Source code: com/puppycrawl/tools/checkstyle/checks/design/InputMutableException.java

   package com.puppycrawl.tools.checkstyle.checks.design;
   
   public class InputMutableException {
       public class FooException {
           private final int _finalErrorCode;
           private int _errorCode = 1;
   
           public FooException() {
               _finalErrorCode = 1;
          }
  
          public class FooExceptionThisIsNot {
              private final int _finalErrorCode;
              private int _errorCode = 1;
  
              public FooExceptionThisIsNot() {
                  _finalErrorCode = 1;
              }
          }
      }
  
      public class FooError {
          private int _errorCode;
      }
  }