src/xdocs/config_design.xml - platform/external/checkstyle - Git at Google

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   xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">

   <head>
     <title>Class Design</title>
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   <body>
     <section name="Content">
       <macro name="toc">
         <param name="fromDepth" value="1"/>
         <param name="toDepth" value="1"/>
       </macro>
     </section>

     <section name="DesignForExtension">
       <subsection name="Description">
         <p>Since Checkstyle 3.1</p>
         <p>
           The check finds classes that are designed for extension (subclass creation).
         </p>
         <p>
           Nothing wrong could be with founded classes.
           This check makes sense only for library projects (not application projects)
           which care of ideal OOP-design to make sure that class works in all cases even misusage.
           Even in library projects this check most likely will find classes that are designed
           for extension by somebody. User needs to use suppressions extensively to got a benefit from
           this check, and keep in suppressions all confirmed/known classes that are deigned for
           inheritance intentionally to let the check catch only new classes, and bring this to
           team/user attention.
         </p>
         <p>
          ATTENTION: Only user can decide whether a class is designed for extension or not.
          The check just shows all classes which are possibly designed for extension.
          If smth inappropriate is found please use suppression.
         </p>
         <p>
          ATTENTION: If the method which can be overridden in a subclass has a javadoc comment
          (a good practice is to explain its self-use of overridable methods) the check will not
          rise a violation. The violation can also be skipped if the method which can be overridden
          in a subclass has one or more annotations that are specified in ignoredAnnotations
          option. Note, that by default @Override annotation is not included in the
          ignoredAnnotations set as in a subclass the method which has the annotation can also be
          overridden in its subclass.
         </p>
          <p>
           Problem is described at "Effective Java, 2nd Edition by Josh Bloch" book, chapter "Item 17: Design and document for inheritance or else prohibit it".
         </p>
         <p>
           Some quotes from book:
         </p>
         <blockquote>The class must document its self-use of overridable methods.
 By convention, a method that invokes overridable methods contains a description
 of these invocations at the end of its documentation comment. The description
 begins with the phrase “This implementation.”
         </blockquote>
         <blockquote>The best solution to this problem is to prohibit subclassing in classes that
 are not designed and documented to be safely subclassed.
         </blockquote>
         <blockquote>If a concrete class does not implement a standard interface, then you may
 inconvenience some programmers by prohibiting inheritance. If you feel that you
 must allow inheritance from such a class, one reasonable approach is to ensure
 that the class never invokes any of its overridable methods and to document this
 fact. In other words, eliminate the class’s self-use of overridable methods entirely.
 In doing so, you’ll create a class that is reasonably safe to subclass. Overriding a
 method will never affect the behavior of any other method.
         </blockquote>
         <p>
           The check finds classes that have overridable methods (public or protected methods
           that are non-static, not-final, non-abstract) and have non-empty implementation.
         </p>

         <p>
           Rationale: This library design style protects superclasses against
           being broken by subclasses. The downside is that subclasses are
           limited in their flexibility, in particular they cannot prevent
           execution of code in the superclass, but that also means that
           subclasses cannot corrupt the state of the superclass by forgetting
           to call the superclass's method.
         </p>
         <p>
           More specifically,
           it enforces a programming style where superclasses provide empty
           "hooks" that can be implemented by subclasses.
         </p>
         <p>
           Example of code that cause violation as it is designed for extension:
         </p>
         <source>
 public abstract class Plant {
     private String roots;
     private String trunk;

     protected void validate() {
       if (roots == null) throw new IllegalArgumentException("No roots!");
       if (trunk == null) throw new IllegalArgumentException("No trunk!");
     }

     public abstract void grow();
 }

 public class Tree extends Plant {
     private List leaves;

