Java reflection get all private fields

Question

I wonder is there a way to get all private fields of some class in java and their type.

For example lets suppose I have a class

class SomeClass {
            


        

Answer 1

Check if a Field is private

You could filter the Fields using Modifier.isPrivate:

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
// ...
Field field = null;
// retrieve the field in some way
// ...
Modifier.isPrivate(field.getModifiers())

on a single Field object which returns true if the field is private

---

Collect all Fields of a class

To collect the all the Fields use:

1) If you need only the fields of the the class without the fields taken from the class hierarchy you could simply use:

Field[] fields = SomeClass.class.getDeclaredFields();

2) If you don't want to reinvent the wheel and get all the fields of a class hierarchy you could rely upon Apache Commons Lang version 3.2+ which provides FieldUtils.getAllFieldsList:

import java.lang.reflect.Field;
import java.util.AbstractCollection;
import java.util.AbstractList;
import java.util.AbstractSequentialList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

import org.apache.commons.lang3.reflect.FieldUtils;
import org.junit.Assert;
import org.junit.Test;

public class FieldUtilsTest {

    @Test
    public void testGetAllFieldsList() {

        // Get all fields in this class and all of its parents
        final List allFields = FieldUtils.getAllFieldsList(LinkedList.class);

        // Get the fields form each individual class in the type's hierarchy
        final List allFieldsClass = Arrays.asList(LinkedList.class.getFields());
        final List allFieldsParent = Arrays.asList(AbstractSequentialList.class.getFields());
        final List allFieldsParentsParent = Arrays.asList(AbstractList.class.getFields());
        final List allFieldsParentsParentsParent = Arrays.asList(AbstractCollection.class.getFields());

        // Test that `getAllFieldsList` did truly get all of the fields of the the class and all its parents 
        Assert.assertTrue(allFields.containsAll(allFieldsClass));
        Assert.assertTrue(allFields.containsAll(allFieldsParent));
        Assert.assertTrue(allFields.containsAll(allFieldsParentsParent));
        Assert.assertTrue(allFields.containsAll(allFieldsParentsParentsParent));
    }
}