first day
1, the use of "key-value pair to" walk the wrong way Map collection argument is ()
A, .map collection can not be used directly or enhanced for an iterator to traverse to get all the keys Map collection of objects is its traversal of a
B, Map set after obtaining the key value of the object, call the get () method wherein data can be acquired.
C, Map get all keys set to the object via the entrySet () method.
D, generics Map and its key collection of consistent generic object.