     @Overrides
     protected void validate() {
       super.validate();
       if (leaves == null) throw new IllegalArgumentException("No leaves!");
     }

     public void grow() {
       validate();
     }
 }
         </source>
         <p>
           Example of code without violation:
         </p>
         <source>
 public abstract class Plant {
     private String roots;
     private String trunk;

     private void validate() {
         if (roots == null) throw new IllegalArgumentException("No roots!");
         if (trunk == null) throw new IllegalArgumentException("No trunk!");
         validateEx();
     }

     protected void validateEx() { }

     public abstract void grow();
 }
         </source>
       </subsection>

       <subsection name="Properties">
             <table>
                 <tr>
                     <th>name</th>
                     <th>description</th>
                     <th>type</th>
                     <th>default value</th>
                     <th>since</th>
                 </tr>
                 <tr>
                     <td>ignoredAnnotations</td>
                     <td>
                         Annotations which allow the check to skip the method from validation.
                     </td>
                     <td><a href="property_types.html#stringSet">String Set</a></td>
                     <td><code>Test, Before, After, BeforeClass, AfterClass</code></td>
                     <td>7.2</td>
                 </tr>
             </table>
         </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>

         <source>
 &lt;module name=&quot;DesignForExtension&quot;/&gt;
         </source>

         <p>
           To configure the check to allow methods which have @Override and @Test annotations to be
           designed for extension.
         </p>

         <source>
 &lt;module name=&quot;DesignForExtension&quot;&gt;
   &lt;property name=&quot;ignoredAnnotations&quot; value=&quot;Override, Test&quot;/&gt;
 &lt;/module&gt;
         </source>

         <source>
 public class A extends B {
   @Override
   public int foo() {
     return 2;
   }

   public int foo2() {return 8;} // violation
 }

 public class B {
   /**
    * This implementation ...
      @return some int value.
    */
   public int foo() {
     return 1;
   }

   public int foo3() {return 3;} // violation
 }

 public class FooTest {
   @Test
   public void testFoo() {
      final B b = new A();
      assertEquals(2, b.foo());
   }

   public int foo4() {return 4;} // violation
 }
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources+filename%3Asun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+DesignForExtension">
             Sun Style</a>
           </li>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+DesignForExtension">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22design.forExtension%22">
             design.forExtension</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="FinalClass">
       <subsection name="Description">
         <p>Since Checkstyle 3.1</p>
         <p>
           Checks that a class which has only private constructors is declared
           as final. Doesn't check for classes nested in interfaces
           or annotations, as they are always <code>final</code> there.
         </p>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>
         <source>
 &lt;module name=&quot;FinalClass&quot;/&gt;
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources+filename%3Asun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+FinalClass">
             Sun Style</a>
           </li>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+FinalClass">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22final.class%22">
             final.class</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="HideUtilityClassConstructor">
       <subsection name="Description">
         <p>Since Checkstyle 3.1</p>
         <p>
           Makes sure that utility classes (classes that contain only static
           methods or fields in their API) do not have a public constructor.
         </p>

         <p>
           Rationale: Instantiating utility classes does not make sense.  Hence
           the constructors should either be private or (if you want to allow
           subclassing) protected. A common mistake is forgetting to hide the
           default constructor.
         </p>

         <p>
           If you make the constructor protected you may want to consider the
           following constructor implementation technique to disallow
           instantiating subclasses:
         </p>

         <source>
 public class StringUtils // not final to allow subclassing
 {
     protected StringUtils() {
         // prevents calls from subclass
         throw new UnsupportedOperationException();
     }

     public static int count(char c, String s) {
         // ...
     }
 }
         </source>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>
         <source>
 &lt;module name=&quot;HideUtilityClassConstructor&quot;/&gt;
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources+filename%3Asun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+HideUtilityClassConstructor">
             Sun Style</a>
           </li>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+HideUtilityClassConstructor">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22hide.utility.class%22">
             hide.utility.class</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="InnerTypeLast">
       <subsection name="Description">
         <p>Since Checkstyle 5.2</p>
         <p>
           Check nested (inner) classes/interfaces are declared at the
           bottom of the class after all method and field declarations.
         </p>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>
         <source>
 &lt;module name=&quot;InnerTypeLast&quot;/&gt;
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+InnerTypeLast">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22arrangement.members.before.inner%22">
             arrangement.members.before.inner</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="InterfaceIsType">
       <subsection name="Description">
         <p>Since Checkstyle 3.1</p>
         <p>
           Implements Joshua Bloch, Effective Java, Item 17 - Use Interfaces only to
           define types.
         </p>

