如何创建一个新的类的方法?

什么你需要的是改变你 Hotel 类别的东西。 实际上，你需要的一类有一个构造接受 nama, jenis 和 lama. 在这你的计算 kamar 和 tarif 如下(我把它叫做 HotelReservation 因为这似乎是更适当的话):

public class HotelReservation {
    private final String nama;
    private final String kamar;
    private final int tarif;

    public HotelReservation(String nama, String jenis, int lama){
        this.nama = nama;

        switch (jenis) {
            case "R":
                tarif = lama * 300000;
                kamar = "Reguler";
                break;
            case "S":
                tarif = lama * 500000;
                kamar = "Suite";
                break;
            case "P":
                tarif = lama * 750000;
                kamar = "President";
                break;
            default:
                tarif = 0;
                kamar = "Invalid";
                break;
        }
    }

    public String getNama() {
        return nama;
    }

    public String getKamar() {
        return kamar;
    }

    public int getTarif() {
        return tarif;
    }
}

与这个类，现在，您可以创建一个新酒店预订在你的主要方法中给出的数据用户：

public class Main {
    public static void main (String [] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        System.out.println("--**-- SISTEM INFORMASI PERHOTELAN --**--");
        System.out.print("Nama Pelanggan \t\t\t: ");
        String nama = br.readLine();

        System.out.println("\nPilih Jenis Kamar");
        System.out.println("R. Reguler");
        System.out.println("S. Suite");
        System.out.println("P. President");
        System.out.print("Jenis kamar yang dipesan (R/S/P) \t: ");
        String jenis = br.readLine();

        System.out.print("\nLama Menginap \t\t\t: ");
        int lama = Integer.parseInt(br.readLine());

        HotelReservation hotelReservation = new HotelReservation(nama, jenis, lama);

        System.out.println("\n\n---***--- NOTA PEMBAYARAN HOTEL ---***---");
        System.out.println("Nama Pelanggan \t\t\t: " + hotelReservation.getNama());
        System.out.println("Jenis Kamar \t\t\t: " + hotelReservation.getKamar());
        System.out.println("Tarif Penginapan \t\t: Rp " + hotelReservation.getTarif() + ",-");
        System.out.println("====================================================");
    }
}