NonAssignedFields.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>


<overview>
<p>It is good practice to initialize every field in a constructor explicitly. A field that is never 
assigned any value (except possibly <code>null</code>) just returns
the default value when it is read, or throws a <code>NullPointerException</code>.</p>

</overview>
<recommendation>

<p>A field whose value is always <code>null</code> (or the
corresponding default value for primitive types, for example <code>0</code>) is not particularly
useful. Ensure that the code contains an assignment or initialization for each field. To help
satisfy this rule, it is good practice to explicitly initialize every field in the constructor, 
even if the default value is acceptable.</p>

<p>If the field is genuinely never expected to hold a non-default value, check the statements that
read the field and ensure that they are not making incorrect assumptions about the value of the 
field. Consider completely removing the field and rewriting the statements that read it, 
as appropriate.</p>

</recommendation>
<example>

<p>In the following example, the private field <code>name</code> is not initialized in the constructor
(and thus is implicitly set to <code>null</code>), but there is a getter method to access it.</p>

<sample src="NonAssignedFields.java" />

<p>Therefore, the following code throws a <code>NullPointerException</code>:</p>

<sample language="java">Person p = new Person("Arthur Dent", 30);
int l = p.getName().length();</sample>

<p>To fix the code, <code>name</code> should be initialized in the constructor by adding the 
following line: <code>this.name = name;</code></p>
</example>
</qhelp>