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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Checks for Coding problems</title>
<link rel="stylesheet" type="text/css" href="mystyle.css"/>
</head>
<body>
<!-- The header -->
<table border="0" width="100%" summary="header layout">
<tr>
<td><h1>Checks for Coding problems</h1></td>
<td align="right"><img src="logo.png" alt="Checkstyle Logo"/></td>
</tr>
</table>
<!-- content -->
<table border="0" width="100%" cellpadding="5" summary="body layout">
<tr>
<!--Left menu-->
<td class="menu" valign="top">
<ul>
<li>
<a href="#AvoidInlineConditionals">AvoidInlineConditionals</a>
</li>
<li>
<a href="#DoubleCheckedLocking">DoubleCheckedLocking</a>
</li>
<li>
<a href="#EmptyStatement">EmptyStatement</a>
</li>
<li>
<a href="#EqualsHashCode">EqualsHashCode</a>
</li>
<li>
<a href="#HiddenField">HiddenField</a>
</li>
<li>
<a href="#IllegalInstantiation">IllegalInstantiation</a>
</li>
<li>
<a href="#InnerAssignment">InnerAssignment</a>
</li>
<li>
<a href="#MagicNumber">MagicNumber</a>
</li>
<li>
<a href="#MissingSwitchDefault">MissingSwitchDefault</a>
</li>
<li>
<a href="#SimplifyBooleanExpression">SimplifyBooleanExpression</a>
</li>
<li>
<a href="#SimplifyBooleanReturn">SimplifyBooleanReturn</a>
</li>
</ul>
</td>
<!--Content-->
<td class="content" valign="top" align="left">
<!-- --> <a name="AvoidInlineConditionals"></a> <h2>AvoidInlineConditionals</h2> <h4>Description</h4>
<p class="body">
Detects inline conditionals.
An example inline conditional is this:
</p>
<pre class="body" >
String a = getParameter("a");
String b = (a==null || a.length&lt;1) ? null : a.substring(1);
</pre>
<p class="body">
Rationale: Some developers find inline conditionals hard to read,
so their company's coding standards forbids them.
</p>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;AvoidInlineConditionals&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="DoubleCheckedLocking"></a> <h2>DoubleCheckedLocking</h2> <h4>Description</h4>
<p class="body">
The &quot;double-checked locking&quot; idiom (DCL) tries to avoid the runtime cost
of synchronization. An example that uses the DCL idiom is this:
</p>
<pre class="body">
public class MySingleton
{
private static theInstance = null;
private MySingleton() {}
public MySingleton getInstance() {
if ( theInstance == null ) { // synchronize only if necessary
synchronized( MySingleton.class ) {
if ( theInstance == null ) {
theInstance = new MySingleton();
}
}
}
}
}
</pre>
<p class="body">
The problem with the DCL idiom in Java is that it just does not work correctly.
Using it introduces bugs that are extremely hard to track down and reproduce.
The <a href="http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html">
&quot;Double-Checked Locking is Broken&quot; Declaration</a> has an in depth explanation
of the exact problem which has to do with the semantics of the Java memory model.
</p>
<p class="body">
The DoubleCheckedLocking check will find source code where a test is wrapped in a
synchronized block that is wrapped in the same test, like in the example above.
</p>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;DoubleCheckedLocking&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="EmptyStatement"></a> <h2>EmptyStatement</h2> <h4>Description</h4>
<p class="body">
Detects empty statements (standalone ;).
</p>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;EmptyStatement&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="EqualsHashCode"></a> <h2>EqualsHashCode</h2>
<h4>Description</h4>
<p class="body">
Checks that classes that override <span class="code">equals()</span> also
override <span class="code">hashCode()</span>.
</p>
<p class="body">
Rationale: The contract of <span class="code">equals()</span> and <span class="code">
hashCode()</span> requires that equal objects have the same hashCode. Hence,
whenever you override <span class="code">equals()</span> you must override <span class="code">
hashCode()</span> to ensure that your class can be used in collections that are
hash based.
</p>
<h4>Example</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;EqualsHashCode&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="HiddenField"></a> <h2>HiddenField</h2> <h4>Description</h4>
<p class="body">
Checks that a local variable or a parameter does not shadow a field that is
defined in the same class.
