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    <p>The A- and B-items should probably implement the same interface, such as</p> <pre><code>boolean canMove(State newState); // A-items know which B-items to check void performMove(State newState, HistoryAndLog historyAndLog); // A-items and B-items will record history and log as appropriate. A-item will change related B-items as appropriate </code></pre> <p>In this case we are using composite (A-items check if related B-items can change state as desired) and delegation (have A- and B-items update the log and store history as they see fit). This removes the need for a lot of the if-statements.</p> <p>The underlying design of the A- and B-items should probably be "state pattern", perhaps combined with Flyweight so you can use an underlying transition matrix to implement part of the logic. </p> <p>EDIT: Expanding on Flyweight... For an N x M transition matrix, storing just a yes/no value takes one bit. If instead you have to store an object pr. cell, that would cost a LOT more (internal representaiton of object). Instead it's cheaper to create a temporary object on request from a factory class. Often by a factor of 100 or more pr. object.</p> <p>Basically you are trading computation in the situation (create the object on demand) for storage (avoid storing N x M objects).</p> <p>One could imagine something like this</p> <pre><code>class Factory { private boolean canTransitionItemA(final int n, final int m) { // Look up in matrix } public ItemType makeItemAFromCoordinates(final int n, final int m) { return new ItemA() { public boolean canTransition(&lt;blabla&gt;) { return canTransitionItemA(n, m) &amp;&amp; canTransitionRelatedBItems(n, m); } &lt;bla bla bla&gt; } } } </code></pre>
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    1. COPlease, more details. I'm unfamiliar with Flywight pattern. And I can't figure out whai is needed for?
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    2. CODone, but I think that Flyweight distracts a little from the issue you really care about. It's just a more efficient way to represent your state transition table as objects when needed by lazy-creating objects on request.
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    3. COCan I use singleton-state-items instead of Flyiweigh pattern? Means each my state (there will be about 20) will be a singleton bean.
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