Hashmap遍历选择Keyset还是entryset?

public class HashMapTest {
 
public static void main(String[] args) {
HashMap hashmap = new HashMap();
for(int i=0;i<1000;i++){
hashmap.put(""+i,"hello");
}
 
long bs = Calendar.getInstance().getTimeInMillis();
Iterator iterator = hashmap.keySet().iterator();
while(iterator.hasNext()) {
System.out.println(hashmap.get(iterator.next()));
}
System.out.println(Calendar.getInstance().getTimeInMillis() - bs);
listHashMap();
}
 
public static void listHashMap(){
java.util.HashMap hashmap = new java.util.HashMap();
for(int i=0;i<1000;i++){
hashmap.put(""+i,"hello");
}
long bs = Calendar.getInstance().getTimeInMillis();
//Set set = hashmap.entrySet() ;
java.util.Iterator it = hashmap.entrySet().iterator();
while(it.hasNext()){
java.util.Map.Entry entry = (java.util.Map.Entry)it.next();
// entry.getKey() 返回与此项对应的键
// entry.getValue() 返回与此项对应的值
System.out.println(entry.getValue());
}
System.out.println(Calendar.getInstance().getTimeInMillis() - bs);
}
 
}