package practises.thread;

public abstract class timertask implements Runnable
{
    boolean cancelled = false;   //取消狀態 
    long nextTime = -1;          //下一定時 
    long period;                 //執行間隔 
    boolean fixedRate;           //勻速執行標志
    
    protected timertask() {} 
    
    //取消任務執行，如果在運行，返回true，或者如果已被取消或從未定時，返回false
    public boolean cancel() 
    {
      if (cancelled) 
        return false;         
      cancelled = true;                    
      if (nextTime == -1) 
        return false;    
      return true;
    }  
    
    //定時器指定和時執行，run()方法用來確定是否在贏得時候被調用
    public long scheduledExecutionTime() 
    { 
      return nextTime; 
    } 
    
    //子類必須覆蓋這一方法，提供要運行的代碼
    //timer類從內部線程調用它
    public abstract void run();
    
    //由timer來告訴task的定時情況
    void schedule(long nextTime, long period, boolean fixedRate) 
    {
	this.nextTime = nextTime;
	this.period = period;
	this.fixedRate = fixedRate;
    } 
    
    //在timer調用后將timer取消
    boolean reschedule() 
    {
	if (period == 0 || cancelled) return false; 
	if (fixedRate) 
	  nextTime += period;
	else 
	  nextTime = System.currentTimeMillis() + period;
	return true;
    }       	
}