Armazenamento em Banco de Dados

Para ver mais detalhes sobre a persistência em banco de dados:

GOOGLE DEVELOPERS. Salvar dados usando o SQLite. Disponível em: https://developer.android.com/training/data-storage/sqlite?hl=pt-br. Acesso em: 17 ago. 2025.

Exemplos práticos:

Versão 1:

Pessoa.java

import android.os.Parcel;
import android.os.Parcelable;
import androidx.annotation.NonNull;
public class Pessoa implements Parcelable {
    private int id;
    private String nome, telefone;
    public Pessoa(int id, String nome, String telefone) {
        this.id = id;
        this.nome = nome;
        this.telefone = telefone;
    }
    public Pessoa() {
    }
    protected Pessoa(Parcel in) {
        id = in.readInt();
        nome = in.readString();
        telefone = in.readString();
    }
    public static final Creator<Pessoa> CREATOR = new Creator<Pessoa>() {
        @Override
        public Pessoa createFromParcel(Parcel in) {
            return new Pessoa(in);
        }
        @Override
        public Pessoa[] newArray(int size) {
            return new Pessoa[size];
        }
    };
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getNome() {
        return nome;
    }
    public void setNome(String nome) {
        this.nome = nome;
    }
    public String getTelefone() {
        return telefone;
    }
    public void setTelefone(String telefone) {
        this.telefone = telefone;
    }
    @Override
    public String toString() {
        return nome + " - " + telefone;
    }
    @Override
    public int describeContents() {
        return 0;
    }
    @Override
    public void writeToParcel(@NonNull Parcel dest, int flags) {
        dest.writeInt(id);
        dest.writeString(nome);
        dest.writeString(telefone);
    }
}//class

DBHelper.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import androidx.annotation.Nullable;
public class DBHelper extends SQLiteOpenHelper {
    public static final int BANCO_VERSAO = 1;
    public static final String BANCO_NOME = "banco.db";
    public static final String BANCO_TABELA = "Contato";
    public static final String ID = "_id";
    public static final String NOME = "nome";
    public static final String TELEFONE = "telefone";
    private static final String CRIA_TABELA =
            "CREATE TABLE " + BANCO_TABELA +
                    "(" + ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                    NOME + " TEXT, " + TELEFONE + " TEXT" + ")";
    private static final String DELETA_TABELA = "DROP TABLE IF EXISTS " +
            BANCO_TABELA;
    public DBHelper(@Nullable Context context) {
        super(context, BANCO_NOME, null, BANCO_VERSAO);
    }
    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(CRIA_TABELA);
    }
    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
        sqLiteDatabase.execSQL(DELETA_TABELA);
        onCreate(sqLiteDatabase);
    }
}//class

DatabaseManager.java

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
public class DatabaseManager {
    private DBHelper dbHelper;
    private SQLiteDatabase database;
    public DatabaseManager(Context context) {
        dbHelper = new DBHelper(context);
    }
    public void open() {
        database = dbHelper.getWritableDatabase();
    }
    public void close() {
        dbHelper.close();
    }
    public long adicionar(Pessoa p){
        ContentValues values = new ContentValues();
        values.put(DBHelper.NOME, p.getNome());
        values.put(DBHelper.TELEFONE, p.getTelefone());
        return database.insert(DBHelper.BANCO_TABELA,
                null, values);
    }
    public ArrayList<Pessoa> listar(){
        ArrayList<Pessoa> dados = new ArrayList<>();
        String consulta = "SELECT * FROM " + DBHelper.BANCO_TABELA;
        Cursor cursor = database.rawQuery(consulta, null);
        while(cursor.moveToNext()){
            Pessoa p = new Pessoa();
            p.setId(cursor.getInt(0));
            p.setNome(cursor.getString(1));
            p.setTelefone(cursor.getString(2));
            dados.add(p);
        }
        cursor.close();
        return dados;
    }
    public int atualizar(Pessoa p){
        ContentValues values = new ContentValues();
        values.put(DBHelper.NOME, p.getNome());
        values.put(DBHelper.TELEFONE, p.getTelefone());
        String where = DBHelper.ID + "=?";
        String[] args = {String.valueOf(p.getId())};
        return database.update(DBHelper.BANCO_TABELA,
                values, where, args);
    }
    public int excluir(Pessoa p){
        String where = DBHelper.ID + "=?";
        String[] args = {String.valueOf(p.getId())};
        return database.delete(DBHelper.BANCO_TABELA, where, args);
    }
}//class

