哪里错？？

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.DriverManager;

public class login {
private Connection con;
private PreparedStatement pst;
private ResultSet rs;

public login() {
}

public void getCon() {
con = null;
pst = null;
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/user", "root", "490507724");
} catch (Exception e) {
e.printStackTrace();
}
}

public ResultSet getResultSet(String sql) {
rs = null;
getCon();
try {
pst.executeQuery(sql);
} catch (Exception e) {
e.printStackTrace();
}
return rs;
}
}

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.Res