Java: Sort an array using external parameters

Question

Say I have a function foo, with some parameters. In this function I generate an array m of type Move. I now need to sort this array. Ok, so I break out Arrays.sort(m, Comparator() { ... }. But wait, the function I want to use to compare two moves needs to take the parameters of foo into account, yet a Comparator's compare function can only take two arguments of type Move! See following code for what I want to do.

public int compare (Move m1, Move m2, Game g, int id) {
    return g.evaluate(m1, g, id) - g.evaluate(m2, g, id);
}


public int foo (Game g, int id) {
    Move[] m = ... ;

    ???

    // m is now sorted by compare(move1, move2, g, id)
}

I do not have access to the Game class itself, so I can't just edit that to solve my problem. The Comparator class seems unable to do this. Is there any way to actually do this in Java?

You can create a wrapper around game and then sort that using a comparator . — StackFlowed
– StackFlowed, Commented Oct 29, 2014 at 20:04
Make a MoveComparator class that is constructing using a Game and an int, and stores them as instance variables. The MoveComparator can then compare the two Moves it's passed using the Game and int it already has. — that other guy
– that other guy, Commented Oct 29, 2014 at 20:04
You could subclass comparator and provide your parameters to it rather that use an anonymous comparator. Then in your implementation which is doing the comparisons you could use those values. — mkobit
– mkobit, Commented Oct 29, 2014 at 20:05
You can also write your Comparator as an anonymous class, and use g and id directly if you make them final. — azurefrog
– azurefrog, Commented Oct 29, 2014 at 20:07

ToYonos · Accepted Answer · 2014-10-29 20:10:00Z

5

Build your own Comparator :

public MyComparator implements Comparator<Move>
{

    private Game game;
    private int id;

    public MyComparator(Game g, int id)
    {
         this.game = g;
         this.id = id;
    }

    // compare function, using game and I'd
 }

Use it like that :

 Move[] m = ... ;
Arrays.sort(m, new MyComparator(aGame, and));

answered Oct 29, 2014 at 20:10

ToYonos

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