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context=".MainActivity">
    <EditText
        android:id="@+id/editTextNome"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Digite seu nome" />
    <EditText
        android:id="@+id/editTextTelefone"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Digite seu telefone"
        android:inputType="phone" />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_marginTop="16dp">
        <Button
            android:id="@+id/buttonS"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="SAVE"
            android:onClick="clicar" />
        <Button
            android:id="@+id/buttonL"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="LIST"
            android:onClick="clicar" />
        <Button
            android:id="@+id/buttonD"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="DELETE"
            android:onClick="clicar" />
    </LinearLayout>
</LinearLayout>

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
    private EditText editTextNome, editTextTelefone;
    private Button buttonS, buttonD, buttonL;
    private Pessoa p;
    private DatabaseManager databaseManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editTextNome = findViewById(R.id.editTextNome);
        editTextTelefone = findViewById(R.id.editTextTelefone);
        buttonS = findViewById(R.id.buttonS);
        buttonL = findViewById(R.id.buttonL);
        buttonD = findViewById(R.id.buttonD);
        databaseManager = new DatabaseManager(this);
        databaseManager.open();
        p = getIntent().getParcelableExtra("dado");
        if(p != null){
            editTextNome.setText(p.getNome());
            editTextTelefone.setText(p.getTelefone());
        }
    }
    public void clicar(View view) {
        if (view.getId() == R.id.buttonS ) {
            if (p == null) {
                p = new Pessoa();
                p.setNome(editTextNome.getText().toString());
                p.setTelefone(editTextTelefone.getText().toString());
                long retorno = databaseManager.adicionar(p);
                if (retorno != -1) {
                    Toast.makeText(MainActivity.this, "Salvo",
                            Toast.LENGTH_SHORT).show();
                    p = null;
                    editTextNome.setText("");
                    editTextTelefone.setText("");
                } else {
                    Toast.makeText(MainActivity.this, "Erro ao salvar",
                            Toast.LENGTH_SHORT).show();
                }
            } else {
                p.setNome(editTextNome.getText().toString());
                p.setTelefone(editTextTelefone.getText().toString());
                int retorno = databaseManager.atualizar(p);
                if (retorno != 0) {
                    Toast.makeText(MainActivity.this, "Atualizado",
                            Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(MainActivity.this, "Erro ao atualizar",
                            Toast.LENGTH_SHORT).show();
                }
            }
        }
        if (view.getId() == R.id.buttonL ) {
            ArrayList<Pessoa> dados = databaseManager.listar();
            Log.i("dados", dados.toString());
            if (dados != null && !dados.isEmpty()) {
                Intent it = new Intent(MainActivity.this,
                        SegundaActivity.class);
                it.putParcelableArrayListExtra("dados", dados);
                startActivity(it);
            } else {
                Toast.makeText(MainActivity.this, "Sem dados",
                        Toast.LENGTH_SHORT).show();
            }
        }
        if (view.getId() == R.id.buttonD) {
            if (p != null) {
                int retorno = databaseManager.excluir(p);
                if (retorno > 0) {
                    Toast.makeText(MainActivity.this, "Dados deletados",
                            Toast.LENGTH_SHORT).show();
                    editTextNome.setText("");
                    editTextTelefone.setText("");
                    p = null;
                } else {
                    Toast.makeText(MainActivity.this, "Erro ao deletar",
                            Toast.LENGTH_SHORT).show();
                }
            } else {
                Toast.makeText(MainActivity.this, "Nenhum registro selecionado",
                        Toast.LENGTH_SHORT).show();
            }
        }
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        databaseManager.close();
    }
}//class

activity_segunda.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".SegundaActivity">
    <ListView
        android:id="@+id/lista"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