         <p>
           According to Bloch, an interface should describe a <em>type</em>.
           It is therefore inappropriate to define an interface that does not
           contain any methods but only constants. The Standard class <a
           href="https://docs.oracle.com/javase/8/docs/api/javax/swing/SwingConstants.html">javax.swing.SwingConstants</a>
           is an example of a class that would be flagged by this check.
         </p>

         <p>
           The check can be configured to also disallow marker interfaces like
           <code>java.io.Serializable</code>, that do not contain methods or
           constants at all.
         </p>
       </subsection>

       <subsection name="Properties">
         <table>
           <tr>
             <th>name</th>
             <th>description</th>
             <th>type</th>
             <th>default value</th>
             <th>since</th>
           </tr>
           <tr>
             <td>allowMarkerInterfaces</td>
             <td>
               Controls whether marker interfaces like Serializable are
               allowed.
             </td>
             <td><a href="property_types.html#boolean">Boolean</a></td>
             <td><code>true</code></td>
             <td>3.1</td>
           </tr>
         </table>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>
         <source>
 &lt;module name=&quot;InterfaceIsType&quot;/&gt;
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources+filename%3Asun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+InterfaceIsType">
             Sun Style</a>
           </li>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+InterfaceIsType">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22interface.type%22">
             interface.type</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="MutableException">
       <subsection name="Description">
         <p>Since Checkstyle 3.2</p>
         <p>
           Ensures that exception classes (classes with names conforming to some regular
           expression and explicitly extending classes with names conforming to other
           regular expression) are immutable, that is, that they have only final fields.
         </p>

         <p>
           The current algorithm is very simple: it checks that all members of
           exception are final.  The user can still mutate an exception's instance
           (e.g. Throwable has a method called <code>setStackTrace</code>
           which changes the exception's stack trace).  But, at least, all information
           provided by this exception type is unchangeable.
         </p>

         <p>
           Rationale: Exception instances should represent an error
           condition. Having non final fields not only allows the state to be
           modified by accident and therefore mask the original condition but
           also allows developers to accidentally forget to set the initial state.
           In both cases, code catching the exception could draw incorrect
           conclusions based on the state.
         </p>
       </subsection>

       <subsection name="Properties">
         <table>
           <tr>
             <th>name</th>
             <th>description</th>
             <th>type</th>
             <th>default value</th>
             <th>since</th>
           </tr>
           <tr>
             <td>format</td>
             <td>pattern for exception class names</td>
             <td><a href="property_types.html#regexp">Regular Expression</a></td>
             <td><code>"^.*Exception$|^.*Error$|^.*Throwable$"</code></td>
             <td>3.2</td>
           </tr>
           <tr>
             <td>extendedClassNameFormat</td>
             <td>pattern for extended class names</td>
             <td><a href="property_types.html#regexp">Regular Expression</a></td>
             <td><code>"^.*Exception$|^.*Error$|^.*Throwable$"</code></td>
             <td>6.2</td>
           </tr>
         </table>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>
         <source>
 &lt;module name=&quot;MutableException&quot;/&gt;
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+MutableException">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22mutable.exception%22">
             mutable.exception</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="OneTopLevelClass">
       <subsection name="Description">
         <p>Since Checkstyle 5.8</p>
         <p>
           Checks that each top-level class, interface or
           enum resides in a source file of its own.
           Official description of a 'top-level' term:<a
           href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-7.html#jls-7.6">7.6. Top Level Type Declarations</a>.
           If file doesn't contains public class, enum or interface,
           top-level type is the first type in file.
         </p>
       </subsection>

