Hi,
If you are using a calculation done inside the java action you can choose to return that value and just use a change action in the microflow to change the object attribute. If you are looking for a different method/explanation - please provide a little more information for me to go with.
Hi Menagapriya,
If you want to change your object inside your java action, you can use the change method. Here is the link to the runtime documentation.
https://apidocs.mendix.com/7/runtime/
Hope this helps!