Class IllegalTypeCheck

Checks that particular classes or interfaces are never used.

Rationale: Helps reduce coupling on concrete classes.

For additional restriction of type usage see also: IllegalInstantiation, IllegalImport

It is possible to set illegal class names via short or canonical name. Specifying illegal type invokes analyzing imports and Check puts violations at corresponding declarations (of variables, methods or parameters). This helps to avoid ambiguous cases, e.g.: java.awt.List was set as illegal class name, then, code like:

 import java.util.List;
 ...
 List list; //No violation here
 

will be ok.

In most cases it's justified to put following classes to illegalClassNames:

• GregorianCalendar
• Hashtable
• ArrayList
• LinkedList
• Vector

as methods that are differ from interface methods are rarely used, so in most cases user will benefit from checking for them.

• Property validateAbstractClassNames - Control whether to validate abstract class names. Type is boolean. Default value is false.
• Property illegalClassNames - Specify classes that should not be used as types in variable declarations, return values or parameters. Type is java.lang.String[]. Default value is HashMap, HashSet, LinkedHashMap, LinkedHashSet, TreeMap, TreeSet, java.util.HashMap, java.util.HashSet, java.util.LinkedHashMap, java.util.LinkedHashSet, java.util.TreeMap, java.util.TreeSet.
• Property legalAbstractClassNames - Define abstract classes that may be used as types. Type is java.lang.String[]. Default value is "".
• Property ignoredMethodNames - Specify methods that should not be checked. Type is java.lang.String[]. Default value is getEnvironment, getInitialContext.
• Property illegalAbstractClassNameFormat - Specify RegExp for illegal abstract class names. Type is java.util.regex.Pattern. Default value is "^(.*[.])?Abstract.*$".
• Property memberModifiers - Control whether to check only methods and fields with any of the specified modifiers. This property does not affect method calls nor method references. Type is java.lang.String[]. Validation type is tokenTypesSet. Default value is no tokens.
• Property tokens - tokens to check Type is java.lang.String[]. Validation type is tokenSet. Default value is: ANNOTATION_FIELD_DEF, CLASS_DEF, INTERFACE_DEF, METHOD_CALL, METHOD_DEF, METHOD_REF, PARAMETER_DEF, VARIABLE_DEF, PATTERN_VARIABLE_DEF, RECORD_DEF, RECORD_COMPONENT_DEF.

To configure the default check:

 <module name="IllegalType"/>
 

 public class Test extends TreeSet { // violation
   public <T extends java.util.HashSet> void method() { // violation

     LinkedHashMap<Integer, String> lhmap =
     new LinkedHashMap<Integer, String>(); // violation
     TreeMap<Integer, String> treemap =
     new TreeMap<Integer, String>(); // violation
     Test t; // OK
     HashMap<String, String> hmap; // violation
     Queue<Integer> intqueue; // OK

     java.lang.IllegalArgumentException illegalex; // OK
     java.util.TreeSet treeset; // violation
   }

 }
 

To configure the Check so that particular tokens are checked:

 <module name="IllegalType">
   <property name="tokens" value="METHOD_DEF"/>
 </module>
 

 public class Test extends TreeSet { // OK
   public <T extends java.util.HashSet> void method() { // violation
     LinkedHashMap<Integer, String> lhmap =
     new LinkedHashMap<Integer, String>(); // OK

     java.lang.IllegalArgumentException illegalex; // OK
     java.util.TreeSet treeset; // Ok
   }

   public <T extends java.util.HashSet> void typeParam(T t) {} // violation

   public void fullName(TreeSet a) {} // OK

 }
 

To configure the Check so that it ignores function() methods:

 <module name="IllegalType">
   <property name="ignoredMethodNames" value="function"/>
 </module>
 

 public class Test {
   public HashMap<String, String> function() { // OK
     // code
   }

   public HashMap<String, String> function1() { // violation
     // code
   }
 }
 

To configure the Check so that it validates abstract class names:

  <module name="IllegalType">
    <property name="validateAbstractClassNames" value="true"/>
    <property name="illegalAbstractClassNameFormat" value="Gitt"/>
  </module>
 

 class Test extends Gitter { // violation
 }

 class Test1 extends Github { // OK
 }
 

To configure the Check so that it verifies only public, protected or static methods and fields:

 <module name="IllegalType">
   <property name="memberModifiers" value="LITERAL_PUBLIC,
    LITERAL_PROTECTED, LITERAL_STATIC"/>
 </module>
 

 public class Test {
   public HashMap<String, String> function1() { // violation
     // code
   }

   private HashMap<String, String> function2() { // OK
     // code
   }

   protected HashMap<Integer, String> function3() { // violation
     // code
   }

   public static TreeMap<Integer, String> function4() { // violation
     // code
   }

 }
 

To configure the check so that it verifies usage of types Boolean and Foo:

 <module name="IllegalType">
           <property name="illegalClassNames" value="Boolean, Foo"/>
 </module>
 

 public class Test {

   public Set<Boolean> set; // violation
   public java.util.List<Map<Boolean, Foo>> list; // violation

   private void method(List<Foo> list, Boolean value) { // violation
     SomeType.<Boolean>foo(); // violation
     final Consumer<Foo> consumer = Foo<Boolean>::foo; // violation
   }

   public <T extends Boolean, U extends Serializable> void typeParam(T a) {} // violation

   public void fullName(java.util.ArrayList<? super Boolean> a) {} // violation

   public abstract Set<Boolean> shortName(Set<? super Boolean> a); // violation

   public Set<? extends Foo> typeArgument() { // violation
     return new TreeSet<Foo<Boolean>>();
   }

 }
 

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• illegal.type