SegundaActivity.java

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class SegundaActivity extends AppCompatActivity
        implements AdapterView.OnItemClickListener {
    private ListView lista;
    private ArrayAdapter<Pessoa> adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_segunda);
        lista = findViewById(R.id.lista);
        ArrayList<Pessoa> dados = getIntent().getParcelableArrayListExtra("dados");
        Log.i("dados2", String.valueOf(dados));
        if(dados != null && !dados.isEmpty()){
            adapter = new ArrayAdapter<>(this,
                    android.R.layout.simple_list_item_1, dados);
            lista.setAdapter(adapter);
            lista.setOnItemClickListener(this);
        }
    }
    @Override
    public void onItemClick(AdapterView<?> parent, View view,
                            int position, long id) {
        Pessoa p = (Pessoa) parent.getItemAtPosition(position);
        Intent it = new Intent(SegundaActivity.this,
                MainActivity.class);
        it.putExtra("dado", p);
        startActivity(it);
        finish();
    }
}//class

Versão 2:

User.java

public class User {
    private long id;
    private String name;
    private int age;
    public User(long id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public long getId() { return id; }
    public void setId(long id) { this.id = id; }
    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; }
    @Override
    public String toString() {
        return "User{id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age + '}';
    }
}

UserContract.java

import android.provider.BaseColumns;
public class UserContract implements BaseColumns {
    public static final String TABLE_NAME = "user";
    public static final String COLUMN_NAME = "name";
    public static final String COLUMN_AGE = "age";
}

UserDAO.java

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class UserDAO {
    private SQLiteDatabase db;
    public UserDAO(SQLiteDatabase db) {
        this.db = db;
    }
    public long insertUser(String name, int age) {
        if (db != null) {
            ContentValues values = new ContentValues();
            values.put(UserContract.COLUMN_NAME, name);
            values.put(UserContract.COLUMN_AGE, age);
            return db.insert(UserContract.TABLE_NAME, null, values);
        }
        return -1;
    }
    public List<User> getAll() {
        List<User> users = new ArrayList<>();
        if (db != null) {
            String[] columns = {
                    UserContract._ID,
                    UserContract.COLUMN_NAME,
                    UserContract.COLUMN_AGE
            };
            Cursor cursor = db.query(
                    UserContract.TABLE_NAME,
                    columns,
                    null, null, null, null, null
            );
            while (cursor.moveToNext()) {
                long id_user = cursor.getLong(cursor.getColumnIndexOrThrow(UserContract._ID));
                String name_user = cursor.getString(cursor.getColumnIndexOrThrow(UserContract.COLUMN_NAME));
                int age_user = cursor.getInt(cursor.getColumnIndexOrThrow(UserContract.COLUMN_AGE));
                users.add(new User(id_user, name_user, age_user));
            }
            cursor.close();
        }
        return users;
    }
}

DBHelper.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "banco.db";
    private static final int DATABASE_VERSION = 1;
    private static final String SQL_CREATE_TABLE =
            "CREATE TABLE " + UserContract.TABLE_NAME + " (" +
                    UserContract._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                    UserContract.COLUMN_NAME + " TEXT, " +
                    UserContract.COLUMN_AGE + " INTEGER)";
    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_TABLE);
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + UserContract.TABLE_NAME);
        onCreate(db);
    }
}

DBManager.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
public class DBManager {
    private DBHelper dbHelper;
    private SQLiteDatabase database;
    public DBManager(Context context) {
        dbHelper = new DBHelper(context);
    }
    public void open() {
        database = dbHelper.getWritableDatabase();
    }
    public void close() {
        dbHelper.close();
    }
    public SQLiteDatabase getDatabase() {
        return database;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <Button
            android:id="@+id/buttonInsert"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="clicar"
            android:text="Inserir" />
        <Button
            android:id="@+id/buttonList"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="clicar"
            android:text="Listar" />
    </LinearLayout>
    <TextView
        android:id="@+id/textViewResult"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="16dp"
        android:text="resultado" />
</LinearLayout>

