Comparator return type is not compatible with integer

Question

I am trying to sort an object via the object attribute NodeID which is long type.

 Collections.sort(PeerNodeInChord, new Comparator<PeerNode>() 
       {
           @Override public long compare(PeerNode p1, PeerNode p2) 
           {
                 return p1.NodeID - p2.NodeID; // Ascending
           }

       });

I am getting the following error :

compare(PeerNode,PeerNode) in cannot implement compare(T,T) in Comparator return type long is not compatible with int where T is a type-variable: T extends Object declared in interface Comparator

It seems i cant have type "long" as return type and must have "int" as the return type.

I am not allowed to change NodeID type to int.

Is there any way to sort the ArrayList of PeerNode via the object attribute NodeID which is long type ??

Answer 1

Don't reinvent the wheel and simply delegate to the compare method from Long:

@Override 
public int compare(PeerNode p1, PeerNode p2) {
    return Long.compare(p1.NodeID, p2.NodeID);
}

Out of curiosity, you can give a look to the Long.compare implementation which is:

public static int compare(long x, long y) {         
    return (x < y) ? -1 : ((x == y) ? 0 : 1);     
}

Answer 2

Collections.sort(PeerNodeInChord, new Comparator<PeerNode>() {
    @Override 
    public int compare(PeerNode p1, PeerNode p2) {
        long dif = p1.NodeID - p2.NodeID;
        if (dif > 0) return 1;
        if (dif < 0) return -1;
        return 0; 
    }
});