package com.jackie;import java.util.*;/** * Created by zhimeng on 15/11/18. */public class Countries { public static String[][] DATA = new String[][]{ {"China", "Beijing"}, {"Japan", "Tokyo"}, {"Taiwan", "Taibei"}, {"Zhejian", "Hangzhou"}, {"Hubei", "Wuhan"}, {"Jiangsu", "Nanjing"} }; public static void main(String[] args) { System.out.println(Countries.DATA); }}class FlyweightMap extends AbstractMap<String, String> { public static void main(String[] args) { System.out.println(Countries.DATA); } @Override public Set<Map.Entry<String, String>> entrySet() { return entries; } private static class Entry implements Map.Entry<String, String> { int index = -1; public Entry(int index) { this.index = index; } public String getKey() { return Countries.DATA[index][0]; } public String getValue() { return Countries.DATA[index][1]; } public String setValue(String value) { throw new UnsupportedOperationException(); } @Override public boolean equals(Object obj) { return Countries.DATA[index][0].equals(obj); } @Override public int hashCode() { return Countries.DATA[index][0].hashCode(); } } private static class EntrySet extends AbstractSet<Map.Entry<String, String>> { private int size; private Entry entry = new Entry(-1); public EntrySet(int size) { if (size < 0) { this.size = 0; } else if (size > Countries.DATA.length) { this.size = Countries.DATA.length; } else { this.size = size; } } @Override public Iterator<Map.Entry<String, String>> iterator() { return new Iter(); } @Override public int size() { return size; } private class Iter implements Iterator<Map.Entry<String, String>> { public boolean hasNext() { System.out.println("size: " + size); ／／这里除了错误。因为这个判断条件应该是size-1; return entry.index < size-1; } public Map.Entry<String, String> next() { entry.index++; System.out.println("entry index: " + entry.index); return entry; } } } private static Set<Map.Entry<String, String>> entries = new EntrySet(Countries.DATA.length); public static Map<String, String> select(final int size) { return new FlyweightMap() { @Override public Set<Map.Entry<String, String>> entrySet() { return new EntrySet(size); } }; } public 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()); }}
ps： 因为map 在生成keySet（） 的时候，会调用entrySet（）。 仅供自己bug的记录。
相关资源：敏捷开发V1.0.pptx