MainActivity.java

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.List;
public class MainActivity extends AppCompatActivity {
    private UserDAO userDAO;
    private DBManager databaseManager;
    private Button buttonInsert, buttonList;
    private TextView textViewResult;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        databaseManager = new DBManager(this);
        databaseManager.open();
        userDAO = new UserDAO(databaseManager.getDatabase());
        buttonInsert = findViewById(R.id.buttonInsert);
        buttonList = findViewById(R.id.buttonList);
        textViewResult = findViewById(R.id.textViewResult);
    }
    public void clicar(View view) {
        if (view.getId() == R.id.buttonInsert) {
            long userId1 = userDAO.insertUser("Ana", 30);
            long userId2 = userDAO.insertUser("Rodrigo", 20);
            String result = "Inserted IDs: " + userId1 + " - " + userId2;
            textViewResult.setText(result);
        }
        if (view.getId() == R.id.buttonList) {
            List<User> dados = userDAO.getAll();
            textViewResult.setText(dados.toString());
        }
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        databaseManager.close();
    }
}

Versão 3 (2 entidades e multiplicidade 1:1):

DBHelper.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "escola.db";
    private static final int DATABASE_VERSION = 1;
    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(
                "CREATE TABLE disciplina (" +
                        "id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                        "nome TEXT UNIQUE)"
        );
        db.execSQL(
                "CREATE TABLE aluno (" +
                        "id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                        "nome TEXT UNIQUE, " +
                        "disciplina_id INTEGER UNIQUE, " +
                        "FOREIGN KEY(disciplina_id) REFERENCES disciplina(id) ON DELETE CASCADE)"
        );
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS aluno");
        db.execSQL("DROP TABLE IF EXISTS disciplina");
        onCreate(db);
    }
}

DBManager.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
public class DBManager {
    private DBHelper dbHelper;
    private SQLiteDatabase database;
    public DBManager(Context context) {
        dbHelper = new DBHelper(context);
    }
    public void open() {
        database = dbHelper.getWritableDatabase();
        database.setForeignKeyConstraintsEnabled(true);
    }
    public void close() {
        dbHelper.close();
    }
    public SQLiteDatabase getDatabase() {
        return database;
    }
}

Aluno.java

public class Aluno {
    private long id;
    private String nome;
    private long disciplinaId;
    public Aluno(long id, String nome, long disciplinaId) {
        this.id = id;
        this.nome = nome;
        this.disciplinaId = disciplinaId;
    }
    public long getId() { return id; }
    public String getNome() { return nome; }
    public long getDisciplinaId() { return disciplinaId; }
    @Override
    public String toString() {
        return "Aluno{" +
                "id=" + id +
                ", nome='" + nome + '\'' +
                ", disciplinaId=" + disciplinaId +
                '}';
    }
}

AlunoDAO.java

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class AlunoDAO {
    private SQLiteDatabase db;
    public AlunoDAO(SQLiteDatabase db) {
        this.db = db;
    }
    public long insert(String nome, long disciplinaId) {
        ContentValues values = new ContentValues();
        values.put("nome", nome);
        values.put("disciplina_id", disciplinaId);
        return db.insert("aluno", null, values);
    }
    public List<Aluno> getAll() {
        List<Aluno> list = new ArrayList<>();
        Cursor cursor = db.query("aluno", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            long id = cursor.getLong(cursor.getColumnIndexOrThrow("id"));
            String nome = cursor.getString(cursor.getColumnIndexOrThrow("nome"));
            long disciplinaId = cursor.getLong(cursor.getColumnIndexOrThrow("disciplina_id"));
            list.add(new Aluno(id, nome, disciplinaId));
        }
        cursor.close();
        return list;
    }
}

Disciplina.java

public class Disciplina {
    private long id;
    private String nome;
    public Disciplina(long id, String nome) {
        this.id = id;
        this.nome = nome;
    }
    public long getId() { return id; }
    public String getNome() { return nome; }
    @Override
    public String toString() {
        return "Disciplina{" +
                "id=" + id +
                ", nome='" + nome + '\'' +
                '}';
    }
}

