Question

This is my code for getting field values and annotation values, I placed the values into a map, however problem is there is a $this that is in the map.

Map doc = null;
        String kind = null;
        Class classObj = obj.getClass();
        Annotation[] annotations = classObj.getAnnotations();
        for (Annotation annotation : annotations) {
                Entity entityAnnotation = (Entity)annotation; 
                kind = entityAnnotation.name();
                if (entityAnnotation != null){
                        if (doc == null){
                            doc = new LinkedHashMap();
                        }
                        Field[] fields = classObj.getDeclaredFields();
                        for (Field field : fields){
                                annotations = field.getDeclaredAnnotations();
                                String value = null;
                                String fieldName = field.getName();
                                try {
                                        boolean access = field.isAccessible();
                                        field.setAccessible(true);
                                        Object fieldValue = field.get(obj); 
                                        doc.put(fieldName, fieldValue);
                                        field.setAccessible(access);
                                } catch (Exception e) {
                                        e.printStackTrace();
                                }                               
                                // Process fields with annotation
                                for(Annotation fieldAnnotation : annotations){
                                    if (annotation instanceof Id){
                                        Id idAnnotation = (Id) fieldAnnotation;
                                        log.info("Field name="+fieldName+" "+ value + " Annotation value: " + idAnnotation.value()); 
                                        doc.put("_id", value);
                                    }                                   
                                }
                        }                               
                }
        }

Test output:

Key=id value=id1
Key=name value=Eli
Key=age value=25
Key=this$0 value=org.goo.AnnotationTest@7f5227

Answer 1

The field this$0 is the reference to the outer class.

If you want to avoid this, make the class static. IMHO you should make nested class static where possible, partly for performance, but mostly for clarity. If this is not an option, you can ignore that field explicitly.

BTW: If you create a field called this$0 it will use the field this$$0 or this$$$0 or this$$$$0 etc instead.