系统研究Java--容器（二）--使用Abstract类

这个示例在于演示通过继承java.util.Abstract来创建定制的Map和Collection，实现一个只读的Map。

//: net/mindview/util/Countries.java
// "Flyweight" Maps and Lists of sample data.
package net.mindview.util;
import java.util.*;
import static net.mindview.util.Print.*;
public class Countries {
  public static final String[][] DATA = {
    // Africa
    {"ALGERIA","Algiers"}, {"ANGOLA","Luanda"},
    {"BENIN","Porto-Novo"}, {"BOTSWANA","Gaberone"},
    {"BURKINA FASO","Ouagadougou"},
    {"BURUNDI","Bujumbura"},
    {"CAMEROON","Yaounde"}, {"CAPE VERDE","Praia"},
    {"CENTRAL AFRICAN REPUBLIC","Bangui"},
    {"CHAD","N'djamena"},  {"COMOROS","Moroni"},
    {"CONGO","Brazzaville"}, {"DJIBOUTI","Dijibouti"},
    {"EGYPT","Cairo"}, {"EQUATORIAL GUINEA","Malabo"},
    {"ERITREA","Asmara"}, {"ETHIOPIA","Addis Ababa"},
    {"GABON","Libreville"}, {"THE GAMBIA","Banjul"},
    {"GHANA","Accra"}, {"GUINEA","Conakry"},
    {"BISSAU","Bissau"},
    {"COTE D'IVOIR (IVORY COAST)","Yamoussoukro"},
    {"KENYA","Nairobi"}, {"LESOTHO","Maseru"},
    {"LIBERIA","Monrovia"}, {"LIBYA","Tripoli"},
    {"MADAGASCAR","Antananarivo"}, {"MALAWI","Lilongwe"},
    {"MALI","Bamako"}, {"MAURITANIA","Nouakchott"},
    {"MAURITIUS","Port Louis"}, {"MOROCCO","Rabat"},
    {"MOZAMBIQUE","Maputo"}, {"NAMIBIA","Windhoek"},
    {"NIGER","Niamey"}, {"NIGERIA","Abuja"},
    {"RWANDA","Kigali"},
    {"SAO TOME E PRINCIPE","Sao Tome"},
    {"SENEGAL","Dakar"}, {"SEYCHELLES","Victoria"},
    {"SIERRA LEONE","Freetown"}, {"SOMALIA","Mogadishu"},
    {"SOUTH AFRICA","Pretoria/Cape Town"},
    {"SUDAN","Khartoum"},
    {"SWAZILAND","Mbabane"}, {"TANZANIA","Dodoma"},
    {"TOGO","Lome"}, {"TUNISIA","Tunis"},
    {"UGANDA","Kampala"},
    {"DEMOCRATIC REPUBLIC OF THE CONGO (ZAIRE)",
     "Kinshasa"},
    {"ZAMBIA","Lusaka"}, {"ZIMBABWE","Harare"},
    // Asia
    {"AFGHANISTAN","Kabul"}, {"BAHRAIN","Manama"},
    {"BANGLADESH","Dhaka"}, {"BHUTAN","Thimphu"},
    {"BRUNEI","Bandar Seri Begawan"},
    {"CAMBODIA","Phnom Penh"},
    {"CHINA","Beijing"}, {"CYPRUS","Nicosia"},
    {"INDIA","New Delhi"}, {"INDONESIA","Jakarta"},
    {"IRAN","Tehran"}, {"IRAQ","Baghdad"},
    {"ISRAEL","Jerusalem"}, {"JAPAN","Tokyo"},
    {"JORDAN","Amman"}, {"KUWAIT","Kuwait City"},
    {"LAOS","Vientiane"}, {"LEBANON","Beirut"},
    {"MALAYSIA","Kuala Lumpur"}, {"THE MALDIVES","Male"},
    {"MONGOLIA","Ulan Bator"},
    {"MYANMAR (BURMA)","Rangoon"},
    {"NEPAL","Katmandu"}, {"NORTH KOREA","P'yongyang"},
    {"OMAN","Muscat"}, {"PAKISTAN","Islamabad"},
    {"PHILIPPINES","Manila"}, {"QATAR","Doha"},
    {"SAUDI ARABIA","Riyadh"}, {"SINGAPORE","Singapore"},
    {"SOUTH KOREA","Seoul"}, {"SRI LANKA","Colombo"},
    {"SYRIA","Damascus"},
    {"TAIWAN (REPUBLIC OF CHINA)","Taipei"},
    {"THAILAND","Bangkok"}, {"TURKEY","Ankara"},
    {"UNITED ARAB EMIRATES","Abu Dhabi"},
    {"VIETNAM","Hanoi"}, {"YEMEN","Sana'a"},
    // Australia and Oceania
    {"AUSTRALIA","Canberra"}, {"FIJI","Suva"},
    {"KIRIBATI","Bairiki"},
    {"MARSHALL ISLANDS","Dalap-Uliga-Darrit"},
    {"MICRONESIA","Palikir"}, {"NAURU","Yaren"},
    {"NEW ZEALAND","Wellington"}, {"PALAU","Koror"},
    {"PAPUA NEW GUINEA","Port Moresby"},
    {"SOLOMON ISLANDS","Honaira"}, {"TONGA","Nuku'alofa"},
    {"TUVALU","Fongafale"}, {"VANUATU","< Port-Vila"},
    {"WESTERN SAMOA","Apia"},
    // Eastern Europe and former USSR