DisciplinaDAO.java

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class DisciplinaDAO {
    private SQLiteDatabase db;
    public DisciplinaDAO(SQLiteDatabase db) {
        this.db = db;
    }
    public long insert(String nome) {
        ContentValues values = new ContentValues();
        values.put("nome", nome);
        return db.insert("disciplina", null, values);
    }
    public List<Disciplina> getAll() {
        List<Disciplina> list = new ArrayList<>();
        Cursor cursor = db.query("disciplina", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            long id = cursor.getLong(cursor.getColumnIndexOrThrow("id"));
            String nome = cursor.getString(cursor.getColumnIndexOrThrow("nome"));
            list.add(new Disciplina(id, nome));
        }
        cursor.close();
        return list;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <Button
            android:id="@+id/buttonInserir"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="clicar"
            android:text="Inserir" />
        <Button
            android:id="@+id/buttonListar"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="clicar"
            android:text="Listar" />
    </LinearLayout>
    <TextView
        android:id="@+id/textViewResult"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="resultado" />
</LinearLayout>

MainActivity.java

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.List;
public class MainActivity extends AppCompatActivity {
    private DBManager dbManager;
    private AlunoDAO alunoDAO;
    private DisciplinaDAO disciplinaDAO;
    private Button btnInsert, btnList;
    private TextView textViewResult;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbManager = new DBManager(this);
        dbManager.open();
        alunoDAO = new AlunoDAO(dbManager.getDatabase());
        disciplinaDAO = new DisciplinaDAO(dbManager.getDatabase());
        btnInsert = findViewById(R.id.buttonInserir);
        btnList = findViewById(R.id.buttonListar);
        textViewResult = findViewById(R.id.textViewResult);
    }
    public void clicar(View view) {
        if (view.getId() == R.id.buttonInserir) {
            long mat1 = disciplinaDAO.insert("Matemática");
            long hist1 = disciplinaDAO.insert("História");
            long aluno1 = alunoDAO.insert("Ana", mat1);
            long aluno2 = alunoDAO.insert("João", hist1);
            long aluno3 = alunoDAO.insert("João", mat1);
            textViewResult.setText("Mat=" + mat1 + " Hist=" + hist1 +
                    "\nAluno1=" + aluno1 +
                    "\nAluno2=" + aluno2 +
                    "\nAluno3=" + aluno3);
        }
        if (view.getId() == R.id.buttonListar) {
            List<Aluno> alunos = alunoDAO.getAll();
            List<Disciplina> disciplinas = disciplinaDAO.getAll();
            textViewResult.setText("Alunos: " + alunos + "\nDisciplinas: " + disciplinas);
        }
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        dbManager.close();
    }
}

Versão 4 (2 entidades e multiplicidade N:N):

DatabaseContract.java

import android.provider.BaseColumns;
public final class DatabaseContract {
    private DatabaseContract() {}
    public static class AlunoEntry implements BaseColumns {
        public static final String TABLE_NAME = "aluno";
        public static final String COLUMN_NOME = "nome";
        public static final String COLUMN_IDADE = "idade";
    }
    public static class DisciplinaEntry implements BaseColumns {
        public static final String TABLE_NAME = "disciplina";
        public static final String COLUMN_NOME = "nome";
    }
    public static class AlunoDisciplinaEntry implements BaseColumns {
        public static final String TABLE_NAME = "aluno_disciplina";
        public static final String COLUMN_ALUNO_ID = "aluno_id";
        public static final String COLUMN_DISCIPLINA_ID = "disciplina_id";
    }
}

