Lambda Expressions in Java

// General forms:
// (parameters) -> expression
// (parameters) -> { statements; }

// No parameters
Runnable r = () -> System.out.println("Running!");

// One parameter (parentheses optional for a single param)
Consumer<String> printer = s -> System.out.println(s);

// Multiple parameters
Comparator<String> byLength = (a, b) -> a.length() - b.length();

// Block body with multiple statements
Runnable task = () -> {
    System.out.println("Step 1");
    System.out.println("Step 2");
};

// Custom functional interface
@FunctionalInterface
interface Calculator {
    int operate(int a, int b);
}
Calculator add = (a, b) -> a + b;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;

public class LambdaDemo {

    @FunctionalInterface
    interface Calculator {
        int operate(int a, int b);
    }

    public static void main(String[] args) {
        // Custom functional interface with a lambda
        Calculator add = (a, b) -> a + b;
        Calculator multiply = (a, b) -> a * b;
        System.out.println("Sum: " + add.operate(3, 4));
        System.out.println("Product: " + multiply.operate(3, 4));

        // Built-in functional interface: Predicate
        Predicate<Integer> isEven = n -> n % 2 == 0;
        System.out.println("Is 10 even? " + isEven.test(10));

        // Comparator with a lambda, used to sort a list
        List<String> names = Arrays.asList("Charlie", "Amy", "Bob");
        names.sort((s1, s2) -> s1.compareTo(s2));
        System.out.println(names);

        // Runnable with a lambda
        Runnable greet = () -> System.out.println("Hello from a lambda thread task!");
        greet.run();
    }
}

Sum: 7
Product: 12
Is 10 even? true
[Amy, Bob, Charlie]
Hello from a lambda thread task!