Java Java.util.Timer用法及代碼示例

Timer 類提供了一個方法調用，線程使用該方法調用來安排任務，例如在某個常規時間點後運行一段代碼。每個任務可以安排運行一次或重複執行多次。每個計時器對象都與一個後台線程關聯，該後台線程負責執行計時器對象的所有任務。
筆記：

• Timer 類是線程安全的。
• Timer 類使用二進製堆數據結構來存儲其任務。

構造函數：

• Timer()：創建一個新的計時器
• 計時器(布爾 isDaemon)：創建一個新的計時器，其關聯的線程可以指定為守護進程運行
• 計時器(字符串名稱)：創建一個新的計時器，其關聯的線程具有指定的名稱
• 計時器(字符串名稱，布爾值 isDaemon)：創建一個新的計時器，其關聯的線程具有指定的名稱，並且可以指定為作為守護進程運行

聲明：

public class Timer
        extends Object

從類 java.lang.Object 繼承的方法

• clone
• equals
• finalize
• getClass
• hashCode
• notify
• notifyAll
• toString
• wait

方法：

• cancel(): java.util.Timer.cancel()終止此計時器，丟棄所有當前計劃的任務。不幹擾當前正在執行的任務(如果存在)。一旦計時器終止，其執行線程就會正常終止，並且不能在其上調度更多任務
  用法：

public void cancel()

• purge(): java.util.Timer.purge()從此計時器的任務隊列中刪除所有已取消的任務
  用法：

public int purge()
返回：
the number of tasks removed from the queue

• 時間表(TimerTask任務，日期時間)：java.util.Timer.schedule(TimerTask任務，日期時間)安排指定的任務在指定的時間執行
  用法：

public void schedule(TimerTask task, Date time)
參數：
task - task to be scheduled.
time - time at which task is to be executed.
Throws:
IllegalArgumentException - if time.getTime() is negative.
IllegalStateException - if the task was already scheduled or cancelled, 
the timer was cancelled, or timer thread terminated.
NullPointerException - if task or time is null

• 時間表(TimerTask任務，日期firstTime，長周期)：java.util.Timer.schedule(TimerTask任務，日期firstTime，長周期)安排指定任務從指定時間開始重複執行fixed-delay
  用法：

public void schedule(TimerTask task, Date firstTime, long period)
參數：
task - task to be scheduled.
firstTime - First time at which task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if firstTime.getTime() < 0,
 or period <= 0
IllegalStateException - if task was already scheduled 
or cancelled, timer was cancelled, 
or timer thread terminated.
NullPointerException - if task or firstTime is null

// Java program to demonstrate
//schedule method calls of Timer class
import java.util.Timer;
import java.util.TimerTask;
class Helper extends TimerTask
{
    public static int i = 0;
    public void run()
    {
        System.out.println("Timer ran " + ++i);
    }
}
public class Test
{
    public static void main(String[] args)
    {
         
        Timer timer = new Timer();
        TimerTask task = new Helper();
         
        timer.schedule(task, 2000, 5000);
         
    }
}

輸出：

Timer ran 1
Timer ran 2
Timer ran 3
Timer ran 4
Timer ran 5
.
.
.

• Schedule(TimerTask任務，長延遲)：java.util.Timer.schedule(TimerTask任務，長延遲)安排指定的任務在指定的延遲後執行
  用法：

public void schedule(TimerTask task, long delay)
參數：
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
Throws:
IllegalArgumentException - if delay is negative,
or delay + System.currentTimeMillis() is negative.
IllegalStateException - if a task was already scheduled 
or cancelled, the timer was cancelled, 
or timer thread terminated.
NullPointerException - if task is null

• Schedule(TimerTask任務，長延遲，長周期)：java.util.Timer.schedule(TimerTask任務，長延遲，長周期)安排指定的任務重複執行fixed-delay，在指定的延遲後開始用法：
  

public void schedule(TimerTask task, long delay, long period)
參數：
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay < 0, 
or delay + System.currentTimeMillis() < 0, or 
period <= 0
IllegalStateException - if task was already scheduled 
or cancelled, timer was cancelled, 
or timer thread terminated.
NullPointerException - if task is null

• ScheduleAtFixedRate(TimerTask任務，日期firstTime，長周期)：java.util.Timer.scheduleAtFixedRate(TimerTask任務，日期firstTime，長周期)安排指定任務從指定時間開始重複執行fixed-rate用法：
  

public void scheduleAtFixedRate(TimerTask task, Date firstTime, long period)
參數：
task - task to be scheduled.
firstTime - First time at which task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if firstTime.getTime() <
0 or period <= 0
IllegalStateException - if task was already scheduled
 or cancelled, timer was cancelled, 
or timer thread terminated.
NullPointerException - if task or firstTime is null

• ScheduleAtFixedRate(TimerTask任務，長延遲，長周期)：java.util.Timer.scheduleAtFixedRate(TimerTask任務，長延遲，長周期)安排指定的任務重複執行fixed-rate，在指定的延遲後開始用法：
  

public void scheduleAtFixedRate(TimerTask task, long delay, long period)
參數：
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay < 0, 
or delay + System.currentTimeMillis() < 0, or 
period <= 0
IllegalStateException - if task was already 
scheduled or cancelled, timer was cancelled, 
or timer thread terminated.
NullPointerException - if task is null

// Java program to demonstrate
// scheduleAtFixedRate method of Timer class
import java.util.Timer;
import java.util.TimerTask;
import java.util.*;
class Helper extends TimerTask
{
    public static int i = 0;
    public void run()
    {
        System.out.println("Timer ran " + ++i);
        if(i == 4)
        {
            synchronized(Test.obj)
            {
                Test.obj.notify();
            }
        }
    }
     
}
public class Test
{
    protected static Test obj;
    public static void main(String[] args) throws InterruptedException
    {
        obj = new Test();
         
        //creating a new instance of timer class
        Timer timer = new Timer();
        TimerTask task = new Helper();
        //instance of date object for fixed-rate execution
        Date date = new Date();
        timer.scheduleAtFixedRate(task, date, 5000);
         
        System.out.println("Timer running");
        synchronized(obj)
        {
            //make the main thread wait
            obj.wait();
             
            //once timer has scheduled the task 4 times, 
            //main thread resumes
            //and terminates the timer
            timer.cancel();
             
            //purge is used to remove all cancelled 
            //tasks from the timer'stack queue
            System.out.println(timer.purge());
        }
    }
}

輸出：

Timer running
Timer ran 1
Timer ran 2
Timer ran 3
Timer ran 4
0

參考：

• Oracle