java遍历hashMap、hashSet、Hashtable

原文

一.遍历HashMapMap<Integer, String> map = new HashMap<Integer, String>();  for(int i=0;i<100;i++)  {   map.put(i, "123");  }方法一：效率比方法二高for(Entry<Integer, String> entry:map.entrySet())  {   System.out.println(entry.getKey()+"="+entry.getValue());  }方法二：for(Object obj : map.keySet()) {           Object key = obj;           Object value = map.get(obj);           System.out.println(value);  }二.遍历HashSetSet set = new HashSet();  for(int i=0;i<100;i++)  {   set .add("123");  }for(Iterator it=set.iterator();it.hasNext();)  {   System.out.println(it.next());  }三.遍历Hashtable(同步、线程安全的)Hashtable table = new Hashtable();  table.put(1, "1");  table.put(2, "1");  table.put(3, "1");  //遍历key  Enumeration e = table.keys();  while( e. hasMoreElements() ){  System.out.println( e.nextElement() );  }  //遍历value  e = table.elements();  while( e. hasMoreElements() ){  System.out.println( e.nextElement() );  }