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      1 /*
      2  *  Licensed to the Apache Software Foundation (ASF) under one or more
      3  *  contributor license agreements.  See the NOTICE file distributed with
      4  *  this work for additional information regarding copyright ownership.
      5  *  The ASF licenses this file to You under the Apache License, Version 2.0
      6  *  (the "License"); you may not use this file except in compliance with
      7  *  the License.  You may obtain a copy of the License at
      8  *
      9  *     http://www.apache.org/licenses/LICENSE-2.0
     10  *
     11  *  Unless required by applicable law or agreed to in writing, software
     12  *  distributed under the License is distributed on an "AS IS" BASIS,
     13  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14  *  See the License for the specific language governing permissions and
     15  *  limitations under the License.
     16  */
     17 
     18 package java.util;
     19 
     20 /**
     21  * The {@code TimerTask} class represents a task to run at a specified time. The task
     22  * may be run once or repeatedly.
     23  *
     24  * @see Timer
     25  * @see java.lang.Object#wait(long)
     26  */
     27 public abstract class TimerTask implements Runnable {
     28     /* Lock object for synchronization. It's also used by Timer class. */
     29     final Object lock = new Object();
     30 
     31     /* If timer was cancelled */
     32     boolean cancelled;
     33 
     34     /* Slots used by Timer */
     35     long when;
     36 
     37     long period;
     38 
     39     boolean fixedRate;
     40 
     41     /*
     42      * The time when task will be executed, or the time when task was launched
     43      * if this is task in progress.
     44      */
     45     private long scheduledTime;
     46 
     47     /*
     48      * Method called from the Timer for synchronized getting of when field.
     49      */
     50     long getWhen() {
     51         synchronized (lock) {
     52             return when;
     53         }
     54     }
     55 
     56     /*
     57      * Method called from the Timer object when scheduling an event @param time
     58      */
     59     void setScheduledTime(long time) {
     60         synchronized (lock) {
     61             scheduledTime = time;
     62         }
     63     }
     64 
     65     /*
     66      * Is TimerTask scheduled into any timer?
     67      *
     68      * @return {@code true} if the timer task is scheduled, {@code false}
     69      * otherwise.
     70      */
     71     boolean isScheduled() {
     72         synchronized (lock) {
     73             return when > 0 || scheduledTime > 0;
     74         }
     75     }
     76 
     77     /**
     78      * Creates a new {@code TimerTask}.
     79      */
     80     protected TimerTask() {
     81     }
     82 
     83     /**
     84      * Cancels the {@code TimerTask} and removes it from the {@code Timer}'s queue. Generally, it
     85      * returns {@code false} if the call did not prevent a {@code TimerTask} from running at
     86      * least once. Subsequent calls have no effect.
     87      *
     88      * @return {@code true} if the call prevented a scheduled execution
     89      *         from taking place, {@code false} otherwise.
     90      */
     91     public boolean cancel() {
     92         synchronized (lock) {
     93             boolean willRun = !cancelled && when > 0;
     94             cancelled = true;
     95             return willRun;
     96         }
     97     }
     98 
     99     /**
    100      * Returns the scheduled execution time. If the task execution is in
    101      * progress it returns the execution time of the ongoing task. Tasks which
    102      * have not yet run return an undefined value.
    103      *
    104      * @return the most recent execution time.
    105      */
    106     public long scheduledExecutionTime() {
    107         synchronized (lock) {
    108             return scheduledTime;
    109         }
    110     }
    111 
    112     /**
    113      * The task to run should be specified in the implementation of the {@code run()}
    114      * method.
    115      */
    116     public abstract void run();
    117 
    118 }
    119