同じ優先度の要素のFIFO順序を維持する優先度ブロックキューをJavaで作成しようとしています。Oracleのドキュメントはそれについていくらかの助けを提供します、しかし私はまだ非常に絡み合っています。
次のトピックはすべて私にとって非常に新しいものであることに注意してください：Generics、Interfaces as Types、およびstaticnestedclasses。これらはすべて、次のクラス定義で機能します。特にジェネリックは紛らわしいので、ここで完全に台無しにしたと思います。
現在発生しているコンパイラエラーを特定するためのコメントを含めました。
いくつかの具体的な質問：
クラスがキューに入れられたイベントオブジェクトを表し、実際のキューが静的クラスメンバーであっても大丈夫ですか？
OracleのFIFOイベント「ラッパー」を静的なネストされたクラスとして含めることは合理的でしたか？
私は少なくともここで正しい方向に進んでおり、すべてを1つの外部クラスで行っていますか？
これが私が書いたクラスです：
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,
}
}