我正在尝试在查询结果中获取min distance, min speed and max speed
的记录。目前,我正在获得最短的距离,但是我面临着获取最小和最大速度的问题,我在问自己是否可以在public int compareTo(BehaviourItem otherItem)
类中添加另一个BehaviourItem
方法来达到这一目标,但是我遇到了错误Duplicate method compareTo(BehaviourItem) in type BehaviourItem
。
如何从BehaviourItem
类获得最小和最大速度?
代码:
PreparedStatement prepared = con
.prepareStatement("SELECT speed, stop_distance from behaviour where mac = ? and stop_name = ?");
prepared.setString(1, macD);
prepared.setString(1, sto_nam);
ResultSet rsBehav = prepared.executeQuery();
List<BehaviourItem> behavList = new ArrayList<BehaviourItem>();
while (rsBehav.next()) {
int distance = rsBehav.getInt("stop_distance");
int speed = rsBehav.getInt("speed");
BehaviourItem behItem = new BehaviourItem(distance, speed);
behavList.add(behItem);
}
Collections.sort(behavList);
int minDistance = behavList.get(0).getDistance();
BehaviourItem类:
public class BehaviourItem implements Comparable<BehaviourItem>{
int speed;
int distance;
public BehaviourItem(int speed, int distance) {
super();
this.speed = speed;
this.distance = distance;
}
public int getSpeed() {
return speed;
}
public void setSpeed(int speed) {
this.speed = speed;
}
public int getDistance() {
return distance;
}
public void setDistance(int distance) {
this.distance = distance;
}
@Override
public int compareTo(BehaviourItem otherItem) {
// TODO Auto-generated method stub
return Integer.compare(this.distance, otherItem.distance);
}
}
最佳答案
您不应该让BehaviourItem
实现Comparable
,因为它没有自然顺序。相反,为不同的属性实现不同的 Comparator
s。
请注意,在Java 8中,您可以像这样简单地实现Comparator
Comparator<BehaviourItem> orderBySpeed=Comparator.comparingInt(BehaviourItem::getSpeed);
相当于
Comparator<BehaviourItem> orderBySpeed=new Comparator<BehaviourItem>() {
public int compare(BehaviourItem a, BehaviourItem b) {
return Integer.compare(a.getSpeed(), b.getSpeed());
}
};
要么
Comparator<BehaviourItem> orderByDistance
=Comparator.comparingInt(BehaviourItem::getDistance);
对于其他财产。
几乎所有使用订单的收集方法都有一个重载,它支持传递
Comparator
来定义订单,而不是使用自然订单:Collections.sort(behavList, orderBySpeed);
分别
Collections.sort(behavList, orderByDistance);
您甚至可以临时创建比较器:
Collections.sort(behavList, Comparator.comparingInt(BehaviourItem::getDistance));
和
Collections.sort(behavList, Comparator.comparingInt(BehaviourItem::getSpeed));
但是即使没有排序,流API仍允许您查找最小值或最大值:
Optional<BehaviourItem> minBySpeed=behavList.stream()
.max(Comparator.comparingInt(BehaviourItem::getSpeed));