Added more to readme and javadoc.

README.md

@@ -1,2 +1,22 @@
 # Simply Scheduled
-Lightweight Cron-Like Scheduling Library for Java
+
+This is a very simple cron-like mechanism for scheduling tasks to execute at scheduled points in time. Here's an example:
+
+```java
+Runnable job = () -> System.out.println("Doing some work...");
+Schedule schedule = new RepeatingSchedule(ChronoUnit.SECONDS, 5);
+Scheduler scheduler = new BasicScheduler();
+scheduler.add(new Task(job, schedule));
+scheduler.start();
+```
+> In the above example, we create a new job that simply prints a string to standard output. We create a schedule that repeats the task every 5 seconds. Finally, we add the job and schedule together as a Task, add that task to a scheduler, and start the scheduler.
+
+Besides the `RepeatingSchedule`, this module also includes the following pre-made schedule implementations:
+
+* `DailySchedule` - Executes a task once per day, at a specified time.
+* `HourlySchedule` - Executes a task once per hour, at a specified minute of the hour.
+* `MinutelySchedule` - Executes a task once per minute, at a specified second.
+
+## Extensibility
+
+It is very simple to provide your own custom Schedule implementation if you want a more specific, fine-tuned schedule than what is provided here. Furthermore, you can also provide your own Scheduler implementation, if you prefer to use a different mechanism than the default dynamic thread pool executor service.

src/main/java/nl/andrewlalis/simply_scheduled/BasicScheduler.java

@@ -40,11 +40,12 @@ public class BasicScheduler extends Thread implements Scheduler {
 			try {
 				Task nextTask = this.tasks.take();
 				Instant now = this.clock.instant();
-				long waitTime = nextTask.getSchedule().computeNextExecutionTime(now).toEpochMilli() - now.toEpochMilli();
+				long waitTime = nextTask.getSchedule().getNextExecutionTime(now).toEpochMilli() - now.toEpochMilli();
 				if (waitTime > 0) {
 					Thread.sleep(waitTime);
 				}
 				this.executorService.execute(nextTask.getRunnable());
+				nextTask.getSchedule().markExecuted(this.clock.instant());
 				this.tasks.put(nextTask); // Put the task back in the queue.
 			} catch (InterruptedException e) {
 				this.setRunning(false);

src/main/java/nl/andrewlalis/simply_scheduled/schedule/DailySchedule.java

@@ -2,6 +2,10 @@ package nl.andrewlalis.simply_scheduled.schedule;
 
 import java.time.*;
 
+/**
+ * A daily schedule plans for the execution of a task once per day, at a
+ * specified local time.
+ */
 public class DailySchedule implements Schedule {
 	private final ZoneId zoneId;
 	private final LocalTime time;
@@ -16,7 +20,7 @@ public class DailySchedule implements Schedule {
 	}
 
 	@Override
-	public Instant computeNextExecutionTime(Instant referenceInstant) {
+	public Instant getNextExecutionTime(Instant referenceInstant) {
 		ZonedDateTime currentTime = referenceInstant.atZone(this.zoneId);
 		LocalDate currentDay = LocalDate.from(referenceInstant);
 		ZonedDateTime sameDayExecution = currentDay.atTime(this.time).atZone(this.zoneId);

src/main/java/nl/andrewlalis/simply_scheduled/schedule/HourlySchedule.java

@@ -5,6 +5,10 @@ import java.time.ZoneId;
 import java.time.ZonedDateTime;
 import java.time.temporal.ChronoUnit;
 
+/**
+ * An hourly schedule is used to execute a task once per hour, at a specific
+ * minute of the hour.
+ */
 public class HourlySchedule implements Schedule {
 	private final ZoneId zoneId;
 	private final int minute;
@@ -22,7 +26,7 @@ public class HourlySchedule implements Schedule {
 	}
 
 	@Override
-	public Instant computeNextExecutionTime(Instant referenceInstant) {
+	public Instant getNextExecutionTime(Instant referenceInstant) {
 		ZonedDateTime currentTime = referenceInstant.atZone(this.zoneId);
 		int currentMinute = currentTime.getMinute();
 		if (currentMinute < this.minute) {

src/main/java/nl/andrewlalis/simply_scheduled/schedule/MinutelySchedule.java

@@ -20,7 +20,7 @@ public class MinutelySchedule implements Schedule {
 	}
 
 	@Override
-	public Instant computeNextExecutionTime(Instant referenceInstant) {
+	public Instant getNextExecutionTime(Instant referenceInstant) {
 		ZonedDateTime currentTime = referenceInstant.atZone(this.zoneId);
 		int currentSecond = currentTime.getSecond();
 		if (currentSecond >= this.second) {

src/main/java/nl/andrewlalis/simply_scheduled/schedule/RepeatingSchedule.java

@@ -30,12 +30,15 @@ public class RepeatingSchedule implements Schedule {
 	 * @return The next instant to execute the task at.
 	 */
 	@Override
-	public Instant computeNextExecutionTime(Instant referenceInstant) {
+	public Instant getNextExecutionTime(Instant referenceInstant) {
 		if (this.lastExecution == null) {
 			this.lastExecution = referenceInstant;
 		}
-		Instant nextExecution = this.lastExecution.plus(multiple, unit);
-		this.lastExecution = nextExecution;
-		return nextExecution;
+		return this.lastExecution.plus(multiple, unit);
+	}
+
+	@Override
+	public void markExecuted(Instant instant) {
+		this.lastExecution = instant;
 	}
 }

src/main/java/nl/andrewlalis/simply_scheduled/schedule/Schedule.java

@@ -14,14 +14,18 @@ public interface Schedule {
 	 * produce an instant sometime in the future at which the next execution of
 	 * a task should happen.
 	 *
-	 * <p>
-	 *     <strong>Note that certain implementations may introduce side-effects
-	 *     when this method is called more than once.</strong>
-	 * </p>
-	 *
 	 * @param referenceInstant The instant representing the current time.
 	 * @return An instant in the future indicating the next time at which a task
 	 * using this schedule should be executed.
 	 */
-	Instant computeNextExecutionTime(Instant referenceInstant);
+	Instant getNextExecutionTime(Instant referenceInstant);
+
+	/**
+	 * This method is called on the schedule as an indication that the scheduler
+	 * should move on to planning the next execution time.
+	 * @param instant The instant at which the schedule's task(s) were executed.
+	 */
+	default void markExecuted(Instant instant) {
+		// Default no-op.
+	}
 }

src/main/java/nl/andrewlalis/simply_scheduled/schedule/Task.java

@@ -34,6 +34,6 @@ public class Task implements Comparable<Task>{
 	@Override
 	public int compareTo(Task o) {
 		Instant now = clock.instant();
-		return this.schedule.computeNextExecutionTime(now).compareTo(o.getSchedule().computeNextExecutionTime(now));
+		return this.schedule.getNextExecutionTime(now).compareTo(o.getSchedule().getNextExecutionTime(now));
 	}
 }

src/test/java/nl/andrewlalis/simply_scheduled/SchedulerTest.java

@@ -31,7 +31,7 @@ public class SchedulerTest {
 		scheduler.addTask(task);
 		scheduler.start();
 		System.out.println("Now: " + clock.instant().toString());
-		System.out.println("Next task execution: " + task.getSchedule().computeNextExecutionTime(clock.instant()));
+		System.out.println("Next task execution: " + task.getSchedule().getNextExecutionTime(clock.instant()));
 		System.out.printf("Waiting %d seconds for task to run...", secondsLeft);
 		assertFalse(flag.get());
 		try {