Michał Herman Michał Herman - 4 months ago 16
Java Question

Get all fields (even private and inherited) from class

I am making university project.

I need to get all fields from class. Even private and inherited. I tried to get all declared fields and then cast to super class and repeat.
Fragment of my code:

private void listAllFields(Object obj) {
List<Field> fieldList = new ArrayList<Field>();
while (obj != null) {
obj = obj.getClass().getSuperclass().cast(obj);
// rest of code

But it does not work.
after casting is still the same class (not superclass).

I will appreciate any help how to fix casting problem, or how to retrieve these fields in different way.


Problem is not to gain access to fields, but to get names of fields!

I manages it that way:

private void listAllFields(Object obj) {
List<Field> fieldList = new ArrayList<Field>();
Class tmpClass = obj.getClass();
while (tmpClass != null) {
fieldList.addAll(Arrays.asList(tmpClass .getDeclaredFields()));
tmpClass = tmpClass .getSuperclass();
// rest of code

obj = obj.getClass().getSuperclass().cast(obj);

This line does not do what you expect it to do. Casting an Object does not actually change it, it just tells the compiler to treat it as something else.

E.g. you can cast a List to a Collection, but it will still remain a List.

However, looping up through the super classes to access fields works fine without casting:

Class<?> current = yourClass;
while(current.getSuperclass()!=null){ // we don't want to process Object.class
    // do something with current's fields
    current = current.getSuperclass();

BTW, if you have access to the Spring Framework, there is a handy method for looping through the fields of a class and all super classes:
ReflectionUtils.doWithFields(baseClass, FieldCallback)
(also see this previous answer of mine: Access to private inherited fields via reflection in Java)