Minimal Realm

build.gradle (app)

apply plugin: 'com.android.application'
apply plugin: 'realm-android'

android {
    //...
}

dependencies {
    //...
}

build.gradle (project)

buildscript {
    repositories {
        //...
    }
    dependencies {
        //...
        classpath "io.realm:realm-gradle-plugin:2.3.1"
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivityTAG_";

    private Realm realm;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Realm.init(getApplicationContext());
        realm = Realm.getDefaultInstance();

        clearValues();
        insertValues();
        readValues();
    }

    private void clearValues() {
        realm.beginTransaction();
        realm.deleteAll();
        realm.commitTransaction();
    }

    private void insertValues() {
        realm.beginTransaction();

        realm.copyToRealm(new User("Juan", 20));
        realm.copyToRealm(new User("Miguel", 23));
        realm.copyToRealm(new User("Roberto", 39));
        realm.copyToRealm(new User("Luis", 19));
        realm.copyToRealm(new User("Gaudencio", 25));

        realm.commitTransaction();
    }

    private void readValues() {
        List<User> users = realm.where(User.class).findAll();

        for (User user : users) {
            Log.d(TAG, "readValues: " + user);
        }
    }
}

User.java

public class User extends RealmObject {
    private String name;
    private int age;

    public User() {

    }

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}