Android Studio – Can't connect Android application to local PostgreSQL database

I have created a PostgreSQL database schema and I want to connect an android application with the database. I get this error:

"W/System.err: org.postgresql.util.PSQLException: Connection to localhost:5432 refused. Check that the hostname and port are correct and that the postmaster is accepting TCP/IP connections."

Here is my code:

public class Database {

    private Connection connection;

    private final String host = "localhost";
    private final String database = "postgres";
    private final int port = 5432;
    private final String user = "postgres";
    private final String pass = "password";
    private String url = "jdbc:postgresql://%s:%d/%s";
    private boolean status;

    public Database() {
        this.url = String.format(this.url, this.host, this.port, this.database);
        connect();
        //this.disconnect();
        System.out.println("connection status:" + status);
    }

    private void connect() {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Class.forName("org.postgresql.Driver");
                    connection = DriverManager.getConnection(url, user, pass);
                    status = true;
                    System.out.println("connected:" + status);
                } catch (Exception e) {
                    status = false;
                    System.out.print(e.getMessage());
                    e.printStackTrace();
                }
            }
        });
        thread.start();
        try {
            thread.join();
        } catch (Exception e) {
            e.printStackTrace();
            this.status = false;
        }
    }

    public Connection getExtraConnection(){
        Connection c = null;
        try {
            Class.forName("org.postgresql.Driver");
            c = DriverManager.getConnection(url, user, pass);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return c;
    }
}

public class MainActivity extends AppCompatActivity {

    private ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Database db = new Database();
    }
}

When I run netstat -a, it’s all ok, it accepts TCP connections. I can not find anywhere anything that helps for connecting an Android application with a local PostgreSQL database. What is the problem and how can I fix this?