HashMap<A, String> map
//略过初始化，保证里面不会有空key和空value
map.forEach((key, value) ->
System.out.println("map contains key? : " + map.containsKey(key))
});
//略过初始化，保证里面不会有空key和空value
map.forEach((key, value) ->
System.out.println("map contains key? : " + map.containsKey(key))
});
