Si ti ringrazio ma ho risolto già, in questo modo:

codice:
package exampleconnectdatabase;

import java.sql.*;
import java.sql.ResultSet;
import javax.sql.DataSource;
import oracle.jdbc.*;
import oracle.jdbc.pool.OracleDataSource;

public class ExampleConnectDatabase {
    
    public static void main(String[] args) {
    
        Connection conn = null;
        String username;

        try {
            OracleDataSource ds = new OracleDataSource();
            ds.setDriverType("thin");
            ds.setServerName("xxx");
            ds.setPortNumber(xxx);
            ds.setDatabaseName("xxxx");
            ds.setUser("xxx");
            ds.setPassword("xxx");
            conn = ds.getConnection();
            Statement statement = conn.createStatement();
            ResultSet rset = statement.executeQuery("select * from ADMIN");
            while (rset.next()) {
                username = rset.getString(2);
                System.out.println("Username: " + username);
            }
            statement.close();
        }
        catch( Exception exception ) {
            System.out.println("Errore script");
        }
        finally {
            if ( conn != null )
            {
                try {
                    conn.close();
                }
                catch( SQLException sqlException ){}
            }
        }    
   }
}
sbagliavo in ResultSet perchè cercavo di richiamare un metodo con il nome execute ma in realtà si chiama executeQuery. Grazie comunque