FooDAO.java

public class FooDAO implements Closeable {
  
  private final Realm realm = Realm.getDefaultInstance();
  
  @Override
  public void close() {
    realm.close();
  }
  
  public void setFooValue(RealmFoo foo, String value) {
    realm.beginTransaction();
    foo.setTrivialValue(value);
    realm.commitTransaction();
  }

RealmFoo.java

public class RealmFoo extends RealmObject {
  
  private String trivialValue;
  
  public String getTrivialValue() {
    return trivialValue;
  }
  
  public void setTrivialValue(String value) {
    trivialValue = value;
  }
}