Java

public class Dog extends RealmObject {
    public String name;
    public int age;
}

Dog dog = new Dog();
dog.name = "Rex";
dog.age = 1;

Realm realm = Realm.getDefaultInstance();
realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        realm.copyToRealmOrUpdate(dog);
    }
});

RealmResults<Dog> pups = realm.where(Dog.class)
                               .lessThan("age", 2)
                               .findAll();