Package com.puppycrawl.tools.checkstyle.checks.coding

Class AvoidDoubleBraceInitializationCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public class AvoidDoubleBraceInitializationCheck
extends AbstractCheck

    Detects double brace initialization.

    Rationale: Double brace initialization (set of Instance Initializers in class body) may look cool, but it is considered as anti-pattern and should be avoided. This is also can lead to a hard-to-detect memory leak, if the anonymous class instance is returned outside and other object(s) hold reference to it. Created anonymous class is not static, it holds an implicit reference to the outer class instance. See this blog post and article for more details. Check ignores any comments and semicolons in class body.

    To configure the check: 

     <module name="AvoidDoubleBraceInitialization"/>

    Which results in the following violations: 

     class MyClass {
     List<Integer> list1 = new ArrayList<>() { // violation
         {
             add(1);
         }
     };
     List<String> list2 = new ArrayList<>() { // violation
         ;
         // comments and semicolons are ignored
         {
             add("foo");
         }
     };
 }

    Check only looks for double brace initialization and it ignores cases where the anonymous class has fields or methods. Though these might create the same memory issues as double brace, the extra class members can produce side effects if changed incorrectly. 

     class MyClass {
     List<Object> list = new ArrayList<>() { // OK, not pure double brace pattern
         private int field;
         {
             add(new Object());
         }
     };
 }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • avoid.double.brace.init
    Since:
    8.30

    • Field Detail

      • MSG_KEY

        public static final java.lang.String MSG_KEY
        A key is pointing to the warning message text in "messages.properties" file.
        See Also:
        Constant Field Values

    • Constructor Detail

      • AvoidDoubleBraceInitializationCheck

        public AvoidDoubleBraceInitializationCheck()

    • Method Detail

      • getDefaultTokens

        public int[] getDefaultTokens()
        Description copied from class: AbstractCheck
        Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.
        Specified by:
        getDefaultTokens in class AbstractCheck
        Returns:
        the default tokens
        See Also:
        TokenTypes

      • getAcceptableTokens

        public int[] getAcceptableTokens()
        Description copied from class: AbstractCheck
        The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.
        Specified by:
        getAcceptableTokens in class AbstractCheck
        Returns:
        the token set this check is designed for.
        See Also:
        TokenTypes

      • getRequiredTokens

        public int[] getRequiredTokens()
        Description copied from class: AbstractCheck
        The tokens that this check must be registered for.
        Specified by:
        getRequiredTokens in class AbstractCheck
        Returns:
        the token set this must be registered for.
        See Also:
        TokenTypes