我对Priority Queue如何工作的理解不正确，或者我的compareTo方法中的逻辑错误覆盖了Comparable接口。我正在尝试将优先级最高的跑道分配给着陆或起飞的飞机。在以下场景中，有四个航班和四个跑道可用。因此，每架航班都会在预定的时间降落或离开。
格式为：
scheduledTime|eventType|flightIdentifier|runwayUsed
00:01|ARRIVAL|A001|null
00:00|DEPARTURE|D001|null
00:01|DEPARTURE|D002|null
00:00|DEPARTURE|D003|null
在分配到优先跑道的航班（从跑道对象的优先级队列'轮询'优先跑道）后，结果是
00:01|ARRIVAL|A001| 1
00:00|DEPARTURE|D001| 4
00:01|DEPARTURE|D002| 2
00:00|DEPARTURE|D003| 3
但是，假设我的compareTo方法中没有逻辑错误，则输出应为：
00:01|ARRIVAL|A001| 1
00:00|DEPARTURE|D001| 2
00:01|DEPARTURE|D002| 3
00:00|DEPARTURE|D003| 4
这是包含compareTo方法的Runway类：
public class Runway implements Comparable<Runway>{
//instance or class variables
private LocalTime whenAvailable; //when the runway is available
private LocalTime actualTime; //actual time the plane arrived or departed
private List<Flight> flights; //the flights that have been assigned to the runway
private Integer runwayNumber; // the number of the runway. for ex., 1 = Runway 1.
private LocalTime previousSchedTime; //the most recent previous time that the runway was scheduled for arrival or departure. This is just used
// for testing purposes.
/**
* Constructor
*/
protected Runway() {
whenAvailable = null;
flights = new ArrayList<Flight>();
}
/**
* Determine if the runway is available
* @param currentTime The scheduled time of the flight
* @return true if the runway is available or false if it is not
*/
protected boolean isAvailable(LocalTime currentTime) {
if(currentTime == null) {
throw new IllegalArgumentException();
}
return whenAvailable == null || !currentTime.isBefore(whenAvailable); // currentTime >= whenAvailable
}
/**
* Assign flight to the runway, i.e., set the actual time a flight uses the runway and the time ruwnay will be available again
* @param flight The flight being assigned to the runway
* @param scheduledTime The scheduled time of the flight
* @param reserveTime The arrival or departure reserve times of the flight
*/
protected void assignFlight(Flight flight, LocalTime scheduledTime, int reserveTime) {
//if the runway is available
if(isAvailable(scheduledTime)) {
//Set the actual time of the flight and when the runway will be available again
//if the runway is null and available
if(whenAvailable == null) {
actualTime = scheduledTime;
whenAvailable = scheduledTime.plusMinutes(reserveTime);
}
//if runway is available and the scheduled time of flight is equal to when the runway is available
else if(scheduledTime == whenAvailable || scheduledTime.isBefore(whenAvailable)) {
actualTime = whenAvailable;
whenAvailable = actualTime.plusMinutes(reserveTime);
}
else { //if scheduledTime > whenAvailable
actualTime = scheduledTime;
whenAvailable = actualTime.plusMinutes(reserveTime);
}
}
//if the runway is not available aka currentTime < whenAvailable
else {
actualTime = whenAvailable;
whenAvailable = actualTime.plusMinutes(reserveTime);
}
flights.add(flight);
previousSchedTime = scheduledTime; //update previousSchedTime to scheduledTime
}
/**
*
* @return acutialTime the runway was used by flight
*/
protected LocalTime getActualTimeRunway() {
return actualTime;
}
/**
*
* @return the time the runway is available
*/
protected LocalTime getWhenAvailable() {
return whenAvailable;
}
/**
*
* @return List of all the flights that used the runway
*/
protected List<Flight> getFlights(){
List<Flight> tmpList = new LinkedList<Flight>();
for(Flight f : flights) {
tmpList.add(f);
}
return tmpList;
}
/**
*
* @param runwayNumber set the number of the runway
*/
protected void setRunwayNumber(int runwayNumber) {
if(runwayNumber < 1) {
throw new IllegalArgumentException();
} //end of if
this.runwayNumber = runwayNumber;
