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    copied!<p>When designing software, I find it helpful to think about how I would use a method, then write down the method signature (and if you do test driven development, the unit test), and only then think about how I would implement it.</p> <p>Doing this here, I find that the requirement</p> <blockquote> <p>Then when a player clicks a piece, the squares that are available as destination after the move will be outlined in some colour.</p> </blockquote> <p>is impossible to satisfy with a method like</p> <pre><code>void move(Square destination); </code></pre> <p>because there is no way to find out the possible moves without actually making them. To highlight the squares, it would probably be best if we had a method like</p> <pre><code>Collection&lt;Square&gt; getPossibleMoves(); </code></pre> <p>and then we could implement</p> <pre><code>void move(Square destination) { if (!getPossibleMoves().contains(destination) { throw new IllegalMoveException(); } this.location.occupyingPiece = null; this.location = destination; this.location.occupyingPiece = this; } </code></pre> <p>as for implementing getPossibleMoves:</p> <pre><code>class Pawn extends Piece { @Override Collection&lt;Square&gt; getPossibleMoves() { List&lt;Square&gt; possibleMoves = new ArrayList&lt;Square&gt;(); int dy = color == Color.white ? 1 : -1; Square ahead = location.neighbour(0, dy); if (ahead.occupyingPiece == null) { possibleMoves.add(ahead); } Square aheadLeft = location.neighbour(-1, dy); if (aheadLeft != null &amp;&amp; aheadLeft.occupyingPiece != null &amp;&amp; aheadLeft.occupyingPiece.color != color) { possibleMoves.add(aheadLeft); } Square aheadRight = location.neighbour(1, dy); if (aheadRight != null &amp;&amp; aheadRight.occupyingPiece != null &amp;&amp; aheadRight.occupyingPiece.color != color) { possibleMoves.add(aheadRight); } return possibleMoves; } } </code></pre> <p><strong>Edit</strong>:</p> <pre><code>class Knight extends Piece { @Override Collection&lt;Square&gt; getPossibleMoves() { List&lt;Square&gt; possibleMoves = new ArrayList&lt;Square&gt;(); int[][] offsets = { {-2, 1}, {-1, 2}, {1, 2}, {2, 1}, {2, -1}, {1, -2}, {-1, -2}, {-2, -1} }; for (int[] o : offsets) { Square candidate = location.neighbour(o[0], o[1]); if (candidate != null &amp;&amp; (candidate.occupyingPiece == null || candidate.occupyingPiece.color != color)) { possibleMoves.add(candidate); } } return possibleMoves; } } </code></pre>
 

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