</p>
<h4>Properties</h4>
<table width="100%" border="1" cellpadding="5" class="body">
<tr class="header">
<th>name</th>
<th>description</th>
<th>type</th>
<th>default value</th>
</tr>
<tr>
<td>tokens</td>
<td>tokens to check</td>
<td>subset of tokens <a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#PARAMETER_DEF">PARAMETER_DEF</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#VARIABLE_DEF">VARIABLE_DEF</a></td>
<td><a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#PARAMETER_DEF">PARAMETER_DEF</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#VARIABLE_DEF">VARIABLE_DEF</a></td>
</tr>
</table>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;HiddenField&quot;/&gt;
</pre>
<p class="body">
To configure the check so that it checks local variables but not parameters:
</p>
<pre class="body">
&lt;module name=&quot;HiddenField&quot;&gt;
&lt;property name=&quot;tokens&quot; value=&quot;VARIABLE_DEF&quot;/&gt;
&lt;/module&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="IllegalInstantiation"></a> <h2>IllegalInstantiation</h2> <h4>Description</h4>
<p class="body">
Checks for illegal instantiations where a factory method is preferred.
</p>
<p class="body">
Rationale: Depending on the project, for some classes it might be preferable to
create instances through factory methods rather than calling the constructor.
</p>
<p class="body">
A simple example is the <span class="code">java.lang.Boolean</span> class. In
order to save memory and CPU cycles, it is preferable to use the predefined
constants <span class="code">
TRUE</span> and <span class="code">FALSE</span>. Constructor invocations should
be replaced by calls to <span class="code">Boolean.valueOf()</span>.
</p>
<p class="body">
Some extremely performance sensitive projects may require the use of factory
methods for other classes as well, to enforce the usage of number caches or
object pools.
</p>
<h4>Notes</h4>
<p class="body">
There is a limitation that it is currently not possible to specify array classes.
</p>
<table width="100%" border="1" cellpadding="5" class="body">
<tr class="header">
<th>name</th>
<th>description</th>
<th>type</th>
<th>default value</th>
</tr>
<tr>
<td>classes</td>
<td>classes that should not be instantiated</td>
<td><a href="property_types.html#stringSet">String Set</a></td>
<td>{}</td>
</tr>
</table>
<h4>Example</h4>
<p class="body">
To configure the check to find instantiations of java.lang.Boolean:
</p>
<pre class="body">
&lt;module name=&quot;IllegalInstantiation&quot;&gt;
&lt;property name=&quot;classes&quot; value=&quot;java.lang.Boolean&quot;/&gt;
&lt;/module&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="InnerAssignment"></a> <h2>InnerAssignment</h2> <h4>Description</h4>
<p class="body">
Checks for assignments in subexpressions, such as in <span class="code">String s
= Integer.toString(i = 2);</span>.
</p>
<p class="body">
Rationale: With the exception of <span class="code">for</span> iterators, all
assignments should occur in their own toplevel statement to increase readability.
With inner assignments like the above it is difficult to see all places where a
variable is set.
</p>
<h4>Properties</h4>
<table width="100%" border="1" cellpadding="5" class="body">
<tr class="header">
<th>name</th>
<th>description</th>
<th>type</th>
<th>default value</th>
</tr>
<tr>
<td>tokens</td>
<td>assignments to check</td>
<td>subset of tokens <a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#ASSIGN">ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BAND_ASSIGN">BAND_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BOR_ASSIGN">BOR_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BSR_ASSIGN">BSR_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BXOR_ASSIGN">BXOR_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#DIV_ASSIGN">DIV_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#MINUS_ASSIGN">MINUS_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#MOD_ASSIGN">MOD_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#PLUS_ASSIGN">PLUS_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#SL_ASSIGN">SL_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#SR_ASSIGN">SR_ASSIGN</a>,
<a
href="api/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#STAR_ASSIGN">STAR_ASSIGN</a></td>
<td>all tokens</td>
</tr>
</table>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;InnerAssignment&quot;/&gt;
</pre>
<p class="body">
To configure the check for only <span class="code">=</span>, <span class="code">
+=</span>, and <span class="code">-=</span> operators:
</p>
<pre class="body">
&lt;module name=&quot;InnerAssignment&quot;&gt;
&lt;property name=&quot;tokens&quot; value=&quot;ASSIGN,PLUS_ASSIGN,MINUS_ASSIGN&quot;/&gt;
&lt;/module&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="MagicNumber"></a> <h2>MagicNumber</h2> <h4>Description</h4>
<p class="body">
Checks that there are no &quot;magic numbers&quot;, where a
magic number is a numeric literal that is not defined as a
constant. By default, -1, 0, 1, and 2 are not considered to
be magic numbers.
