java lambda syntax: functional interfaces (@FunctionalInterface), Predicate, Function, Consumer, Supplier, and lexical scoping.
Java
import java.util.function.Predicate;
import java.util.function.Function;
public class LambdaGuide {
public static void main(String[] args) {
// Predicate: takes an input and returns a boolean
Predicate<String> isValidPhone = phone -> phone != null && phone.matches("\\d{10}");
System.out.println("Valid phone: " + isValidPhone.test("7503962162"));
// Function: takes T and returns R
Function<String, Integer> stringLength = String::length;
System.out.println("Length: " + stringLength.apply("Ghaziabad"));
}
}1. What is a Lambda Expression?
A lambda expression is an anonymous block of code that provides an implementation of a Single Abstract Method (SAM) interface, commonly known as a Functional Interface. Introduced in Java 8, lambdas eliminate verbose anonymous inner classes.
2. Core Built-in Functional Interfaces
Java provides standard functional interfaces in java.util.function:
Predicate<T>:boolean test(T t)for filtering conditions.Function<T, R>:R apply(T t)for mapping and transforming data.Consumer<T>:void accept(T t)for operations with side effects.Supplier<T>:T get()for deferred value generation.
Key Engineering Takeaways
- Functional interfaces are marked with @FunctionalInterface.
- Lambdas can capture effectively final variables from enclosing lexical scopes.
- Method references provide clean shorthand syntax when a lambda simply forwards parameters to an existing method.
Frequently Asked Questions
Can a functional interface have default methods?
Yes! A functional interface can have multiple default and static methods, as long as it has exactly one abstract method.
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