逻辑：
set是无序不重复数据元素的集合。
map是另一种set，如果将<key,value>看成一个整体的话，其实就是set。在map中，若用map的keyset()方法将key提取出来，便构成了一个set集合。
所以，就定义一个整体SimpleEntry<K,V>作为元素存入set。
代码：
/*
*SimpleEntry<K,V>作为map对象的存储元素
*/
class SimpleEntry<K, V>
implements Map.Entry<K, V>, Serializable {// map中的key不可变
private final K key; private V value;public SimpleEntry(K paramK, V paramV)
{ this.key = paramK; this.value = paramV; }
public SimpleEntry(Map.Entry<? extends K, ? extends V> paramEntry)
{ this.key = paramEntry.getKey(); this.value = paramEntry.getValue(); }public K getKey()
{ return this.key; }public V getValue()
{ return this.value; }public V setValue(V paramV)
{ Object localObject = this.value; this.value = paramV; return localObject; }public boolean equals(Object paramObject)
{ if (paramObject == this) { return true; } if (paramObject.getClass() == SimpleEntry.class) { SimpleEntry localSimpleEntry = (SimpleEntry)paramObject; return localSimpleEntry.getKey().equals(getKey()); } return false; }public int hashCode()
{ return this.key == null ? 0 : this.key.hashCode(); }public String toString()
{ return this.key + "=" + this.value; } }
/*
*Set2Map<K, V>继承自hashset，底层是利用hashset来存储，但存储的是<K，V>这样的二元组，所以可以看成是一个map
*/
public class Set2Map<K, V> extends HashSet<SimpleEntry<K, V>>
{ public void clear() { super.clear(); }public boolean containsKey(K paramK)
{ return super.contains(new SimpleEntry(paramK, null)); }boolean containsValue(Object paramObject)
{ for (SimpleEntry localSimpleEntry : this) { if (localSimpleEntry.getValue().equals(paramObject)) { return true; } } return false; }public V get(Object paramObject)
{ for (SimpleEntry localSimpleEntry : this) { if (localSimpleEntry.getKey().equals(paramObject)) { return localSimpleEntry.getValue(); } } return null; }public V put(K paramK, V paramV)
{ add(new SimpleEntry(paramK, paramV)); return paramV; }
//内部用了迭代器实现
public void putAll(Map<? extends K, ? extends V> paramMap)
{ for (Iterator localIterator = paramMap.keySet().iterator(); localIterator.hasNext(); ) { Object localObject = localIterator.next();add(new SimpleEntry(localObject, paramMap.get(localObject)));
} }//内部用了迭代器实现
public V removeEntry(Object paramObject)
{ Iterator localIterator = iterator(); while (localIterator.hasNext()) { SimpleEntry localSimpleEntry = (SimpleEntry)localIterator.next(); if (localSimpleEntry.getKey().equals(paramObject)) { Object localObject = localSimpleEntry.getValue(); localIterator.remove(); return localObject; } } return null; }public int size()
{ return super.size(); } }
测试程序：
public class Set2MapTest
{ public static void main(String[] paramArrayOfString) { Set2Map localSet2Map = new Set2Map();localSet2Map.put("语文", Integer.valueOf(89));
localSet2Map.put("数学", Integer.valueOf(83)); localSet2Map.put("英文", Integer.valueOf(80)); System.out.println(localSet2Map);System.out.println(localSet2Map.size());
localSet2Map.removeEntry("数学"); System.out.println("删除key为\"数学\"的Entry之后：" + localSet2Map);System.out.println("语文成绩：" + localSet2Map.get("语文"));
System.out.println("是否包含\"英文\"key :" + localSet2Map.containsKey("英文"));
System.out.println("是否包含 82 value :" + localSet2Map.containsValue(Integer.valueOf(82)));
localSet2Map.clear();
System.out.println("执行clear()方法之后的集合：" + localSet2Map); } }
reference：
1. 《疯狂java，突破程序员基本功的16课》 李刚。