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plurals

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primarykey
Id
9423123
data
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0
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8
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2012-02-23T23:29:19.113
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2012-02-24T14:35:31.587
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2017-05-23T11:56:41.670
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697449
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2
Score
8
ViewCount
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text
Body
Mixing generics and raw types isn't going to work. If you need these interfaces to reference each other, they also need to reference themselves: <pre><code>interface Player<R, P extends Player<R, P, G>, G extends Game<R, G, P>> { R takeTurn(G game); } interface Game<R, G extends Game<R, G, P>, P extends Player<R, P, G>> { void play(P player); } </code></pre> Although this is looking rather hairbrained, and I'm not sure why you need it. Edit: I was able to implement your <code>AbstractGame</code> based on the above: <pre><code>abstract class AbstractGame<R, P extends Player<R, P, AbstractGame<R, P>>> implements Game<R, AbstractGame<R, P>, P> { public final void play(final P player) { final R value; value = player.takeTurn(this); turnTaken(value); } protected abstract void turnTaken(R value); } </code></pre> However I couldn't quite close the circuit with <code>XGame</code> and <code>XPlayer</code>: <pre><code>public class XGame extends AbstractGame<Integer, XPlayer> //compile error on XPlayer { protected void turnTaken(Integer value) { } } public class XPlayer implements Player<Integer, XPlayer, XGame> //compile error on XGame { @Override public Integer takeTurn(final XGame game) { return (42); } } </code></pre> The issue seems to be that each of the generic declarations of <code>XGame</code> and <code>XPlayer</code> needs the other to be correct. This is where your design is truly cyclical. If the compiler 'assumed' each was correct, it would in theory work. But it doesn't. Edit 2: How about this: <pre><code>interface Game<R, G extends Game<R, G>> { void play(Player<R, G> player); } interface Player<R, G extends Game<R, G>> { R takeTurn(G game); } abstract class AbstractGame<R, G extends AbstractGame<R, G>> implements Game<R, G> { public final void play(final Player<R, G> player) { final R value; value = player.takeTurn(self()); turnTaken(value); } protected abstract G self(); protected abstract void turnTaken(R value); } public final class XGame extends AbstractGame<Integer, XGame> { protected XGame self() { return this; } protected void turnTaken(Integer value) { } } public class XPlayer implements Player<Integer, XGame> { @Override public Integer takeTurn(final XGame game) { return (42); } } </code></pre> The key here was declaring an abstract method <code>self()</code> in <code>AbstractGame</code> that returns an instance of type <code>G</code>. Extending classes must resolve the inherited type parameter with their own type, and implement <code>self()</code> to return <code>this</code>. This is only suitable for internal code, since an extending class could easily lie, for example: <pre><code>public class EvilGame extends AbstractGame<Integer, AnotherGame> { ... } </code></pre> See my answer <a href="https://stackoverflow.com/a/7355094/697449">here</a> and <a href="https://stackoverflow.com/questions/7959335/self-bound-generic-type-with-fluent-interface-and-inheritance">this post</a> for more details on this pattern.
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