Timer

Timer

java.util

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Java 1.3

This class implements a timer: its methods allow you to schedule one or more runnable TimerTask objects to be executed (once or repetitively) by a background thread at a specified time in the future. You can create a timer with the Timer( ) constructor. The no-argument version of this constructor creates a regular non-daemon background thread, which means that the Java VM will not terminate while the timer thread is running. Pass true to the constructor if you want the background thread to be a daemon thread. In Java 5.0 you can also specify the name of the background thread when creating a Timer .

Once you have created a Timer , you can schedule TimerTask objects to be run in the future with the various schedule( ) and scheduleAtFixedRate( ) methods. To schedule a task for a single execution, use one of the two-argument schedule( ) methods and specify the desired execution time either as a number of milliseconds in the future or as an absolute Date . If the number of milliseconds is , or if the Date object represents a time already passed, the task is scheduled for immediate execution.

To schedule a repeating task, use one of the three-argument versions of schedule( ) or scheduleAtFixedRate( ) . These methods are passed an argument that specifies the time (either as a number of milliseconds or as a Date object) of the first execution of the task and another argument, period , that specifies the number of milliseconds between repeated executions of the task. The schedule( ) methods schedule the task for fixed-interval execution. That is, each execution is scheduled for period milliseconds after the previous execution ends . Use schedule( ) for tasks such as animation, where it is important to have a relatively constant interval between executions. The scheduleAtFixedRate( ) methods, on the other hand, schedule tasks for fixed-rate execution. That is, each repetition of the task is scheduled for period milliseconds after the previous execution begins . Use scheduleAtFixedRate( ) for tasks, such as updating a clock display, that must occur at specific absolute times rather than at fixed intervals.

A single Timer object can comfortably schedule many TimerTask objects. Note, however, that all tasks scheduled by a single Timer share a single thread. If you are scheduling many rapidly repeating tasks, or if some tasks take a long time to execute, other tasks may have their scheduled executions delayed.

When you are done with a Timer , call cancel( ) to stop its associated thread from running. This is particularly important when you are using a timer whose associated thread is not a daemon thread, because otherwise the timer thread can prevent the Java VM from exiting. To cancel the execution of a particular task, use the cancel( ) method of TimerTask .

 public class  Timer  {  // Public Constructors  public  Timer  ( );        public  Timer  (boolean  isDaemon  );  5.0  public  Timer  (String  name  );  5.0  public  Timer  (String  name  , boolean  isDaemon  );  // Public Instance Methods  public void  cancel  ( );  5.0  public int  purge  ( );        public void  schedule  (TimerTask  task  , long  delay  );        public void  schedule  (TimerTask  task  , Date  time  );        public void  schedule  (TimerTask  task  , long  delay  , long  period  );        public void  schedule  (TimerTask  task  , Date  firstTime  , long  period  );        public void  scheduleAtFixedRate  (TimerTask  task  , long  delay  , long  period  );        public void  scheduleAtFixedRate  (TimerTask  task  , Date  firstTime  , long  period  );   }