This sample demonstates the use of the new Java concurrency API

CurrencyConverter.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class CurrencyConverter {
	final String[] CURRENCY = new String[] { "IDR", "MYR", "AUD", "SGD", "THB" };

	void checkRateSequential() throws Exception {

		System.out.println("checkRateSequential :");
		long start = System.nanoTime();
		for (String ccy : CURRENCY) {
			HashMap ccyRate = getRates(ccy);
			System.out.println("Value of $1 in " + ccy + " is " + ccyRate.get("RATE"));
		}

		long end = System.nanoTime();
		System.out.println("Time (seconds) taken " + (end - start) / 1.0e9);
	}

	void checkRateAllAtEnd() throws Exception {
		System.out.println("checkRateAllAtEnd :");
		long start = System.nanoTime();
		
		List<Callable<HashMap>> tasks = new ArrayList<Callable<HashMap>>();
		for (final String ccy : CURRENCY) {
			tasks.add(new Callable<HashMap>() {
				public HashMap call() throws Exception {
					return getRates(ccy);
				}
			});
		}
		ExecutorService executorPool = Executors.newCachedThreadPool();
		final List<Future<HashMap>> listRates = executorPool.invokeAll(tasks, 3600, TimeUnit.SECONDS);
		
		for (Future<HashMap> rate : listRates) {
			HashMap ccyRate = rate.get();
			System.out.println("Value of $1 in " + ccyRate.get("CCY") + " is " + ccyRate.get("RATE"));
		}
		
		executorPool.shutdown();
		
		long end = System.nanoTime();
		System.out.println("Time (seconds) taken " + (end - start) / 1.0e9);
	}

	void checkRateAsItComplete() throws Exception {
		System.out.println("checkRateAsItComplete :");
		long start = System.nanoTime();
		
		ExecutorService executorPool = Executors.newCachedThreadPool();
		CompletionService<HashMap> compService = new ExecutorCompletionService<HashMap>(executorPool);
		
		for (final String ccy : CURRENCY) {
			compService.submit(new Callable<HashMap>() {
				public HashMap call() throws Exception {
					return getRates(ccy);
				}
			});
		}
		
		
		for (int i=0; i<CURRENCY.length; i++) {
			Future<HashMap> future = compService.take();
			HashMap ccyRate = future.get();
			System.out.println("Value of $1 in " + ccyRate.get("CCY") + " is " + ccyRate.get("RATE"));
		}
		
		executorPool.shutdown();

		long end = System.nanoTime();
		System.out.println("Time (seconds) taken " + (end - start) / 1.0e9);
	}

	private HashMap getRates(String ccy) throws Exception {

		URL url = new URL(
				"http://finance.yahoo.com/d/quotes.csv?e=.csv&f=sl1d1t1&s=USD"
						+ ccy + "=X");
		BufferedReader reader = new BufferedReader(new InputStreamReader(
				url.openStream()));

		String data = reader.readLine();
		String[] dataItems = data.split(",");
		Double rate = Double.valueOf(dataItems[1]);
		HashMap ccyRate = new HashMap();
		ccyRate.put("CCY", ccy);
		ccyRate.put("RATE", rate);

		return ccyRate;
	}
	
	public static void main(String[] args) {
		CurrencyConverter ccyConverter = new CurrencyConverter();
		try {
			ccyConverter.checkRateSequential();
			ccyConverter.checkRateAllAtEnd();
			ccyConverter.checkRateAsItComplete();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}