Android工作室如何在MainActivity.kt中调用java class？

Question

I am new in android Studio, I have this code in my MainActivity.kt

how do i call java class in my MainActivity.kt ? how do i know if i am connected to my database? my database is postgresql

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        btn_login.setOnClickListener{
            connectionDb()

            Log.i("connectinDb()", "Connected")
        }
    }
}

and i have this java class name connectionDB.java which connect to my postgresql

public class connectionDb {
    Connection connection=null;
    public Connection ConnectionDb(){
        try{
            Class.forName("org.postgresql.Driver");
            connection = DriverManager.getConnection("jdbc:postgresql://localhost:5432/mytransactiondb", "postgres", "root");

        } catch (Exception err) {
            System.err.println(err.getMessage());
        }
        return connection;
    }
    protected void close_connection(Connection con)throws Exception{
        con.close();
    }
}

Thanks in advance.

Answer 1

Modify the code and create an object of Connection class and get methods.

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        btn_login.setOnClickListener{
            //connectionDb()
        val objConnectionDb=connectionDb()
        Log.i("connectinDb()", "Connected")
        }
    }
}