Java 集合 HashSet和HashMap的区别

Set s = Collections.synchronizedSet(new HashSet(...));

 Map m = Collections.synchronizedMap(new HashMap(...));

import java.util.HashSet;
class HashSetDemo{ 
  public static void main(String[] args) {
     // Create a HashSet
     HashSet<String> hset = new HashSet<String>();

     //add elements to HashSet
     hset.add("AA");
     hset.add("BB");
     hset.add("CC");
     hset.add("DD");

     // Displaying HashSet elements
     System.out.println("HashSet contains: ");
     for(String temp : hset){
        System.out.println(temp);
     }
  }
}

HashSet contains: 
AA
BB
CC
DD

import java.util.HashMap;
class HashMapDemo{ 
  public static void main(String[] args) {
     // Create a HashMap
     HashMap<Integer, String> hmap = new HashMap<Integer, String>();

     //add elements to HashMap
     hmap.put(1, "AA");
     hmap.put(2, "BB");
     hmap.put(3, "CC");
     hmap.put(4, "DD");

     // Displaying HashMap elements
     System.out.println("HashMap contains: "+hmap);
  }
}

HashMap contains: {1=AA, 2=BB, 3=CC, 4=DD}