ROOM DATABASE TUTORIAL

Download Full Source Code

1. Create New Android App


2. Update Gradle Files

ext {
roomVersion = '2.2.1'
}

3.Add the following code to the end of the dependencies block:

// Room components
implementation "androidx.room:room-runtime:$rootProject.roomVersion"
annotationProcessor "androidx.room:room-compiler:$rootProject.roomVersion"
androidTestImplementation "androidx.room:room-testing:$rootProject.roomVersion"

4. Create Class Student.class

@Entity

public class Student

{

    @PrimaryKey(autoGenerate = true)

    int ID;

    @NonNull

    @ColumnInfo(name = "name")

    private String name;

    public Student(String name)

    {

        this.name = name;

    }

    public String getName()

    {

        return this.name;

    }

}

5. Create Dao Interface

@Dao

public interface StudentDao {

    // allowing the insert of the same word multiple times by passing a

    // conflict resolution strategy

    @Insert(onConflict = OnConflictStrategy.REPLACE)

    void insert(Student student);

    @Query("DELETE FROM student")

    void deleteAll();

    @Query("SELECT * from student ORDER BY ID ASC")

    List<Student> getAll();

}

6. Create Database Class :

@Database(entities = {Student.class}, version = 3, exportSchema = false)

public abstract class StudentRoomDatabase extends RoomDatabase

{

    public abstract StudentDao studentDao();

    private static volatile StudentRoomDatabase INSTANCE;

    private static final int NUMBER_OF_THREADS = 4;

    static final ExecutorService databaseWriteExecutor =

            Executors.newFixedThreadPool(NUMBER_OF_THREADS);

    static StudentRoomDatabase getDatabase(final Context context)

    {

        if (INSTANCE == null)

        {

            synchronized (StudentRoomDatabase.class)

            {

                if (INSTANCE == null)

                {

                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),

                            StudentRoomDatabase.class, "db")

                            .allowMainThreadQueries()

                            .build();

                }

            }

        }

        return INSTANCE;

    }

}

7. Create MainActivity.java 

public class MainActivity extends AppCompatActivity

{

    EditText et;

    Button btnInsert;

    ListView listView;

    StudentRoomDatabase db;

    @Override

    public void onCreate(@Nullable Bundle savedInstanceState)

    {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        et = findViewById(R.id.etName);

        btnInsert = findViewById(R.id.btnInsert);

        listView = findViewById(R.id.listView);

        db = StudentRoomDatabase.getDatabase(getApplicationContext());

        loadListView();

        btnInsert.setOnClickListener(view ->

        {

            String name = et.getText().toString().trim();

            if (TextUtils.isEmpty(name))

            {

                Toast.makeText(this, "Invalid inputs", Toast.LENGTH_SHORT).show();

                return;

            }

            Student std = new Student(et.getText().toString().trim());

            db.studentDao().insert(std);

            et.setText("");

            loadListView();

        });

    }

    private void loadListView()

    {

        ArrayAdapter adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, db.studentDao().getAll());

        listView.setAdapter(adapter);

    }

}

8. Create Layout File activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical">

    <EditText

        android:layout_width="match_parent"

        android:id="@+id/etName"

        android:hint="Enter Name"

        android:layout_height="wrap_content"></EditText>

    <Button

        android:layout_width="wrap_content"

        android:text="Insert"

        android:id="@+id/btnInsert"

        android:onClick="insert"

        android:layout_height="wrap_content"></Button>

    <ListView

        android:layout_width="match_parent"

        android:id="@+id/listView"

        android:layout_height="wrap_content"></ListView>

</LinearLayout>