Lamdas

Lambdas are a way of using functional programming to develop concise and powerful Java code since Java version 8.

Lambdas implement functional interfaces using the @FunctionalInterface annotation which will contain a single method that allows you to pass functions as data dynamically.

Previously, functions had to be contained in a class.

java.util.function contains a number of useful functional interfaces for writing lambdas by passing in arguments and either outputting something or returning nothing.

Functional interfaces

Consumer

A consumer is a functional interface that accepts an input and does not produce an output.

ArrayList<String> students = new ArrayList<>();
students.add("Naiomi");
students.add("Teyte");
students.add("Myloh");

Consumer<String> printItem = n -> System.out.println(n);
students.forEach(printItem);

Function

A function takes an input and produces an output. An example of this is the stream.map() method.

Function<Integer, Integer> doubly = n -> n + n;
System.out.println(doubly.apply(8));

Supplier

A supplier does not take any inputs but produces an output. It has only one method get() and does not have any default and static methods.

Supplier<Double> randomNumUnder100 = Math.random() * 100;
System.out.println(randomNumUnder100.get());
Supplier<Double> randomNumUnder100 = Math.random() * 100;
System.out.println(randomNumUnder100.get());

Predicate

The predicate interface accepts an argument and returns a boolean value. The filter method of a stream accepts a predicate to filter the data.

IntPredicate isDivByTwo = n -> n / 2 == 0;
System.out.println(isDiveMyTwo(9));

Scenario: Calculate the value of 2 numbers multiplied by each other and then added to a random number

Implement a functional interface

@FunctionalInterface
public interface Calculator {
   int calculate(int x, int y);
}

Implement the calculate method

public static void main(String[] args) {
   Calculator calculator = (x, y) -> {
      Random random = new Random();
      int randomNumber = random.nextInt(50);
      return x * y + randomNumber;
    };

   System.out.println(calculator.calculate(1, 2));
}