       <subsection name="Examples">
         <p>
           An example of check's configuration:
         </p>
         <source>
 &lt;module name="OneTopLevelClass"/&gt;
         </source>
         <p>
           <b>ATTENTION:</b> This Check does not support customization of validated tokens, so do not use the "tokens" property.
         </p>
         <p>
           An example of code with violations:
         </p>
         <source>
 public class Foo{
     //methods
 }

 class Foo2{
     //methods
 }
         </source>
         <p>
           An example of code without public top-level type:
         </p>
         <source>
 class Foo{ // top-level class
     //methods
 }

 class Foo2{
     //methods
 }
         </source>
         <p>
           An example of code without violations:
         </p>
         <source>
 public class Foo{
     //methods
 }
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources+filename%3Agoogle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+OneTopLevelClass">
             Google Style</a>
           </li>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+OneTopLevelClass">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22one.top.level.class%22">
             one.top.level.class</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="ThrowsCount">
       <subsection name="Description">
         <p>Since Checkstyle 3.2</p>
         <p>
           Restricts throws statements to a specified count (4 by default).
           Methods with "Override" or "java.lang.Override" annotation are skipped
           from validation as current class cannot change signature of these methods.
         </p>

         <p>
           Rationale: Exceptions form part of a method's interface. Declaring a
           method to throw too many differently rooted exceptions makes
           exception handling onerous and leads to poor programming practices
           such as writing code like <code>catch(Exception ex)</code>.
           4 is the empirical value which is based on reports that we had for
           the ThrowsCountCheck over big projects such as OpenJDK.
           This check also forces developers to put exceptions into a hierarchy
           such that in the simplest case, only one type of exception need be
           checked for by a caller but any subclasses can be caught specifically
           if necessary.For more information on rules for the exceptions and
           their issues, see Effective Java: Programming Language Guide
           Second Edition by Joshua Bloch pages 264-273.
         </p>

         <p>
           <b>ignorePrivateMethods</b> - allows to skip private methods as they do
           not cause problems for other classes.
         </p>
       </subsection>

       <subsection name="Properties">
         <table>
           <tr>
             <th>name</th>
             <th>description</th>
             <th>type</th>
             <th>default value</th>
             <th>since</th>
           </tr>
           <tr>
             <td>max</td>
             <td>maximum allowed number of throws statements</td>
             <td><a href="property_types.html#integer">Integer</a></td>
             <td><code>4</code></td>
             <td>3.2</td>
           </tr>
           <tr>
             <td>ignorePrivateMethods</td>
             <td>whether private methods must be ignored</td>
             <td><a href="property_types.html#boolean">Boolean</a></td>
             <td><code>true</code></td>
             <td>6.7</td>
           </tr>
         </table>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check so that it doesn't allow more than two throws
           per method:
         </p>
         <source>
 &lt;module name=&quot;ThrowsCount&quot;&gt;
     &lt;property name=&quot;max&quot; value=&quot;2&quot;/&gt;
 &lt;/module&gt;
         </source>

         <p>
           To configure the check so that it doesn't skip private methods:
         </p>
         <source>
 &lt;module name=&quot;ThrowsCount&quot;&gt;
     &lt;property name=&quot;ignorePrivateMethods&quot; value=&quot;false&quot;/&gt;
 &lt;/module&gt;
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+ThrowsCount">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22throws.count%22">
             throws.count</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>

     <section name="VisibilityModifier">
       <subsection name="Description">
         <p>Since Checkstyle 3.0</p>
         <p>
           Checks visibility of class members. Only static final, immutable or annotated
           by specified annotation members may be public; other class members must be private
           unless the property <code>protectedAllowed</code> or <code>packageAllowed</code> is set.
         </p>

         <p>
           Public members are not flagged if the name matches the public
           member regular expression (contains <code>"^serialVersionUID$"</code> by default).
         </p>
         <p>Note that
           Checkstyle 2 used to include <code>"^f[A-Z][a-zA-Z0-9]*$"</code> in the default
           pattern to allow names used in container-managed persistence for Enterprise JavaBeans (EJB) 1.1 with the default settings.
           With EJB 2.0 it is no longer necessary to have public access
           for persistent fields, so the default has been changed.
         </p>

