java.util.Collections.newSetFromMap() 方法

package com.codingdict;

import java.util.*;

public class CollectionsDemo {
   public static void main(String args[]) {

      // create map
      Map<String, Boolean> map = new WeakHashMap<String, Boolean>();

      // create a set from map
      Set<String> set = Collections.newSetFromMap(map);

      // add values in set
      set.add("Java");
      set.add("C");
      set.add("C++");

      // set and map values are
      System.out.println("Set is: " + set);
      System.out.println("Map is: " + map);
   }
}