    {"ARMENIA","Yerevan"}, {"AZERBAIJAN","Baku"},
    {"BELARUS (BYELORUSSIA)","Minsk"},
    {"BULGARIA","Sofia"}, {"GEORGIA","Tbilisi"},
    {"KAZAKSTAN","Almaty"}, {"KYRGYZSTAN","Alma-Ata"},
    {"MOLDOVA","Chisinau"}, {"RUSSIA","Moscow"},
    {"TAJIKISTAN","Dushanbe"}, {"TURKMENISTAN","Ashkabad"},
    {"UKRAINE","Kyiv"}, {"UZBEKISTAN","Tashkent"},
    // Europe
    {"ALBANIA","Tirana"}, {"ANDORRA","Andorra la Vella"},
    {"AUSTRIA","Vienna"}, {"BELGIUM","Brussels"},
    {"BOSNIA","-"}, {"HERZEGOVINA","Sarajevo"},
    {"CROATIA","Zagreb"}, {"CZECH REPUBLIC","Prague"},
    {"DENMARK","Copenhagen"}, {"ESTONIA","Tallinn"},
    {"FINLAND","Helsinki"}, {"FRANCE","Paris"},
    {"GERMANY","Berlin"}, {"GREECE","Athens"},
    {"HUNGARY","Budapest"}, {"ICELAND","Reykjavik"},
    {"IRELAND","Dublin"}, {"ITALY","Rome"},
    {"LATVIA","Riga"}, {"LIECHTENSTEIN","Vaduz"},
    {"LITHUANIA","Vilnius"}, {"LUXEMBOURG","Luxembourg"},
    {"MACEDONIA","Skopje"}, {"MALTA","Valletta"},
    {"MONACO","Monaco"}, {"MONTENEGRO","Podgorica"},
    {"THE NETHERLANDS","Amsterdam"}, {"NORWAY","Oslo"},
    {"POLAND","Warsaw"}, {"PORTUGAL","Lisbon"},
    {"ROMANIA","Bucharest"}, {"SAN MARINO","San Marino"},
    {"SERBIA","Belgrade"}, {"SLOVAKIA","Bratislava"},
    {"SLOVENIA","Ljuijana"}, {"SPAIN","Madrid"},
    {"SWEDEN","Stockholm"}, {"SWITZERLAND","Berne"},
    {"UNITED KINGDOM","London"}, {"VATICAN CITY","---"},
    // North and Central America
    {"ANTIGUA AND BARBUDA","Saint John's"},
    {"BAHAMAS","Nassau"},
    {"BARBADOS","Bridgetown"}, {"BELIZE","Belmopan"},
    {"CANADA","Ottawa"}, {"COSTA RICA","San Jose"},
    {"CUBA","Havana"}, {"DOMINICA","Roseau"},
    {"DOMINICAN REPUBLIC","Santo Domingo"},
    {"EL SALVADOR","San Salvador"},
    {"GRENADA","Saint George's"},
    {"GUATEMALA","Guatemala City"},
    {"HAITI","Port-au-Prince"},
    {"HONDURAS","Tegucigalpa"}, {"JAMAICA","Kingston"},
    {"MEXICO","Mexico City"}, {"NICARAGUA","Managua"},
    {"PANAMA","Panama City"}, {"ST. KITTS","-"},
    {"NEVIS","Basseterre"}, {"ST. LUCIA","Castries"},
    {"ST. VINCENT AND THE GRENADINES","Kingstown"},
    {"UNITED STATES OF AMERICA","Washington, D.C."},
    // South America
    {"ARGENTINA","Buenos Aires"},
    {"BOLIVIA","Sucre (legal)/La Paz(administrative)"},
    {"BRAZIL","Brasilia"}, {"CHILE","Santiago"},
    {"COLOMBIA","Bogota"}, {"ECUADOR","Quito"},
    {"GUYANA","Georgetown"}, {"PARAGUAY","Asuncion"},
    {"PERU","Lima"}, {"SURINAME","Paramaribo"},
    {"TRINIDAD AND TOBAGO","Port of Spain"},
    {"URUGUAY","Montevideo"}, {"VENEZUELA","Caracas"},
  };
  // Use AbstractMap by implementing entrySet()
  private static class FlyweightMap
  extends AbstractMap<String,String> {
    private static class Entry
    implements Map.Entry<String,String> {
      int index;
      Entry(int index) { this.index = index; }
      public boolean equals(Object o) {
        return DATA[index][0].equals(o);
      }
      public String getKey() { return DATA[index][0]; }
      public String getValue() { return DATA[index][1]; }
      public String setValue(String value) {
        throw new UnsupportedOperationException();
      }
      public int hashCode() {
        return DATA[index][0].hashCode();
      }
    }
    // Use AbstractSet by implementing size() & iterator()
    static class EntrySet
