Map的遍历

HashMap      异步操作，线程不安全  key value 可以保存为null

HashTable     同步操作，线程安全，  key value 不可以保存为null

Map<String,Integer> map1 = new HashMap<String,Integer>();

map1.put("一", 1);
map1.put("二", 2);
map1.put("三", 3);
//方法一
Set<Entry<String,Integer>> set = map1.entrySet();
Iterator<Entry<String,Integer>> it = set.iterator();
while(it.hasNext()) {
Entry<String, Integer> mapentry = it.next();
System.out.println(mapentry.getKey()+"="+mapentry.getValue());
}
//方法二
Set<String> twoset = map1.keySet();
Iterator<String> twoit = twoset.iterator();
while(twoit.hasNext()) {
String str = twoit.next();
System.out.println(str + "=" + map1.get(str));
}