import java.util.AbstractMap;

 import java.util.AbstractSet;

 import java.util.ArrayList;

 import java.util.HashMap;

 import java.util.HashSet;

 import java.util.Hashtable;

 import java.util.Iterator;

 import java.util.LinkedHashMap;

 import java.util.LinkedHashSet;

 import java.util.LinkedList;

 import java.util.List;

 import java.util.Map;

 import java.util.Set;

 import java.util.TreeMap;

 import java.util.TreeSet;

 class Countries {

     public static final String[][] DATA = {

             // Africa

             { "SOUTH AFRICA", "Cape Town" }, { "SUDAN", "Khartoum" },

             // Asia

             { "CHINA", "Beijing" }, { "JAPAN", "Tokyo" }, { "SOUTH KOREA", "Seoul" },

             // Australia and Oceania

             { "AUSTRALIA", "Canberra" }, { "NEW ZEALAND", "Wellington" },

             // Europe

             { "UNITED KINGDOM", "London" }, { "FRANCE", "Paris" }, { "GERMANY", "Berlin" }, { "ITALY", "Rome" },

             { "SPAIN", "Madrid" },

             // North and Central America

             { "UNITED STATES OF AMERICA", "Washington, D.C." }, { "CANADA", "Ottawa" },

             // South America

             { "BRAZIL", "Brasilia" }, { "ARGENTINA", "Buenos Aires" } };

     private static class FlyweightMap extends AbstractMap<String, String> {

         private final int dataLength;

         private static Set<Map.Entry<String, String>> entries = new EntrySet(DATA.length);

         public FlyweightMap() {

             dataLength = 0;

         }

         public FlyweightMap(int dataLength) {

             this.dataLength = dataLength;

         }

         @Override

         public Set<Map.Entry<String, String>> entrySet() {

             if (dataLength > 0) {

                 return new EntrySet(dataLength);

             }

             return entries;

         }

         // (1) 实现Set<E>接口

         // 定制自己的Set实现AbstractSet(AbstractCollection)-->Set， 需要实现[Iterator<E> iterator() & int size()]方法

         private static class EntrySet extends AbstractSet<Map.Entry<String, String>> {

             private int size;

             EntrySet(int size) {

                 this.size = size < 0 ? (this.size = 0)

                         : (size > DATA.length ? (this.size = DATA.length) : (this.size = size));

             }

             @Override

             public int size() {

                 return size;

             }

             @Override

             public Iterator<Map.Entry<String, String>> iterator() {

                 return new Iterator<Map.Entry<String, String>>() {

                     // Only one Entry object per Iterator:

                     private Entry entry = new Entry(-1);

                     @Override

                     public boolean hasNext() {

                         return entry.index < size - 1;

                     }

                     @Override

                     public java.util.Map.Entry<String, String> next() {

                         entry.index++;

                         return entry;

                     }

                 };

             }

         }

         // (2) 实现Map.Entry<K,V>接口

         // 定制自己的Map.Entry实现Map.Entry<K, V>接口， 需要实现下面的方法

         // 每个Map.Entry对象都只存了它们的索引，而不是实际的键值。当调用getKey()， getValue()时，才会用索引返回恰当的元素

         private static class Entry implements Map.Entry<String, String> {

             int index;

             Entry(int index) {

                 this.index = index;

             }

             @Override

             public boolean equals(Object o) {

                 return DATA[index][0].equals(o);

             }

             @Override

             public String getKey() {

                 return DATA[index][0];

             }

             @Override

             public String getValue() {

                 return DATA[index][1];

             }

             @Override

             public String setValue(String value) {

                 throw new UnsupportedOperationException();

             }

             @Override

             public int hashCode() {

                 return DATA[index][0].hashCode();

             }

         }

     }

     // 取Map全部内容

     public static Map<String, String> capitals() {

         return selectAll();

     }

     // 取Map全部内容的key

     public static List<String> names() {

         return new ArrayList<String>(capitals().keySet());

     }

     // 取Map部分内容

     public static Map<String, String> capitals(final int size) {

         return select(size);

     }

     // 取Map部分内容的key

     public static List<String> names(int size) {

         return new ArrayList<String>(select(size).keySet());

     }

     private static Map<String, String> selectAll() {

         return new FlyweightMap();

     }

     private static Map<String, String> select(final int size) {

         return new FlyweightMap(size);

     }

 }

 public class Test4 {

     public static void main(String[] args) {

         System.out.println(Countries.capitals(5)); // {SOUTH AFRICA=Cape Town, SUDAN=Khartoum, CHINA=Beijing, JAPAN=Tokyo, SOUTH KOREA=Seoul}

         System.out.println(Countries.names(5)); // [SOUTH AFRICA, SUDAN, CHINA, JAPAN, SOUTH KOREA]

         System.out.println(new HashMap<String, String>(Countries.capitals(3))); // {SUDAN=Khartoum, CHINA=Beijing, SOUTH AFRICA=Cape Town}

         System.out.println(new LinkedHashMap<String, String>(Countries.capitals(3))); // {SOUTH AFRICA=Cape Town, SUDAN=Khartoum, CHINA=Beijing}

         System.out.println(new TreeMap<String, String>(Countries.capitals(3))); // {CHINA=Beijing, SOUTH AFRICA=Pretoria/Cape Town, SUDAN=Khartoum}

         System.out.println(new Hashtable<String, String>(Countries.capitals(3))); // {SUDAN=Khartoum, SOUTH AFRICA=Pretoria/Cape Town, CHINA=Beijing}

         System.out.println(new HashSet<String>(Countries.names(4))); // [SUDAN, CHINA, SOUTH AFRICA, JAPAN]

         System.out.println(new LinkedHashSet<String>(Countries.names(4))); // [SOUTH AFRICA, SUDAN, CHINA, JAPAN]

         System.out.println(new TreeSet<String>(Countries.names(4))); // [CHINA, JAPAN, SOUTH AFRICA, SUDAN]

         System.out.println(new ArrayList<String>(Countries.names(4))); // [SOUTH AFRICA, SUDAN, CHINA, JAPAN]

         System.out.println(new LinkedList<String>(Countries.names(4))); // [SOUTH AFRICA, SUDAN, CHINA, JAPAN]

         System.out.println(Countries.capitals().get("BRAZIL")); // Brasilia

     }

 }