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<h2 class="first-section-title"><a name="330"></a><a name="ch10lev1sec3"></a>Common Mistakes</h2><p class="first-para">
<b class="bold">Populating VOs inconsistently.</b> I've seen some applications where fields of value objects were populated with different value sets depending on usage context. This practice is error prone and leads to bugs. It's also confusing for developers to maintain, especially if they weren't involved in the initial development effort. Usually, this practice is a red flag indicating that the design is process oriented instead of object oriented.</p>
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<b class="bold">Using a blank string to avoid a </b><b class="bold"><span class="fixed">NullPointerException</span></b>. Some developers initialize all fields to a blank string or something that means "null" but really isn't, as in the following:</p>
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private String _customerName = "";
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<p class="para">Although this kind of declaration eliminates <span class="fixed">NullPointerException <a name="331"></a><a name="IDX-134"></a>exceptions</span>, it doesn't prevent some other type of derivative exception from appearing down the line. This practice is akin to "sweeping dirt under the rug" and is best avoided.</p>
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<b class="bold">Maintaining parent-child relationships for VOs in both directions.</b> For example, the <span class="fixed">CustomerVO</span> would contain a collection of <span class="fixed">AccountVO</span> children, and each of the <span class="fixed">AccountVO</span> instances would contain a reference back to the parent. You run into the same problems with this practice as you do when you replicate data in relational databases. The result is double the maintenance when data is changed. Further, the practice is error prone and tends to be the root cause of bugs.</p>
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