HashMap, HashSet, HashMap Iterator

一.遍历HashMap

Map<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HashSet

Set 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() );

}