}
/**
*
* @return the number of the runway
*/
protected Integer getRunwayNumber() {
return runwayNumber;
}
/**
*
* @return the most recent previous time that the runway was scheduled for arrival or departure. This is used
// as a condition in the assignFlight method below
*/
protected LocalTime getPreviousSchedTime() {
return previousSchedTime;
}
/**
* NOTE: this is intended to only be used for testing in other classes when used with reflection
* @param previousSchedTime sets the previousScedTime
*/
private void setPreviousSchedTime(LocalTime previousSchedTime) {
this.previousSchedTime = previousSchedTime;
}
/**
* Override compareTo method of Comparable interface
* Set priority of runway instance when compared other runway instances
*/
@Override
public int compareTo(Runway other) {
if(this.getWhenAvailable() == null && other.getWhenAvailable() == null) {
return 0;
}
else if(this.getWhenAvailable() == null && other.getWhenAvailable() != null) {
return -1;
}
else if(this.getWhenAvailable() !=null && other.getWhenAvailable() == null) {
return 1;
}
else if(this.getWhenAvailable() !=null && other.getWhenAvailable() != null) {
if(this.getWhenAvailable().equals(other.getWhenAvailable())) {
return 0;
}
else if(this.getWhenAvailable().isBefore(other.getWhenAvailable())) {
return -1;
}
else if(this.getWhenAvailable().isAfter(other.getWhenAvailable())) {
return 1;
}
}
return 0;
}
/**
* Intended use is only for JUnit testing when used with reflection
* @param wA set whenAvailable time
*/
private void setWhenAvailable(LocalTime wA) {
this.whenAvailable = wA;
}
} // Runway类的结尾----------------------------------------
下面是一个通过优先级队列实现compareTo方法的类：
public class stackExchange {
public static void main(String[] args) {
Flight f1 = new Flight("00:01", "ARRIVAL","A001");
Flight f2 = new Flight("00:00", "DEPARTURE","D001");
Flight f3 = new Flight("00:01", "DEPARTURE","D002");
Flight f4 = new Flight("00:00", "DEPARTURE","D003");
PriorityQueue<Flight> flightsPQ = new PriorityQueue<Flight>();
flightsPQ.add(f1);
flightsPQ.add(f2);
flightsPQ.add(f3);
flightsPQ.add(f4);
Runway r1 = new Runway();
r1.setRunwayNumber(1);
Runway r2 = new Runway();
r2.setRunwayNumber(2);
Runway r3 = new Runway();
r3.setRunwayNumber(3);
Runway r4 = new Runway();
r4.setRunwayNumber(4);
PriorityQueue<Runway> runwaysPQ = new PriorityQueue<Runway>();
runwaysPQ.add(r1);
runwaysPQ.add(r2);
runwaysPQ.add(r3);
runwaysPQ.add(r4);
while(!flightsPQ.isEmpty()) {
Flight tmpFlight = flightsPQ.poll(); //remove priority flight from flightsPQ
Runway tmpRunway = runwaysPQ.poll(); //remove priority runway from runwaysPQ
tmpRunway.assignFlight(tmpFlight, tmpFlight.getScheduledTime(), tmpFlight.getReserveTime()); //assign the priority flight to the runwy
tmpFlight.setActualTime(tmpRunway.getActualTimeRunway()); //set the actual time the flight was used
tmpFlight.setRunwayUsed(tmpRunway); //tell the flight which runway it used
//print out the flight data that used the runway and the number of the runway used
//format: scheduledTime of flight | eventType | identifier | actualTime the flight used the runway | the number of the runway used (used to distinguish runway over
// other runways
System.out.println(tmpFlight.getScheduledTime() + "|" + tmpFlight.getEvent() + "|" + tmpFlight.getIdent() + "|" + tmpFlight.getActualTime()
+ "|" + tmpFlight.getRunwayUsed().getRunwayNumber());
runwaysPQ.add(tmpRunway); //add the runway back into runwaysPQ
}
} //end of main
} // stackExchange类的结尾
答案 0 :(得分：1)
在开头create-react-app <project>为空，因此所有跑道都具有相同的优先级。根据文件：
此队列的头部是指定排序的最小元素。如果多个元素绑定的值最小，那么头部就是其中一个元素 - 关系被任意打破。
所以你应该首先比较可用时间，如果你想要一致的订购，还要比较跑道的数量。