         <p>
           Rationale: Enforce encapsulation.
         </p>
         <p>
           Check also has options making it less strict:
         </p>
         <p>
           <b>ignoreAnnotationCanonicalNames</b> - the list of annotations which ignore variables
           in consideration. If user will provide short annotation name that type will match to any
           named the same type without consideration of package
         </p>
         <p>
           <b>allowPublicFinalFields</b> - which allows public final fields.
           Default value is <b>false</b>
         </p>
         <p>
           <b>allowPublicImmutableFields</b> - which allows immutable fields to be declared as
           public if defined in final class. Default value is <b>false</b>
         </p>
         <p>
           Field is known to be immutable if:
           - It's declared as final
           - Has either a primitive type or instance of class user defined to be immutable
           (such as String, ImmutableCollection from Guava and etc)
         </p>
         <p>
           Classes known to be immutable are listed in <b>immutableClassCanonicalNames</b> by their
           <b>canonical</b> names.
         </p>
         <p>
           Rationale: Forcing all fields of class to have private modified by default is good
           in most cases, but in some cases it drawbacks in too much boilerplate get/set code.
           One of such cases are immutable classes.
         </p>
         <p>
           <b>Restriction</b>: Check doesn't check if class is immutable, there's no
           checking if accessory methods are missing and all fields are immutable, we only check
           <b>if current field is immutable or final</b>. Under the flag
           <b>allowPublicImmutableFields</b>, the enclosing class must also be final, to encourage
           immutability. Under the flag <b>allowPublicFinalFields</b>, the final modifier on
           the enclosing class is optional.
         </p>
         <p>
           Star imports are out of scope of this Check. So if one of type imported via
           <b>star import</b> collides with user specified one by its short name -
           there won't be Check's violation.
         </p>
       </subsection>

       <subsection name="Properties">
         <table>
           <tr>
             <th>name</th>
             <th>description</th>
             <th>type</th>
             <th>default value</th>
             <th>since</th>
           </tr>
           <tr>
             <td>packageAllowed</td>
             <td>whether package visible members are allowed</td>
             <td><a href="property_types.html#boolean">Boolean</a></td>
             <td><code>false</code></td>
             <td>3.0</td>
           </tr>
           <tr>
             <td>protectedAllowed</td>
             <td>whether protected members are allowed</td>
             <td><a href="property_types.html#boolean">Boolean</a></td>
             <td><code>false</code></td>
             <td>3.0</td>
           </tr>
           <tr>
             <td>publicMemberPattern</td>
             <td>pattern for public members that should be ignored</td>
             <td><a href="property_types.html#regexp">Regular Expression</a></td>
             <td><code>"^serialVersionUID$"</code></td>
             <td>3.0</td>
           </tr>
           <tr>
             <td>allowPublicFinalFields</td>
             <td>allows public final fields</td>
             <td><a href="property_types.html#boolean">Boolean</a></td>
             <td><code>false</code></td>
             <td>7.0</td>
           </tr>
           <tr>
             <td>allowPublicImmutableFields</td>
             <td>allows immutable fields to be declared as public if defined in final class</td>
             <td><a href="property_types.html#boolean">Boolean</a></td>
             <td><code>false</code></td>
             <td>6.4</td>
           </tr>
           <tr>
             <td>immutableClassCanonicalNames</td>
             <td>immutable classes canonical names</td>
             <td><a href="property_types.html#stringSet">String Set</a></td>
             <td>java.lang.String, java.lang.Integer, java.lang.Byte, java.lang.Character,
             java.lang.Short, java.lang.Boolean, java.lang.Long, java.lang.Double, java.lang.Float,
             java.lang.StackTraceElement, java.math.BigInteger, java.math.BigDecimal, java.io.File,
             java.util.Locale, java.util.UUID, java.net.URL, java.net.URI,
             java.net.Inet4Address, java.net.Inet6Address, java.net.InetSocketAddress,</td>
             <td>6.4.1</td>
           </tr>
           <tr>
             <td>ignoreAnnotationCanonicalNames</td>
             <td>ignore annotations canonical names</td>
             <td><a href="property_types.html#stringSet">String Set</a></td>
             <td>org.junit.Rule, org.junit.ClassRule, com.google.common.annotations.VisibleForTesting</td>
             <td>6.5</td>
           </tr>
         </table>
       </subsection>

