Demonstrates the time taken for first invocation of a Java8 lambda

Main.java

import java.util.function.Supplier;


/**
 *  An example that shows the time taken to invoke a Lambda for the first time.
 */
public class Main
{
    public static void main(String[] argv)
    throws Exception
    {
        long start = System.currentTimeMillis();

// uncomment one of these
//        retryLoop(50, 250);
//        retryLambda(50, 250, () -> doSomething());

        long elapsed = System.currentTimeMillis() - start;
        System.out.println("elapsed = " + elapsed);
    }


    public static String retryLoop(long interval, long timeout) throws Exception
    {
        long timeoutAt = System.currentTimeMillis() + timeout;
        while (System.currentTimeMillis() < timeoutAt)
        {
            String value = doSomething();
            if (value != null)
                return value;
            Thread.sleep(interval);
        }

        return null;
    }


    public static String retryLambda(long interval, long timeout, Supplier<String> lambda) throws Exception
    {
        long timeoutAt = System.currentTimeMillis() + timeout;
        while (System.currentTimeMillis() < timeoutAt)
        {
            String value = lambda.get();
            if (value != null)
                return value;
            Thread.sleep(interval);
        }

        return null;
    }


    public static String doSomething()
    {
        return "it doesn't matter what I return";
    }
}