java.util.Timer Maven / Gradle / Ivy

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This work corresponds to the API signatures of JSR 219: Foundation Profile 1.1. In the event of a discrepency between this work and the JSR 219 specification, which is available at http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence. */ package java.util; import java.util.Date; /** * A facility for threads to schedule tasks for future execution in a * background thread. Tasks may be scheduled for one-time execution, or for * repeated execution at regular intervals. * *

Corresponding to each Timer object is a single background * thread that is used to execute all of the timer's tasks, sequentially. * Timer tasks should complete quickly. If a timer task takes excessive time * to complete, it "hogs" the timer's task execution thread. This can, in * turn, delay the execution of subsequent tasks, which may "bunch up" and * execute in rapid succession when (and if) the offending task finally * completes. * *

After the last live reference to a Timer object goes away * and all outstanding tasks have completed execution, the timer's task * execution thread terminates gracefully (and becomes subject to garbage * collection). However, this can take arbitrarily long to occur. By * default, the task execution thread does not run as a daemon thread, * so it is capable of keeping an application from terminating. If a caller * wants to terminate a timer's task execution thread rapidly, the caller * should invoke the the timer's cancel method. * *

If the timer's task execution thread terminates unexpectedly, for * example, because its stop method is invoked, any further * attempt to schedule a task on the timer will result in an * IllegalStateException, as if the timer's cancel * method had been invoked. * *

This class is thread-safe: multiple threads can share a single * Timer object without the need for external synchronization. * *

This class does not offer real-time guarantees: it schedules * tasks using the Object.wait(long) method. * *

Implementation note: This class scales to large numbers of concurrently * scheduled tasks (thousands should present no problem). Internally, * it uses a binary heap to represent its task queue, so the cost to schedule * a task is O(log n), where n is the number of concurrently scheduled tasks. * * @author Josh Bloch * @version 1.8, 05/17/00 * @see TimerTask * @see Object#wait(long) * @since 1.3 */ public class Timer { /** * Creates a new timer. The associated thread does not run as * a daemon. * * @see Thread * @see #cancel() */ public Timer() { } /** * Creates a new timer whose associated thread may be specified to * run as a daemon. A deamon 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() */ public Timer(boolean isDaemon) { } /** * 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. */ public void schedule(TimerTask task, long delay) { } /** * 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. */ public void schedule(TimerTask task, java.util.Date time) { } /** * 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. */ public void schedule(TimerTask task, long delay, 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. */ public void schedule(TimerTask task, java.util.Date firstTime, 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 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. */ public void scheduleAtFixedRate(TimerTask task, long delay, 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 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. */ public void scheduleAtFixedRate(TimerTask task, java.util.Date firstTime, long period) { } /** * 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. * *