indonesia oop

package Tugas;
import java.util.*;
public class Indonesia {
    public static void main(String[] args) {
        TreeMap<String, TreeMap<String, String>> pulau = new TreeMap();
        TreeMap<String, String> propinsi = new TreeMap();

        pulau.put("Sumatera", new TreeMap<String, String>());
        TreeMap<String, String> sumatera = pulau.get("Sumatera");
        sumatera.put("Nanggro Aceh Darussalam", "Banda Aceh");
        sumatera.put("Sumatera Utara", "Medan");
        sumatera.put("Sumatera Barat", "Padang");
        sumatera.put("Riau", "Pekan Baru");
        sumatera.put("Kepulauan Riau", "Tanjung Pinang");
        sumatera.put("Jambi", "Jambi");
        sumatera.put("Sumatera Selatan", "Palembang");
        sumatera.put("Bangka Belitung", "Pangkal Pinang");
        sumatera.put("Bengkulu", "Bengkulu");
        sumatera.put("Lampung", "Bandar Lampung");
        System.out.println("Ibukota propinsi yang terdapat di Pulau Sumatera\t: \n");
        System.out.println( toStringWrapper(pulau.get("Sumatera")));

        pulau.put("Jawa", new TreeMap<String, String>());
        TreeMap<String, String> jawa = pulau.get("Jawa");
        jawa.put("DKI Jakarta", "Jakarta");
        jawa.put("Jawa Barat", "Bandung");
        jawa.put("Banten", "Serang");
        jawa.put("Jawa Tengah", "Semarang");
        jawa.put("Daerah Istimewa Yogyakarta", "Yogyakarta");
        jawa.put("Jawa Timur", "Surabaya");
        System.out.println(toStringWrapper(pulau.get("Jawa")));
        System.out.println("\nIbukota propinsi yang terdapat di Pulau Jawa\t: \n");
        System.out.println(toStringWrapper(pulau.get("Jawa") ));

        pulau.put("Sulawesi", new TreeMap<String, String>());
        TreeMap<String, String> sulawesi = pulau.get("Sulawesi");

        sulawesi.put("Sulawesi Utara", "Manado");
        sulawesi.put("Sulawesi Barat", "Kota Mamuju");
        sulawesi.put("Sulawesi Tengah", "Palu");
        sulawesi.put("Sulawesi Tenggara", "Kendari");
        sulawesi.put("Sulawesi Selatan", "Makassar");
        sulawesi.put("Gorontalo", "Gorontalo");

        System.out.println("\nIbukota propinsi yang berawalan 'S'\t: ");
        for (TreeMap<String, String> map : pulau.values()) {
            SortedMap<String, String> data = map.tailMap("S");
            System.out.println(data.size() <= 0 ? ("") : toStringWrapper(data));
        }
    }

    public static String toStringWrapper(Object object){
        return (object.toString().replace("{", "\t").replace("}", "").replace(", ", "\n\t").replace("=", " = "));
    }
}