public class Test
{
public static void main(String[] args)
{
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
Integer i1 = null;
Integer i2 = null;
map.put(i1, i2);
Iterator<Integer> it = map.keySet().iterator();
while(it.hasNext()){
System.out.println(map.get(it.next()));
}
}
}
输出结果为:null