public static void testCM(){
Map<Integer , String> hs = new HashMap<Integer , String>();
int i = 0;
hs.put(199, "序号:"+201);
while(i<50){
hs.put(i, "序号:"+i);
i++;
}
hs.put(-1, "序号:"+200);
hs.put(200, "序号:"+200);
for(Entry<Integer , String> entry : hs.entrySet()){
System.out.println("key:"+entry.getKey()+" value:"+entry.getValue());
}
Iterator<Map.Entry<Integer , String>> iterator = hs.entrySet().iterator();
while(iterator.hasNext()){
Entry<Integer , String> entry = iterator.next();
System.out.println("key:"+entry.getKey()+" value:"+entry.getValue());
};
for(Integer key : hs.keySet()){
System.out.println("key:"+key+" value:"+hs.get(key));
};
Iterator keyIterator = hs.keySet().iterator();
while(keyIterator.hasNext()){
Integer key = (Integer)keyIterator.next();
System.out.println("key:"+key+" value:"+hs.get(key));
}
}
(1)使用keyset的两种方式都会遍历两次,所以效率没有使用EntrySet高。
(2)HashMap输出是无序的,这个无序不是说每次遍历的结果顺序不一样,而是说与插入顺序不一样。