HashMap hp = new HashMap();
      hp.put("1", "2");
      System.out.println(hp.keySet());

------解决方案--------------------
HashMap m = new HashMap();
Set keys = m.keySet(); // 获取主键集合


------解决方案--------------------
Java code
import java.util.*;
class MapTest{
    public static void main(String[] args){
        HashMap hm=new HashMap();
        hm.put("one","aaa");
        hm.put("two","bbb");
        hm.put("three","ccc");
        hm.put("four","ddd");
        hm.remove("three");
        hm.put("five","eee");
        Set set=hm.entrySet();
        Iterator it=set.iterator();
        while(it.hasNext()){
            Map.Entry me=(Map.Entry)it.next();
            System.out.println(me.getKey()+":"+me.getValue()+":"+me.hashCode());
        }
        
    }
}

------解决方案--------------------
o

------解决方案--------------------
用 keySet() 方法

------解决方案--------------------
 HashMap hsMap = new HashMap();
   hsMap.put("one","aaa");
   hsMap.put("two","bbb");

   Enumeration eCol = htCol.keys();

   while( eCol.hasMoreElements()){
       System.out.println(eCol.nextElement());
   }

给不给加分!!!!

------解决方案--------------------
import java.util.*;
class MapTest{
   public static void main(String[] args){
       HashMap hm=new HashMap();
       hm.put("one","aaa");
       hm.put("two","bbb");
       hm.put("three","ccc");
       hm.put("four","ddd");
       hm.put("five","eee");
       Set set=hm.entrySet();
       Iterator it=set.iterator();
       while(it.hasNext()){
           Map.Entry me=(Map.Entry)it.next();
           System.out.println(me.getKey());        }
      
   }
}