inference variable T has incompatible bounds Error

Question

ArrayList<ShipDetail> detailArray = new ArrayList<ShipDetail>(Arrays.asList(shipDetail));
Sorter.QuickSort( detailArray );

And this is my Sorter class in which I was trying to do Implement some algorithms.

public class Sorter
{
   public static<T extends Comparable<T>> void QuickSort(AbstractList<T> collection )
   {
        quickSort(collection,0,collection.size()-1);
   }

}

But while compiling i am getting the following error :

required: AbstractList found: ArrayList reason: inference variable T has incompatible bounds equality constraints: ShipDetail upper bounds: Comparable where T is a type-variable: T extends Comparable declared in method QuickSort(AbstractList)

Is `ShipDetail` comparable to itself? This is required (note `>`) — mszymborski, Jan 31 '17 at 01:56
Please post the signature of that class (what it implements and extends) — mszymborski, Jan 31 '17 at 02:01
this is signature of my ship class : public class ShipDetail implements Comparator — Anmol, Jan 31 '17 at 02:02
To be more precise Comparators are objects-algorithms which provide service of comparison of other objects, while Comparables are objects which themselves allow comparing them to other kind of objects. — mszymborski, Jan 31 '17 at 02:05

mszymborski · Answer 1 · 2017-01-31T02:06:35.973

6

ShipDetail is not comparable to itself. The bound here:

<T extends Comparable<T>>

Also applies to the type variable T in the argument, which is inferred as ShipDetail.

ShipDetail should be defined as follows:

class ShipDetail implements Comparable<ShipDetail> { ...

And not:

class ShipDetail implements Comparator<ShipDetail> { ...

Comparators are objects-algorithms which provide service of comparison of other objects, while Comparables are objects which themselves allow comparing them to other kind of objects.

edited Jan 31 '17 at 02:06

answered Jan 31 '17 at 02:00

mszymborski

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Thanks now I understood difference of using Comparator and Comparable. – Anmol Jan 31 '17 at 02:09
@Anny cool!you can mark the answer with the green tick if you think it answers your question fully. – mszymborski Jan 31 '17 at 02:14

inference variable T has incompatible bounds Error

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