Since Checkstyle 8.30


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="Checker">
  <module name="TreeWalker">
    <module name="AvoidDoubleBraceInitialization"/>

Which results in the following violations:

class Example1 {
  List<Integer> list1 = new ArrayList<>() { // violation
  List<String> list2 = new ArrayList<>() { // violation
    // comments and semicolons are ignored
  List<Object> list = new ArrayList<>() {
    // OK, as it is not double brace pattern
    private int field;
      add(new Object());

Example of Usage

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.



Parent Module