File	Doc	Category	Size	Date	Package
Timer.java	API Doc	Java SE 6 API	27685	Tue Jun 10 00:25:56 BST 2008	java.util

Timer

• java.lang.Object

Fields Summary
private TaskQueue	queue The timer task queue. This data structure is shared with the timer thread. The timer produces tasks, via its various schedule calls, and the timer thread consumes, executing timer tasks as appropriate, and removing them from the queue when they're obsolete.
private TimerThread	thread The timer thread.
private Object	threadReaper This object causes the timer's task execution thread to exit gracefully when there are no live references to the Timer object and no tasks in the timer queue. It is used in preference to a finalizer on Timer as such a finalizer would be susceptible to a subclass's finalizer forgetting to call it.
private static int	nextSerialNumber This ID is used to generate thread names. (It could be replaced by an AtomicInteger as soon as they become available.)

Constructors Summary
public Timer() Creates a new timer. The associated thread does not run as a daemon. see Thread see #cancel() this("Timer-" + serialNumber());
public Timer(boolean isDaemon) Creates a new timer whose associated thread may be specified to run as a daemon. A daemon thread is called for if the timer will be used to schedule repeating "maintenance activities", which must be performed as long as the application is running, but should not prolong the lifetime of the application. param isDaemon true if the associated thread should run as a daemon. see Thread see #cancel() this("Timer-" + serialNumber(), isDaemon);
public Timer(String name) Creates a new timer whose associated thread has the specified name. The associated thread does not run as a daemon. param name the name of the associated thread throws NullPointerException if name is null see Thread#getName() see Thread#isDaemon() since 1.5 thread.setName(name); thread.start();
public Timer(String name, boolean isDaemon) Creates a new timer whose associated thread has the specified name, and may be specified to run as a daemon. param name the name of the associated thread param isDaemon true if the associated thread should run as a daemon throws NullPointerException if name is null see Thread#getName() see Thread#isDaemon() since 1.5 thread.setName(name); thread.setDaemon(isDaemon); thread.start();

