相关疑难解决方法(0)

什么List<?>意思,它只是意味着一个未指定类型的对象列表？

谷歌搜索字符串<?>返回没有任何用处(:

<?>从www.JavaPractices.com复制的此代码中令牌的含义是什么？当我用更常规的<T>用于泛型类型的替换它时,它无法编译.(错误:T无法解析为某种类型.)为什么？

// <?> occurs 3 times in the entire program.  When it is replaced with <T> the
// program no longer compiles.

void activateAlarmThenStop()
{
    Runnable myPeriodicTask = new PeriodicTask();
    ScheduledFuture<?> soundAlarmFuture = 
        this.executorService.scheduleWithFixedDelay(myPeriodicTask, 
                                          startT, 
                                          period, 
                                          TimeUnit.SECONDS
                                         );
    Runnable stopAlarm = new StopAlarmTask(soundAlarmFuture);
    this.executorService.schedule(stopAlarm, stopT, TimeUnit.SECONDS);
}

private final class StopAlarmTask implements Runnable 
{
    StopAlarmTask(ScheduledFuture<?> aSchedFuture)
    {
        fSchedFuture = aSchedFuture;
    }

    public void run() 
    {
        CConsole.pw.println("Stopping alarm.");
        fSchedFuture.cancel(doNotInterruptIfRunningFlag);

        executorService.shutdown();
    }
    private ScheduledFuture<?> fSchedFuture;
}

编辑:当然,当我们使用泛型类型的标记时<T>,它必须出现在类声明中.这里没有 …