Lambda expressions

Definition

A lambda is a short piece of code you can pass around, written (input) -> result. It replaces a bulky anonymous class when an interface has just one method.

Example code

Sorting with a lambda instead of an anonymous class

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

class Demo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>(List.of("Ravi", "Asha", "Meera", "Jo"));

        // the lambda is the "how to compare" code, passed like a value
        names.sort((a, b) -> a.length() - b.length());
        System.out.println(names);

        Runnable greeting = () -> System.out.println("Hello from a lambda");
        greeting.run();

        Comparator<String> alphabetical = (a, b) -> a.compareTo(b);
        names.sort(alphabetical);
        System.out.println(names);
    }
}

// Output:
// [Jo, Ravi, Asha, Meera]
// Hello from a lambda
// [Asha, Jo, Meera, Ravi]