</p>
<h4>Properties</h4>
<table width="100%" border="1" cellpadding="5" class="body">
<tr class="header">
<th>name</th>
<th>description</th>
<th>type</th>
<th>default value</th>
</tr>
<tr>
<td>tokens</td>
<td>tokens to check</td>
<td>subset of tokens NUM_DOUBLE, NUM_FLOAT, NUM_INT, NUM_LONG</td>
<td>all tokens</td>
</tr>
<tr>
<td>ignoreNumbers</td>
<td>non-magic numbers</td>
<td>list of numbers</td>
<td>-1, 0, 1, 2</td>
</tr>
</table>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;MagicNumber&quot;/&gt;
</pre>
<p class="body">
To configure the check so that it checks floating-point
numbers that are neither 0, 0.5, nor 1:
</p>
<pre class="body">
&lt;module name=&quot;MagicNumber&quot;&gt;
&lt;property name=&quot;tokens&quot; value=&quot;NUM_DOUBLE, NUM_FLOAT&quot;/&gt;
&lt;property name=&quot;ignoreNumbers&quot; value=&quot;0, 0.5, 1&quot;/&gt;
&lt;/module&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="MissingSwitchDefault"></a> <h2>MissingSwitchDefault</h2> <h4>Description</h4>
<p class="body">
Checks that switch statement has &quot;default&quot; clause.
</p>
<p class="body">
Rationale: It's usually a good idea to introduce a default case
in every switch statement. Even if the developer is sure that
all currently possible cases are covered, this should be
expressed in the default branch, e.g. by using an
assertion. This way the code is protected aginst later changes,
e.g. introduction of new types in an enumeration type.
</p>
<h4>Examples</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;MissingSwitchDefault&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="SimplifyBooleanExpression"></a> <h2>SimplifyBooleanExpression</h2>
<h4>Description</h4>
<p class="body">
Checks for overly complicated boolean expressions. Currently finds code like <span class="code">
if (b == true)</span>, <span class="code">b || true</span>, <span class="code">!false</span>, etc.
</p>
<p class="body">
Rationale: Complex boolean logic makes code hard to understand and maintain.
</p>
<h4>Example</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;SimplifyBooleanExpression&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
<!-- --> <a name="SimplifyBooleanReturn"></a> <h2>SimplifyBooleanReturn</h2> <h4>Description</h4>
<p class="body">
Checks for overly complicated boolean return statements. For example the following code
</p>
<pre class="body">
if (valid())
return false;
else
return true;
</pre>
<p class="body">
could be written as
</p>
<pre class="body">
return !valid();
</pre>
<p class="body">
The Idea for this Check has been shamelessly stolen
from the equivalent <a href="http://pmd.sourceforge.net">PMD</a> rule.
</p>
<h4>Example</h4>
<p class="body">
To configure the check:
</p>
<pre class="body">
&lt;module name=&quot;SimplifyBooleanReturn&quot;/&gt;
</pre>
<h4>Package</h4>
<p class="body">
com.puppycrawl.tools.checkstyle.checks
</p>
<h4>Parent Module</h4>
<p class="body">
<a href="config.html#treewalker">TreeWalker</a>
</p>
</td>
</tr>
</table>
<hr />
<div><a href="index.html">Back to the Checkstyle Home Page</a></div>
<p class="copyright">
Copyright &copy; 2002-2003 Oliver Burn. All rights Reserved.
</p>
</body>
</html>
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