<!DOCTYPE qhelp PUBLIC

"-//Semmle//qhelp//EN"

"qhelp.dtd">

<qhelp>

<overview>

<p>

Fields that are never read at runtime are unnecessary and should be removed.

</p>

<include src="DeadCodeSummary.inc.qhelp"/>

<p>

Fields are considered dead if at runtime they are never read directly or indirectly, for example

through a framework or a use of reflection. Any field which is not dead is considered to be "live".

</p>

<p>

Fields are considered to be dead if they are only written to, and never read.

</p>

<include src="DeadCodeDetails.inc.qhelp"/>

</overview>

<recommendation>

<p>

Before making any changes, confirm that the field is not required by verifying that the field is

only read from dead methods. This confirmation is necessary because there may be project-specific

frameworks or techniques which can introduce hidden dependencies. If this project is for a library,

then consider whether the field is part of the external API, and may be used in external projects

that are not included in the snapshot.

</p>

<p>

After confirming that the field is not required, remove the field. You will also need to remove any

references to this field, which may, in turn, require removing other unused classes, methods

and fields.

</p>

<include src="DeadCodeExtraEntryPoints.inc.qhelp"/>

</recommendation>

<section title="Example 1">

<p>

In the following example, we have a class containing a single field called <code>deadField</code>:

</p>

<sample src="DeadField.java" />

<p>

The field is only read from the method <code>getDeadField</code>. However, <code>getDeadField</code>

is never called, so the field is never read at runtime. The field is therefore marked as dead.

</p>

</section>

<section title="Example 2">

<p>

In this example, we have another class containing a single field called <code>writtenToField</code>:

</p>

<sample src="DeadFieldWrittenTo.java" />

<p>

The field is written to in the method <code>runThing</code>, which is live because it is called by

the <code>main</code> method. However, the field is never read at runtime, only written to. The

field is therefore marked as dead.

</p>

</section>

<section title="Example 3">

<p>

In this example, we have a class representing something that can be serialized to and from XML:

</p>

<sample src="DeadFieldSerialized.java" />

<p>

The field <code>field</code> is written and read by the serialization framework in order to store

the contents of the object in an XML file, or to construct an instance of the object from an XML

file. The field is therefore considered to be read at runtime, which makes the field live.

</p>

</section>

<include src="DeadCodeReferences.inc.qhelp" />

</qhelp>