       <subsection name="Examples">
         <p>
           To configure the check:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;/&gt;
         </source>

         <p>
           To configure the check so that it allows package visible members:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
     &lt;property name=&quot;packageAllowed&quot; value=&quot;true&quot;/&gt;
 &lt;/module&gt;
         </source>

         <p>
           To configure the check so that it allows no public members:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
     &lt;property name=&quot;publicMemberPattern&quot; value=&quot;^$&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           To configure the Check so that it allows public immutable fields
           (mostly for immutable classes):
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
     &lt;property name=&quot;allowPublicImmutableFields&quot; value=&quot;true&quot;/&gt;
  &lt;/module&gt;
         </source>
         <p>
           Example of allowed public immutable fields:
         </p>
         <source>
 public class ImmutableClass
 {
     public final ImmutableSet&lt;String&gt; includes; // No warning
     public final ImmutableSet&lt;String&gt; excludes; // No warning
     public final java.lang.String notes; // No warning
     public final BigDecimal value; // No warning

     public ImmutableClass(Collection&lt;String&gt; includes, Collection&lt;String&gt; excludes,
                  BigDecimal value, String notes)
     {
         this.includes = ImmutableSet.copyOf(includes);
         this.excludes = ImmutableSet.copyOf(excludes);
         this.value = value;
         this.notes = notes;
     }
 }
         </source>
         <p>
           To configure the Check in order to allow user specified immutable class names:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
     &lt;property name=&quot;allowPublicImmutableFields&quot; value=&quot;true&quot;/&gt;
     &lt;property name=&quot;immutableClassCanonicalNames&quot; value=&quot;
     com.google.common.collect.ImmutableSet&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           Example of allowed public immutable fields:
         </p>
         <source>
 public class ImmutableClass
 {
     public final ImmutableSet&lt;String&gt; includes; // No warning
     public final ImmutableSet&lt;String&gt; excludes; // No warning
     public final java.lang.String notes; // Warning here because
                                          //'java.lang.String' wasn't specified as allowed class
     public final int someValue; // No warning

     public ImmutableClass(Collection&lt;String&gt; includes, Collection&lt;String&gt; excludes,
                  String notes, int someValue)
     {
         this.includes = ImmutableSet.copyOf(includes);
         this.excludes = ImmutableSet.copyOf(excludes);
         this.value = value;
         this.notes = notes;
         this.someValue = someValue;
     }
 }
         </source>

         <p>
           Note, if allowPublicImmutableFields is set to true, the check will also check whether
           generic type parameters are immutable. If at least one generic type parameter is mutable,
           there will be a violation.
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
   &lt;property name=&quot;allowPublicImmutableFields&quot; value=&quot;true&quot;/&gt;
   &lt;property name=&quot;immutableClassCanonicalNames&quot; value=&quot;
   com.google.common.collect.ImmutableSet, com.google.common.collect.ImmutableMap,java.lang.String&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           Example of how the check works:
         </p>
         <source>
 public final class Test {
     public final String s;
     public final ImmutableSet&lt;String&gt; names;
     public final ImmutableSet&lt;Object&gt; objects; // violation (Object class is mutable)
     public final ImmutableMap&lt;String, Object&gt; links; // violation (Object class is mutable)

     public Test() {
         s = "Hello!";
         names = ImmutableSet.of();
         objects = ImmutableSet.of();
         links = ImmutableMap.of();
     }
 }
         </source>
         <p>
           To configure the Check passing fields annotated with @com.annotation.CustomAnnotation:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
   &lt;property name=&quot;ignoreAnnotationCanonicalNames&quot; value=
   &quot;com.annotation.CustomAnnotation&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           Example of allowed field:
         </p>
         <source>
 class SomeClass
 {
     @com.annotation.CustomAnnotation
     String annotatedString; // no warning
     @CustomAnnotation
     String shortCustomAnnotated; // no warning
 }
         </source>

