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我試圖在Java中創建一個優先級阻止隊列，該優先級阻止隊列爲具有相同優先級的元素保持FIFO順序。 Oracle文檔提供了一些幫助，但我仍然很糾結。如何創建保留FIFO行爲的Java PriorityBlockingQueue？
我應該注意的是，以下主題都非常新的對我說：泛型，接口，類型，並靜態嵌套類。所有這些都在下面的類定義中起作用。泛型，尤其是混淆，我相信我在這裏完全搞砸了他們。
我已經包含了評論來識別我目前正在收到的編譯器錯誤。
幾個具體的問題：
是不是好有類代表排隊的事件對象，與實際隊列爲類的靜態成員？
將Oracle的FIFO事件「包裝器」包含爲靜態嵌套類是否合理？
我是否至少在正確的軌道上，在一個外部課堂上做這一切？
這裏是我寫的類：通過您的代碼
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.atomic.AtomicLong;
public class FIFOPBQEvent {
/**
* First we define a static nested class which, when instantiated,
* encapsulates the "guts" of the event - a FIFOPBQEvent - along with
* a sequence number that assures FIFO behavior of events of like priority.
*
* The following is lifted ALMOST verbatim (I added "static" and some
* comments) from Oracle documentation on adding FIFO-ness to a Priority
* Blocking Queue:
* http://download.oracle.com/javase/6/docs/api/java/util/concurrent/PriorityBlockingQueue.html
* As the Oracle doc points out:
*
* "A static nested class interacts with the instance members of its outer
* class (and other classes) just like any other top-level class. In
* effect, a static nested class is behaviorally a top-level class that
* has been nested in another top-level class for packaging convenience."
*
*/
static class FIFOEntry<E extends Comparable<? super E>> implements
Comparable<FIFOEntry<E>> {
final static AtomicLong seq = new AtomicLong();
final long seqNum; // instance
final E entry;
public FIFOEntry(E entry) {
seqNum = seq.getAndIncrement();
this.entry = entry;
}
public E getEntry() {
return entry;
}
/** Here is implementation of Comparable */
public int compareTo(FIFOEntry<E> other) {
int res = entry.compareTo(other.entry);
if (res == 0 && other.entry != this.entry)
res = (seqNum < other.seqNum ? -1 : 1);
return res;
}
}
/**
* Now we declare a single (static) PBQ of FIFO entries into which
* PBQFIFOEvents will be added and removed.
*/
/** FLAGGED AS ERROR BY COMPILER */
// Bound mismatch: The type FIFOPBQEvent is not a valid substitute for the
// bounded parameter <E extends Comparable<? super E>> of the type
// FIFOPBQEvent.FIFOEntry<E>
private static PriorityBlockingQueue<FIFOEntry<FIFOPBQEvent>> theQueue =
PriorityBlockingQueue<FIFOEntry<FIFOPBQEvent>>();
/**
* And here are the "guts" of our event: the i.d. and state of the GUI widget
*/
private ConsoleObject obj = ConsoleObject.UNDEFINED_OBJ; // widget that was affected
private ObjectState state = ObjectState.UNDEFINED_STATE; // the widget's new state
/**
* Constructor specifying the class variables
*/
public FIFOPBQEvent(ConsoleObject theObj, ObjectState theState) {
obj = theObj;
state = theState;
}
/**
* Event queuing ("sending") and dequeuing ("receiving")
*/
public void sendEvent() {
/** FLAGGED AS ERROR BY COMPILER */
// The method put(FIFOPBQEvent.FIFOEntry<FIFOPBQEvent>) in the type
// PriorityBlockingQueue<FIFOPBQEvent.FIFOEntry<FIFOPBQEvent>> is not
// applicable for the arguments (FIFOPBQEvent)
theQueue.put(this);
}
public static FIFOPBQEvent receiveEvent() {
/** FLAGGED AS ERROR BY COMPILER */
// Type mismatch: cannot convert from FIFOPBQEvent.FIFOEntry<FIFOPBQEvent>
// to FIFOPBQEvent
FIFOPBQEvent event = theQueue.take();
return event;
}
/**
* ConsoleEvent accessors
*/
public ConsoleObject getObj() {
return this.obj;
}
public ObjectState getState() {
return this.state;
}
/**
* And for the first time, enums instead of public static final ints.
*/
public enum ConsoleObject {
UNDEFINED_OBJ,
RESERVED,
/** Console keys */
RESET,
DISPLAY_MAR,
SAVE,
INSERT,
RELEASE,
START,
SIE,
SCE,
/** Console toggle switches */
POWER,
PARITY_CHECK,
IO_CHECK,
OVERFLOW_CHECK,
SENSE_SWITCH_1,
SENSE_SWITCH_2,
SENSE_SWITCH_3,
SENSE_SWITCH_4
}
public enum ObjectState {
UNDEFINED_STATE,
/** Toggle switches */
OFF,
ON,
/** Console keys */
PRESSED,
}
}
'FIFOPBQEvent'沒有實現'可比'這會導致一些你的錯誤那裏。您的FIFOEntry的通用聲明需要實現Comparable接口的對象。 –
Bringer128