    extends AbstractSet<Map.Entry<String,String>> {
      private int size;
      EntrySet(int size) {
        if(size < 0)
          this.size = 0;
        // Can't be any bigger than the array:
        else if(size > DATA.length)
          this.size = DATA.length;
        else
          this.size = size;
      }
      public int size() { return size; }
      private class Iter
      implements Iterator<Map.Entry<String,String>> {
        // Only one Entry object per Iterator:
        private Entry entry = new Entry(-1);
        public boolean hasNext() {
          return entry.index < size - 1;
        }
        public Map.Entry<String,String> next() {
          entry.index++;
          return entry;
        }
        public void remove() {
          throw new UnsupportedOperationException();
        }
      }
      public
      Iterator<Map.Entry<String,String>> iterator() {
        return new Iter();
      }
    }
    private static Set<Map.Entry<String,String>> entries =
      new EntrySet(DATA.length);
    public Set<Map.Entry<String,String>> entrySet() {
      return entries;
    }
  }
  // Create a partial map of 'size' countries:
  static Map<String,String> select(final int size) {
    return new FlyweightMap() {
      public Set<Map.Entry<String,String>> entrySet() {
        return new EntrySet(size);
      }
    };
  }
  static Map<String,String> map = new FlyweightMap();
  public static Map<String,String> capitals() {
    return map; // The entire map
  }
  public static Map<String,String> capitals(int size) {
    return select(size); // A partial map
  }
  static List<String> names =
    new ArrayList<String>(map.keySet());
  // All the names:
  public static List<String> names() { return names; }
  // A partial list:
  public static List<String> names(int size) {
    return new ArrayList<String>(select(size).keySet());
  }
  public static void main(String[] args) {
    print(capitals(10));
    print(names(10));
    print(new HashMap<String,String>(capitals(3)));
    print(new LinkedHashMap<String,String>(capitals(3)));
    print(new TreeMap<String,String>(capitals(3)));
    print(new Hashtable<String,String>(capitals(3)));
    print(new HashSet<String>(names(6)));
    print(new LinkedHashSet<String>(names(6)));
    print(new TreeSet<String>(names(6)));
    print(new ArrayList<String>(names(6)));
    print(new LinkedList<String>(names(6)));
    print(capitals().get("BRAZIL"));
  }
} /* Output:
{ALGERIA=Algiers, ANGOLA=Luanda, BENIN=Porto-Novo, BOTSWANA=Gaberone, BULGARIA=Sofia, BURKINA FASO=Ouagadougou, BURUNDI=Bujumbura, CAMEROON=Yaounde, CAPE VERDE=Praia, CENTRAL AFRICAN REPUBLIC=Bangui}
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BULGARIA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC]
{BENIN=Porto-Novo, ANGOLA=Luanda, ALGERIA=Algiers}
{ALGERIA=Algiers, ANGOLA=Luanda, BENIN=Porto-Novo}
{ALGERIA=Algiers, ANGOLA=Luanda, BENIN=Porto-Novo}
{ALGERIA=Algiers, ANGOLA=Luanda, BENIN=Porto-Novo}
[BULGARIA, BURKINA FASO, BOTSWANA, BENIN, ANGOLA, ALGERIA]
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BULGARIA, BURKINA FASO]
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BULGARIA, BURKINA FASO]
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BULGARIA, BURKINA FASO]
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BULGARIA, BURKINA FASO]
Brasilia
*///:~

源码源于《Thinking in Java》