DBHelper.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "escola.db";
    private static final int DATABASE_VERSION = 1;
    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(
                "CREATE TABLE " + DatabaseContract.AlunoEntry.TABLE_NAME + " (" +
                        DatabaseContract.AlunoEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
                        DatabaseContract.AlunoEntry.COLUMN_NOME + " TEXT UNIQUE," +
                        DatabaseContract.AlunoEntry.COLUMN_IDADE + " INTEGER)"
        );
        db.execSQL(
                "CREATE TABLE " + DatabaseContract.DisciplinaEntry.TABLE_NAME + " (" +
                        DatabaseContract.DisciplinaEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
                        DatabaseContract.DisciplinaEntry.COLUMN_NOME + " TEXT UNIQUE)"
        );
        db.execSQL(
                "CREATE TABLE " + DatabaseContract.AlunoDisciplinaEntry.TABLE_NAME + " (" +
                        DatabaseContract.AlunoDisciplinaEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
                        DatabaseContract.AlunoDisciplinaEntry.COLUMN_ALUNO_ID + " INTEGER," +
                        DatabaseContract.AlunoDisciplinaEntry.COLUMN_DISCIPLINA_ID + " INTEGER," +
                        "UNIQUE(" + DatabaseContract.AlunoDisciplinaEntry.COLUMN_ALUNO_ID + "," +
                        DatabaseContract.AlunoDisciplinaEntry.COLUMN_DISCIPLINA_ID + ")," +
                        "FOREIGN KEY(" + DatabaseContract.AlunoDisciplinaEntry.COLUMN_ALUNO_ID + ") REFERENCES " +
                        DatabaseContract.AlunoEntry.TABLE_NAME + "(" + DatabaseContract.AlunoEntry._ID + ") ON DELETE CASCADE," +
                        "FOREIGN KEY(" + DatabaseContract.AlunoDisciplinaEntry.COLUMN_DISCIPLINA_ID + ") REFERENCES " +
                        DatabaseContract.DisciplinaEntry.TABLE_NAME + "(" + DatabaseContract.DisciplinaEntry._ID + ") ON DELETE CASCADE)"
        );
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + DatabaseContract.AlunoDisciplinaEntry.TABLE_NAME);
        db.execSQL("DROP TABLE IF EXISTS " + DatabaseContract.AlunoEntry.TABLE_NAME);
        db.execSQL("DROP TABLE IF EXISTS " + DatabaseContract.DisciplinaEntry.TABLE_NAME);
        onCreate(db);
    }
}

DBManager.java

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
public class DBManager {
    private DBHelper dbHelper;
    private SQLiteDatabase database;
    public DBManager(Context context) {
        dbHelper = new DBHelper(context);
    }
    public void open() {
        database = dbHelper.getWritableDatabase();
        database.setForeignKeyConstraintsEnabled(true);
    }
    public void close() {
        dbHelper.close();
    }
    public SQLiteDatabase getDatabase() {
        return database;
    }
}

Aluno.java

public class Aluno {
    private long id;
    private String nome;
    private int idade;
    public Aluno(long id, String nome, int idade) {
        this.id = id;
        this.nome = nome;
        this.idade = idade;
    }
    public long getId() { return id; }
    public String getNome() { return nome; }
    public int getIdade() { return idade; }
    @Override
    public String toString() {
        return "Aluno{" + "id=" + id + ", nome='" + nome + '\'' + ", idade=" + idade + '}';
    }
}

AlunoDAO.java

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class AlunoDAO {
    private SQLiteDatabase db;
    public AlunoDAO(SQLiteDatabase db) {
        this.db = db;
    }
    public long insert(String nome, int idade) {
        ContentValues values = new ContentValues();
        values.put("nome", nome);
        values.put("idade", idade);
        return db.insert("aluno", null, values);
    }
    public List<Aluno> getAll() {
        List<Aluno> list = new ArrayList<>();
        Cursor cursor = db.query("aluno", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            long id = cursor.getLong(cursor.getColumnIndexOrThrow("id"));
            String nome = cursor.getString(cursor.getColumnIndexOrThrow("nome"));
            int idade = cursor.getInt(cursor.getColumnIndexOrThrow("idade"));
            list.add(new Aluno(id, nome, idade));
        }
        cursor.close();
        return list;
    }
}

Disciplina.java

public class Disciplina {
    private long id;
    private String nome;
    public Disciplina(long id, String nome) {
        this.id = id;
        this.nome = nome;
    }
    public long getId() { return id; }
    public String getNome() { return nome; }
    @Override
    public String toString() {
        return "Disciplina{" + "id=" + id + ", nome='" + nome + '\'' + '}';
    }
}