         <p>
           To configure the Check passing fields annotated with @org.junit.Rule, @org.junit.ClassRule and
           @com.google.common.annotations.VisibleForTesting annotations:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;/&gt;
         </source>
         <p>
           Example of allowed fields:
         </p>
         <source>
 class SomeClass
 {
     @org.junit.Rule
     public TemporaryFolder publicJUnitRule = new TemporaryFolder(); // no warning
     @org.junit.ClassRule
     public static TemporaryFolder publicJUnitClassRule = new TemporaryFolder(); // no warning
     @com.google.common.annotations.VisibleForTesting
     public String testString = ""; // no warning
 }
         </source>

         <p>
           To configure the Check passing fields annotated with short annotation name:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
   &lt;property name=&quot;ignoreAnnotationCanonicalNames&quot;
   value=&quot;CustomAnnotation&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           Example of allowed fields:
         </p>
         <source>
 class SomeClass
 {
     @CustomAnnotation
     String customAnnotated; // no warning
     @com.annotation.CustomAnnotation
     String customAnnotated1; // no warning
     @mypackage.annotation.CustomAnnotation
     String customAnnotatedAnotherPackage; // another package but short name matches
                                           // so no violation
 }
         </source>

         <p>
           To understand the difference between allowPublicImmutableFields and
           allowPublicFinalFields options, please, study the following examples.
         </p>
         <p>
            1) To configure the check to use only 'allowPublicImmutableFields' option:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
   &lt;property name=&quot;allowPublicImmutableFields&quot; value=&quot;true&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           Code example:
         </p>
         <source>
 public class InputPublicImmutable {
   public final int someIntValue; // violation
   public final ImmutableSet&lt;String&gt; includes; // violation
   public final java.lang.String notes; // violation
   public final BigDecimal value; // violation
   public final List list; // violation

   public InputPublicImmutable(Collection&lt;String&gt; includes,
         BigDecimal value, String notes, int someValue, List l) {
     this.includes = ImmutableSet.copyOf(includes);
     this.value = value;
     this.notes = notes;
     this.someIntValue = someValue;
     this.list = l;
   }
 }
         </source>
         <p>
           2) To configure the check to use only 'allowPublicFinalFields' option:
         </p>
         <source>
 &lt;module name=&quot;VisibilityModifier&quot;&gt;
   &lt;property name=&quot;allowPublicFinalFields&quot; value=&quot;true&quot;/&gt;
 &lt;/module&gt;
         </source>
         <p>
           Code example:
         </p>
         <source>
 public class InputPublicImmutable {
   public final int someIntValue;
   public final ImmutableSet&lt;String&gt; includes;
   public final java.lang.String notes;
   public final BigDecimal value;
   public final List list;

   public InputPublicImmutable(Collection&lt;String&gt; includes,
         BigDecimal value, String notes, int someValue, List l) {
     this.includes = ImmutableSet.copyOf(includes);
     this.value = value;
     this.notes = notes;
     this.someIntValue = someValue;
     this.list = l;
   }
 }
         </source>
       </subsection>

       <subsection name="Example of Usage">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources+filename%3Asun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+VisibilityModifier">
             Sun Style</a>
           </li>
           <li>
             <a href="https://github.com/search?q=path%3Aconfig+filename%3Acheckstyle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+VisibilityModifier">
             Checkstyle Style</a>
           </li>
         </ul>
       </subsection>

       <subsection name="Error Messages">
         <ul>
           <li>
             <a href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%2Fcom%2Fpuppycrawl%2Ftools%2Fcheckstyle%2Fchecks%2Fdesign+filename%3Amessages*.properties+repo%3Acheckstyle%2Fcheckstyle+%22variable.notPrivate%22">
             variable.notPrivate</a>
           </li>
         </ul>
         <p>
           All messages can be customized if the default message doesn't suit you.
           Please <a href="config.html#Custom_messages">see the documentation</a> to learn how to.
         </p>
       </subsection>

       <subsection name="Package">
         <p>
           com.puppycrawl.tools.checkstyle.checks.design
         </p>
       </subsection>

       <subsection name="Parent Module">
         <p>
           <a href="config.html#TreeWalker">TreeWalker</a>
         </p>
       </subsection>
     </section>
   </body>
 </document>