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POIs IllegalStateException appropriate for an immutable object?
 

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  1. POIs IllegalStateException appropriate for an immutable object?
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    <p>Would you throw an <code>IllegalStateException</code> if:</p> <ol> <li>A method is unable to do its job because of the value(s) of one or more fields</li> <li>Those fields are <code>final</code> and assigned only in the constructor?</li> </ol> <p>Textbook example: your class is an immutable <code>Collection&lt;BigInteger&gt;</code> and your method is supposed to return the maximum element, but this instance is empty.</p> <p>I have read <a href="http://smallwig.blogspot.com/2008/06/common-java-unchecked-exception-types.html" rel="nofollow noreferrer">Kevin Bourillon`s blog post</a> on the subject and I am not sure which rule applies.</p> <blockquote> <p>UnsupportedOperationException - this means that the method invoked will always fail for an instance of this class (concrete type), regardless of how the instance was constructed.</p> </blockquote> <p>Definitely not. Many instances of this class are not empty and the operation would have succeeded.</p> <blockquote> <p>IllegalStateException - ... there does exist at least one alternate state that the instance in question could have been in, which would have passed the check ... &lt;snip&gt; ... Note also that this exception is appropriate whether or not it is possible to actually mutate this aspect of the instance's state, or it's already too late.</p> </blockquote> <p>Not quite. This instance was constructed with zero length, so <em>this instance</em> is not and could never have been non-empty.</p> <blockquote> <p>IllegalArgumentException - throwing this exception implies that there exists at least one other value for this parameter that would have caused the check in question to pass.</p> </blockquote> <p>Might apply if the parameter in question is the implicit <code>this</code> parameter. This is the exception I am tempted to throw, but I am concerned that it could be confusing.</p> <hr> <p><strong>Update</strong>: changed example from <code>Collection&lt;Integer&gt;</code> to <code>Collection&lt;BigInteger&gt;</code> because the fact that there was an identity element (<code>Integer.MIN_VALUE</code>) distracts from the question.</p>
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    1. COThere are two different things in this question. **One** is to have an utility method, that returns the maximum of a given collection ( which as Jon points, is just like Collections.max method ) The **other** is in your question title, an *immutable object* having a max method, returning either, the max value of a delegated object, or the from himself. This second scenario is the one I'm answering http://stackoverflow.com/questions/3267958/is-illegalstateexception-appropriate-for-an-immutable-object/3268353#3268353
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