DisciplinaDAO.java

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class DisciplinaDAO {
    private SQLiteDatabase db;
    public DisciplinaDAO(SQLiteDatabase db) {
        this.db = db;
    }
    public long insert(String nome) {
        ContentValues values = new ContentValues();
        values.put("nome", nome);
        return db.insert("disciplina", null, values);
    }
    public List<Disciplina> getAll() {
        List<Disciplina> list = new ArrayList<>();
        Cursor cursor = db.query("disciplina", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            long id = cursor.getLong(cursor.getColumnIndexOrThrow("id"));
            String nome = cursor.getString(cursor.getColumnIndexOrThrow("nome"));
            list.add(new Disciplina(id, nome));
        }
        cursor.close();
        return list;
    }
}

AlunoDisciplinaDAO.java

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class AlunoDisciplinaDAO {
    private SQLiteDatabase db;
    public AlunoDisciplinaDAO(SQLiteDatabase db) {
        this.db = db;
    }
    public long linkAlunoDisciplina(long alunoId, long disciplinaId) {
        ContentValues values = new ContentValues();
        values.put("aluno_id", alunoId);
        values.put("disciplina_id", disciplinaId);
        return db.insert("aluno_disciplina", null, values);
    }
    public List<String> getAlunosDisciplinas() {
        List<String> list = new ArrayList<>();
        Cursor cursor = db.rawQuery(
                "SELECT a.nome, d.nome FROM aluno_disciplina ad " +
                        "JOIN aluno a ON a.id = ad.aluno_id " +
                        "JOIN disciplina d ON d.id = ad.disciplina_id", null
        );
        while (cursor.moveToNext()) {
            String aluno = cursor.getString(0);
            String disciplina = cursor.getString(1);
            list.add(aluno + " -> " + disciplina);
        }
        cursor.close();
        return list;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <Button
            android:id="@+id/buttonInserir"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="clicar"
            android:text="Inserir" />
        <Button
            android:id="@+id/buttonListar"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="clicar"
            android:text="Listar" />
    </LinearLayout>
    <TextView
        android:id="@+id/textViewResult"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="resultado" />
</LinearLayout>

MainActivity.java

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
import java.util.List;
public class MainActivity extends AppCompatActivity {
    private DBManager dbManager;
    private AlunoDAO alunoDAO;
    private DisciplinaDAO disciplinaDAO;
    private AlunoDisciplinaDAO alunoDisciplinaDAO;
    private Button btnInserir, btnListar;
    private TextView textViewResult;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbManager = new DBManager(this);
        dbManager.open();
        alunoDAO = new AlunoDAO(dbManager.getDatabase());
        disciplinaDAO = new DisciplinaDAO(dbManager.getDatabase());
        alunoDisciplinaDAO = new AlunoDisciplinaDAO(dbManager.getDatabase());
        btnInserir = findViewById(R.id.buttonInserir);
        btnListar = findViewById(R.id.buttonListar);
        textViewResult = findViewById(R.id.textViewResult);
    }
    public void clicar(View view) {
        if (view.getId() == R.id.buttonInserir) {
            long aluno1 = alunoDAO.insert("Ana", 20);
            long aluno2 = alunoDAO.insert("João", 22);
            long disc1 = disciplinaDAO.insert("Matemática");
            long disc2 = disciplinaDAO.insert("História");
            alunoDisciplinaDAO.linkAlunoDisciplina(aluno1, disc1);
            alunoDisciplinaDAO.linkAlunoDisciplina(aluno1, disc2);
            alunoDisciplinaDAO.linkAlunoDisciplina(aluno2, disc1);
            textViewResult.setText("Inserido com sucesso!");
        }
        if (view.getId() == R.id.buttonListar) {
            List<String> list = alunoDisciplinaDAO.getAlunosDisciplinas();
            StringBuilder sb = new StringBuilder();
            for (String s : list) sb.append(s).append("\n");
            textViewResult.setText(sb.toString());
        }
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        dbManager.close();
    }
}

Para visualizar as tabelas criadas no aplicativo é necessário exportar o arquivo .db e usar um aplicativo específico, por exemplo o SQLiteStudio, disponível em: https://sqlitestudio.pl/.

Armazenamento em Banco de Dados - SQLite