享元Map

这里之所以叫享元，注意static关键字。 定制了Entry 和 EntrySet

 

public class Countries {
	
	public static final String[][] DATA = {
		{"CHINA","BEIJING"}
	};
	
	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 String getKey() {
				return DATA[index][0];
			}
			public String getValue() {
				return DATA[index][1];
			}
			public String setValue(String value) {
				throw new UnsupportedOperationException();
			}
			public boolean equals(Object o){
				return DATA[index][0].equals(o);
			}
			public int hashCode(){
				return DATA[index][0].hashCode();
			}
		}
		
		static class EntrySet extends AbstractSet<Map.Entry<String, String>>{
			private int size;
			EntrySet(int size){
				if(size<0)
					this.size = 0;
				else if(size>DATA.length)
					this.size = DATA.length;
				else
					this.size = size;
			}
			public Iterator<java.util.Map.Entry<String, String>> iterator() {
				return new Iter();
			}

			@Override
			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);
				@Override
				public boolean hasNext() {
					return entry.index < size-1;
				}

				@Override
				public java.util.Map.Entry<String, String> next() {
					entry.index++;
					return entry;
				}

				@Override
				public void remove() {
					throw new UnsupportedOperationException();
				}
			}
		}
	
		
		public Set<java.util.Map.Entry<String, String>> entrySet() {
			return entries;
		}
		
		private static Set<Map.Entry<String, String>> entries =
			new EntrySet(DATA.length);
		
	}
	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;
	}
	
	public static Map<String, String> capitals(int size){
		return select(size);
	}
	
	static List<String> names = new ArrayList<String>(map.keySet());
	
	public static List<String> names(){
		return names;
	}
	
	public static List<String> names(int size){
		return new ArrayList<String>(select(size).keySet());
	}
	
	public static void main(String[] args) {
		System.out.println(new TreeMap<String, String>(capitals(3)));
	}
	
}