Methods Summary
public void	cancel() Terminates this timer, discarding any currently scheduled tasks. Does not interfere with a currently executing task (if it exists). Once a timer has been terminated, its execution thread terminates gracefully, and no more tasks may be scheduled on it. Note that calling this method from within the run method of a timer task that was invoked by this timer absolutely guarantees that the ongoing task execution is the last task execution that will ever be performed by this timer. This method may be called repeatedly; the second and subsequent calls have no effect. synchronized(queue) { thread.newTasksMayBeScheduled = false; queue.clear(); queue.notify(); // In case queue was already empty. }
public int	purge() Removes all cancelled tasks from this timer's task queue. Calling this method has no effect on the behavior of the timer, but eliminates the references to the cancelled tasks from the queue. If there are no external references to these tasks, they become eligible for garbage collection. Most programs will have no need to call this method. It is designed for use by the rare application that cancels a large number of tasks. Calling this method trades time for space: the runtime of the method may be proportional to n + c log n, where n is the number of tasks in the queue and c is the number of cancelled tasks. Note that it is permissible to call this method from within a a task scheduled on this timer. return the number of tasks removed from the queue. since 1.5 int result = 0; synchronized(queue) { for (int i = queue.size(); i > 0; i--) { if (queue.get(i).state == TimerTask.CANCELLED) { queue.quickRemove(i); result++; } } if (result != 0) queue.heapify(); } return result;
private void	sched(java.util.TimerTask task, long time, long period) Schedule the specified timer task for execution at the specified time with the specified period, in milliseconds. If period is positive, the task is scheduled for repeated execution; if period is zero, the task is scheduled for one-time execution. Time is specified in Date.getTime() format. This method checks timer state, task state, and initial execution time, but not period. throws IllegalArgumentException if time() is negative. throws IllegalStateException if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. if (time < 0) throw new IllegalArgumentException("Illegal execution time."); synchronized(queue) { if (!thread.newTasksMayBeScheduled) throw new IllegalStateException("Timer already cancelled."); synchronized(task.lock) { if (task.state != TimerTask.VIRGIN) throw new IllegalStateException( "Task already scheduled or cancelled"); task.nextExecutionTime = time; task.period = period; task.state = TimerTask.SCHEDULED; } queue.add(task); if (queue.getMin() == task) queue.notify(); }
public void	schedule(java.util.TimerTask task, long delay) Schedules the specified task for execution after the specified delay. param task task to be scheduled. param delay delay in milliseconds before task is to be executed. throws IllegalArgumentException if delay is negative, or delay + System.currentTimeMillis() is negative. throws IllegalStateException if task was already scheduled or cancelled, or timer was cancelled. if (delay < 0) throw new IllegalArgumentException("Negative delay."); sched(task, System.currentTimeMillis()+delay, 0);
public void	schedule(java.util.TimerTask task, java.util.Date time) Schedules the specified task for execution at the specified time. If the time is in the past, the task is scheduled for immediate execution. param task task to be scheduled. param time time at which task is to be executed. throws IllegalArgumentException if time.getTime() is negative. throws IllegalStateException if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. sched(task, time.getTime(), 0);
public void	schedule(java.util.TimerTask task, long delay, long period) Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals separated by the specified period. In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution. If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well. In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate). Fixed-delay execution is appropriate for recurring activities that require "smoothness." In other words, it is appropriate for activities where it is more important to keep the frequency accurate in the short run than in the long run. This includes most animation tasks, such as blinking a cursor at regular intervals. It also includes tasks wherein regular activity is performed in response to human input, such as automatically repeating a character as long as a key is held down. param task task to be scheduled. param delay delay in milliseconds before task is to be executed. param period time in milliseconds between successive task executions. throws IllegalArgumentException if delay is negative, or delay + System.currentTimeMillis() is negative. throws IllegalStateException if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. if (delay < 0) throw new IllegalArgumentException("Negative delay."); if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, System.currentTimeMillis()+delay, -period);
public void	schedule(java.util.TimerTask task, java.util.Date firstTime, long period) Schedules the specified task for repeated fixed-delay execution, beginning at the specified time. Subsequent executions take place at approximately regular intervals, separated by the specified period. In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution. If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well. In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate). Fixed-delay execution is appropriate for recurring activities that require "smoothness." In other words, it is appropriate for activities where it is more important to keep the frequency accurate in the short run than in the long run. This includes most animation tasks, such as blinking a cursor at regular intervals. It also includes tasks wherein regular activity is performed in response to human input, such as automatically repeating a character as long as a key is held down. param task task to be scheduled. param firstTime First time at which task is to be executed. param period time in milliseconds between successive task executions. throws IllegalArgumentException if time.getTime() is negative. throws IllegalStateException if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, firstTime.getTime(), -period);
public void	scheduleAtFixedRate(java.util.TimerTask task, long delay, long period) Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals, separated by the specified period. In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate). Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another. param task task to be scheduled. param delay delay in milliseconds before task is to be executed. param period time in milliseconds between successive task executions. throws IllegalArgumentException if delay is negative, or delay + System.currentTimeMillis() is negative. throws IllegalStateException if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. if (delay < 0) throw new IllegalArgumentException("Negative delay."); if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, System.currentTimeMillis()+delay, period);
public void	scheduleAtFixedRate(java.util.TimerTask task, java.util.Date firstTime, long period) Schedules the specified task for repeated fixed-rate execution, beginning at the specified time. Subsequent executions take place at approximately regular intervals, separated by the specified period. In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate). Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another. param task task to be scheduled. param firstTime First time at which task is to be executed. param period time in milliseconds between successive task executions. throws IllegalArgumentException if time.getTime() is negative. throws IllegalStateException if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, firstTime.getTime(), period);
private static synchronized int	serialNumber() return nextSerialNumber++;