package com.zetcode;

import java.util.Random;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.TimeUnit;

import java.util.function.Function;

import java.util.function.Supplier;

public class TheyApply {

// A random supplier that sleeps for a second, and then returns

// a random value

public static class RandomSupplier implements Supplier<Integer> {

@Override

public Integer get() {

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

return new Random().nextInt(10);

}

}

// A (pure) function that adds one to a given Integer

public static class AddOne implements Function<Integer, Integer> {

@Override

public Integer apply(Integer x) {

return x + 1;

}

}

public static void main(String[] args) throws Exception {

ExecutorService exec = Executors.newSingleThreadExecutor();

CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new RandomSupplier(), exec);

System.out.println(future.isDone()); // false

CompletableFuture<Integer> f2 = future.thenApply(new AddOne());

System.out.println(f2.get()); // Waits until the "calculation" is done and prints the result

exec.shutdown();

try {

if (!exec.awaitTermination(4, TimeUnit.SECONDS)) {

exec.shutdownNow();

}

} catch (InterruptedException e) {

exec.shutdownNow();

}

}

}