可比和比较

Question

I have a problem. I have a class that extends another class and implements Comparable. But when I tried to compile my program I had this error: Flight is not abstract and does not override abstract method compareTo. Anyway, the code of Flight is this:

class Flight extends KeyFlight implements Comparable<Flight>{

 public KeyFlight kf;
 public boolean departure;

 public void Flight(){
 KeyFlight kf=new KeyFlight();
 boolean departure=false;
 }

 public int compareTo(KeyFlight other){
  if (kf.time==other.time){
  if (kf.key<other.key){
   return kf.key;
  } else {
   return other.key;
  } 
 } else {
  if (kf.time <other.time){
   return kf.key;
  } else {
   return other.key;
  }  
 }
}
}

Thank you in advance!

Answer 1

You should use

implements Comparable<KeyFlight>

Instead of

implements Comparable<Flight>

As you want to compare two keyflights rather than flights itself. The Type of parameter that you defines in compareTo, should match with the type you specified in implements clause that you are going to compare with.

Another issue with your code is, in your constructor you are re-defining KeyFlight, it should be

public void Flight(){
    kf=new KeyFlight();

Else you will get NullPointerException in future. Same applies for your departure boolean.

A side note, By Default in java boolean is initialised to false, so you don't have to explicitly say that in constructor.

Answer 2

我认为compareTo的参数类型是错误的，应该是

public int compareTo(Flight other){

Answer 3

The compareTo method in your class is not to a valid override because you define that your class implement Comparable<Flight> So in order to override this method in your class you need to change the variable type of other from KeyFlight to Flight .

 @Override
 public int compareTo(Flight o) {
  //your logic here
 }