App04-async-request-supplyAsync.java

import java.util.concurrent.*;
import java.util.*;

class App{

    public static void main(String [] args) throws Exception{
    
        // Sync request 
        //
        // calculatePrice("bag");
        // calculatePrice("tablet");
        
        // Async request 
        //
        Future<Double> req1 = getPriceAsync("bag");
        Future<Double> req2 = getPriceAsync("tablet");
        
        System.out.println(req1.get());
        System.out.println(req2.get());
    }
    
    private static Future<Double> getPriceAsync(String product) { 
        return CompletableFuture.supplyAsync(() -> {
                System.out.println("Requesting...");
                return calculatePrice(product);
        });

    }
    
    private static double calculatePrice(String product) { 
        delay();
        double res = random.nextDouble() * product.charAt(0) + product.charAt(1);
        return ((int) (res * 100)) / ((double) 100);
    }
    
    private static void delay() {
        try {
            Thread.sleep(3000L);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
    private static final Random random = new Random();
    
    
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    /****************************************************************/
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    
    public static long measurePerformance(Runnable action){
        long fastest = Long.MAX_VALUE;
        for (int i = 0; i < 1; i++) {
            long start = System.nanoTime();
            action.run();
            long duration = (System.nanoTime() - start) / 1_000_000;
            System.out.println(duration + " ms");
            if (duration < fastest) fastest = duration;
        }
        return fastest;
    }
}